The influence of n-butanol blending on the ignition delay times of gasoline and its surrogate at high pressures

KAUST Repository

Agbro, Edirin

2016-09-24

The influence of blending n-butanol at 20% by volume on the ignition delay times for a reference gasoline was studied in a rapid compression machine (RCM) for stoichiometric fuel/air mixtures at 20 bar and 678-858 K. Delay times for the blend lay between those of stoichiometric gasoline and stoichiometric n-butanol across the temperature range studied. At lower temperatures, delays for the blend were however, much closer to those of n-butanol than gasoline despite n-butanol being only 20% of the mixture. Under these conditions n-butanol acted as an octane enhancer over and above what might be expected from a simple linear blending law. The ability of a gasoline surrogate, based on a toluene reference fuel (TRF), to capture the main trends of the gasoline/n-butanol blending behaviour was also tested within the RCM. The 3-component TRF based on a mixture of toluene, n-heptane and iso-octane was able to capture the trends well across the temperature range studied. Simulations of ignition delay times were also performed using a detailed blended n-butanol/TRF mechanism based on the adiabatic core assumption and volume histories from the experimental data. Overall, the model captured the main features of the blending behaviour, although at the lowest temperatures, predicted ignition delays for stoichiometric n-butanol were longer than those observed. A brute-force local sensitivity analysis was performed to evaluate the main chemical processes driving the ignition behaviour of the TRF, n-butanol and blended fuels. The reactions of fuel + OH dominated the sensitivities at lower temperatures, with H abstraction from n-butanol from a and 7 sites being key for both the n-butanol and the blend. At higher temperatures the decomposition of H2O2 and reactions of HO2 and that of formaldehyde with OH became critical, in common with the ignition behaviour of other fiiels. Remaining uncertainties in the rates of these key reactions are discussed. Crown Copyright (C) 2016 Published

Ignition delay measurements of light naphtha: A fully blended low octane fuel

KAUST Repository

Javed, Tamour

2016-06-15

Light naphtha is a fully blended, low-octane (RON. = 64.5, MON. = 63.5), highly paraffinic (>. 90% paraffinic content) fuel, and is one of the first distillates obtained during the crude oil refining process. Light naphtha is an attractive low-cost fuel candidate for advanced low-temperature compression ignition engines where autoignition is the primary control mechanism. We measured ignition delay times for light naphtha in a shock tube and a rapid compression machine (RCM) over a broad range of temperatures (640-1250. K), pressures (20 and 40. bar) and equivalence ratios (0.5, 1 and 2). Ignition delay times were modeled using a two-component primary reference fuel (PRF) surrogate and a multi-component surrogate. Both surrogates adequately captured the measured ignition delay times of light naphtha under shock tube conditions. However, for low-temperature RCM conditions, simulations with the multi-component surrogate showed better agreement with experimental data. These simulated surrogate trends were confirmed by measuring the ignition delay times of the PRF and multi-component surrogates in the RCM at . P = 20. bar, . ϕ = 2. Detailed kinetic analyses were undertaken to ascertain the dependence of the surrogates\\' reactivity on their chemical composition. To the best of our knowledge, this is the first fundamental autoignition study on the reactivity of a low-octane fully blended fuel and the use of a suitably formulated multi-component surrogate to model its behavior.

Delaying sawtooth oscillations in the Compact Ignition Tokamak

International Nuclear Information System (INIS)

Bateman, G.

1986-09-01

A combination of pellets, off-axis heating, and current ramp is used to delay the onset of sawtooth oscillations for 3.4 seconds and achieve ignition with less than 0.2-second confinement time in a 1-1/2-D BALDUR simulation of the Compact Ignition Tokamak. Deuterium and tritium pellets are injected into an initially cold, relatively low density plasma, where they cool the center and produce a very centrally peaked density profile. A centrally peaked density profile (n/sub e0// = 4.0) is subsequently maintained by an inward particle pinch. Twenty megawatts of auxiliary heating is applied halfway between the magnetic axis and the edge of the plasma for 2 seconds after the pellets are injected. The plasma ignites and then burns from the time the auxiliary heating is turned off until the first large sawtooth crash occurs at 3.4 seconds. The burn would be expected to continue after that only if the sawtooth period is sufficiently long (roughly 0.3 seconds or longer)

Effect of laser induced plasma ignition timing and location on Diesel spray combustion

International Nuclear Information System (INIS)

Pastor, José V.; García-Oliver, José M.; García, Antonio; Pinotti, Mattia

2017-01-01

Highlights: • Laser plasma ignition is applied to a direct injection Diesel spray, compared with auto-ignition. • Critical local fuel/air ratio for LIP provoked ignition is obtained. • The LIP system is able to stabilize Diesel combustion compared to auto-ignition cases. • Varying LIP position along spray axis directly affects Ignition-delay. • Premixed combustion is reduced both by varying position and delay of the LIP ignition system. - Abstract: An experimental study about the influence of the local conditions at the ignition location on combustion development of a direct injection spray is carried out in an optical engine. A laser induced plasma ignition system has been used to force the spray ignition, allowing comparison of combustion’s evolution and stability with the case of conventional autoignition on the Diesel fuel in terms of ignition delay, rate of heat release, spray penetration and soot location evolution. The local equivalence ratio variation along the spray axis during the injection process was determined with a 1D spray model, previously calibrated and validated. Upper equivalence ratios limits for the ignition event of a direct injected Diesel spray, both in terms of ignition success possibilities and stability of the phenomena, could been determined thanks to application of the laser plasma ignition system. In all laser plasma induced ignition cases, heat release was found to be higher than for the autoignition reference cases, and it was found to be linked to a decrease of ignition delay, with the premixed peak in the rate of heat release curve progressively disappearing as the ignition delay time gets shorter. Ignition delay has been analyzed as a function of the laser position, too. It was found that ignition delay increases for plasma positions closer to the nozzle, indicating that the amount of energy introduced by the laser induced plasma is not the only parameter affecting combustion initiation, but local equivalence ratio

Investigation into the effect of different fuels on ignition delay of M-type diesel combustion process

Directory of Open Access Journals (Sweden)

Bibić Dževad

2008-01-01

Full Text Available An ignition delay is a very complex process which depends on a great number of parameters. In practice, definition of the ignition delay is based on the use of correlation expressions. However, the correlation expressions have very often limited application field. This paper presents a new correlation which has been developed during the research project on the direct injection M-type diesel engine using both the diesel and biodiesel fuel, as well as different values of a static injection timing. A dynamic start of injection, as well as the ignition delay, is defined in two ways. The first approach is based on measurement of a needle lift, while the second is based on measurement of a fuel pressure before the injector. The latter approach requires calculation of pressure signals delay through the fuel injection system and the variation of a static advance injection angle changing. The start of a combustion and the end of the ignition delay is defined on the basis of measurements of an in-cylinder pressure and its point of separation from a skip-fire pressure trace. The developed correlation gives better prediction of the ignition delay definition for the M-type direct injection diesel engine in the case of diesel and biodiesel fuel use when compared with the classic expression by the other authors available in the literature.

Knock Prediction Using a Simple Model for Ignition Delay

KAUST Repository

Kalghatgi, Gautam

2016-04-05

An earlier paper has shown the ability to predict the phasing of knock onset in a gasoline PFI engine using a simple ignition delay equation for an appropriate surrogate fuel made up of toluene and PRF (TPRF). The applicability of this approach is confirmed in this paper in a different engine using five different fuels of differing RON, sensitivity, and composition - including ethanol blends. An Arrhenius type equation with a pressure correction for ignition delay can be found from interpolation of previously published data for any gasoline if its RON and sensitivity are known. Then, if the pressure and temperature in the unburned gas can be estimated or measured, the Livengood-Wu integral can be estimated as a function of crank angle to predict the occurrence of knock. Experiments in a single cylinder DISI engine over a wide operating range confirm that this simple approach can predict knock very accurately. The data presented should enable engineers to study knock or other auto-ignition phenomena e.g. in premixed compression ignition (PCI) engines without explicit chemical kinetic calculations. © Copyright 2016 SAE International.

Estimating fuel octane numbers from homogeneous gas-phase ignition delay times

KAUST Repository

Naser, Nimal

2017-11-05

Fuel octane numbers are directly related to the autoignition properties of fuel/air mixtures in spark ignition (SI) engines. This work presents a methodology to estimate the research and the motor octane numbers (RON and MON) from homogeneous gas-phase ignition delay time (IDT) data calculated at various pressures and temperatures. The hypothesis under investigation is that at specific conditions of pressure and temperature (i.e., RON-like and MON-like conditions), fuels with IDT identical to that of a primary reference fuel (PRF) have the same octane rating. To test this hypothesis, IDTs with a detailed gasoline surrogate chemical kinetic model have been calculated at various temperatures and pressures. From this dataset, temperatures that best represent RON and MON have been correlated at a specified pressure. Correlations for pressures in the range of 10–50 bar were obtained. The proposed correlations were validated with toluene reference fuels (TRF), toluene primary reference fuels (TPRF), ethanol reference fuels (ERF), PRFs and TPRFs with ethanol, and multi-component gasoline surrogate mixtures. The predicted RON and MON showed satisfactory accuracy against measurements obtained by the standard ASTM methods and blending rules, demonstrating that the present methodology can be a viable tool for a first approximation. The correlations were also validated against an extensive set of experimental IDT data obtained from literature with a high degree of accuracy in RON/MON prediction. Conditions in homogeneous reactors such as shock tubes and rapid compression machines that are relevant to modern SI engines were also identified. Uncertainty analysis of the proposed correlations with linear error propagation theory is also presented.

Estimating fuel octane numbers from homogeneous gas-phase ignition delay times

KAUST Repository

Naser, Nimal; Sarathy, Mani; Chung, Suk-Ho

2017-01-01

Fuel octane numbers are directly related to the autoignition properties of fuel/air mixtures in spark ignition (SI) engines. This work presents a methodology to estimate the research and the motor octane numbers (RON and MON) from homogeneous gas-phase ignition delay time (IDT) data calculated at various pressures and temperatures. The hypothesis under investigation is that at specific conditions of pressure and temperature (i.e., RON-like and MON-like conditions), fuels with IDT identical to that of a primary reference fuel (PRF) have the same octane rating. To test this hypothesis, IDTs with a detailed gasoline surrogate chemical kinetic model have been calculated at various temperatures and pressures. From this dataset, temperatures that best represent RON and MON have been correlated at a specified pressure. Correlations for pressures in the range of 10–50 bar were obtained. The proposed correlations were validated with toluene reference fuels (TRF), toluene primary reference fuels (TPRF), ethanol reference fuels (ERF), PRFs and TPRFs with ethanol, and multi-component gasoline surrogate mixtures. The predicted RON and MON showed satisfactory accuracy against measurements obtained by the standard ASTM methods and blending rules, demonstrating that the present methodology can be a viable tool for a first approximation. The correlations were also validated against an extensive set of experimental IDT data obtained from literature with a high degree of accuracy in RON/MON prediction. Conditions in homogeneous reactors such as shock tubes and rapid compression machines that are relevant to modern SI engines were also identified. Uncertainty analysis of the proposed correlations with linear error propagation theory is also presented.

Experimental and numerical assessment of ignition delay period for pure diesel and biodiesel B20

Science.gov (United States)

Aldhaidhawi, Mohanad; Brabec, Marek; Lucian, Miron; Chiriac, Radu; Bădescu, Viorel

2017-10-01

The ignition delay period for a compression ignition engine fueled alternatively with pure diesel and with biodiesel B20 has been experimentally and numerically investigated. The engine was operated under full load conditions for two speeds, 1400 rpm speed for maximum brake torque and 2400 rpm speed for maximum brake power. Different parameters suggested as important to define the start of combustion have been considered before the acceptance of a certain evaluation technique of ignition delay. Correlations between these parameters were analyzed and concluded about the best method to identify the start of combustion. The experimental results were further compared with the ignition delay predicted by some correlations. The results showed that the determined ignition delays are in good agreement with those of the Arrhenius type expressions for pure diesel fuel, while for biodiesel B20 the correlation results are significantly different than the experimental results.

A shock tube and laser absorption study of ignition delay times and OH reaction rates of ketones: 2-Butanone and 3-buten-2-one

KAUST Repository

Badra, Jihad; Elwardani, Ahmed Elsaid; Khaled, Fathi; Vasu, Subith S.; Farooq, Aamir

2014-01-01

Ketones are potential biofuel candidates and are also formed as intermediate products during the oxidation of large hydrocarbons or oxygenated fuels, such as alcohols and esters. This paper presents shock tube ignition delay times and OH reaction

Prediction of biodiesel ignition delay in a diesel engine using artificial neural networks

International Nuclear Information System (INIS)

Piloto-Rodríguez, Ramón; Sánchez-Borroto, Yisel

2017-01-01

Ignition delay is one of the most important parameters of the combustion process and have a strong influence in exhaust emissions and engines performance. In the present work, the results of the mathematical modeling of ignition delay through artificial neural networks are shown. The modeling starts from input values that cover thermodynamic variables, engines parameters and biodiesel properties. The model obtained is only useful for biodiesel samples and several neural network algorithms were applied in order to predict the ignition delay. From its correlation coefficient, prediction capability and lowest absolute error, the best model was selected. Among other network’s input parameters, the cetane number was taken into account, also previously predicted by the use of ANN. (author)

Diesel ignition delay and lift-off length through different methodologies using a multi-hole injector

International Nuclear Information System (INIS)

Payri, Raúl; Salvador, F.J.; Manin, Julien; Viera, Alberto

2016-01-01

Highlights: • Lift-off length and ignition delay are measured through different methodologies. • Oxygen concentration, temperature and injection pressure sweeps are performed. • A multi hole injector is compared with an equivalent single hole injector. • Multi hole injector has shorter ignition delay and lift-off length than single hole. • Empirical correlations were calculated for an analytical description of the results. - Abstract: In this paper, lift-off length has been measured via both broadband luminosity and OH chemiluminescence. In addition, ignition delay has also been measured via broadband chemiluminescence and Schlieren imaging. A 3 orifice injector from the Engine Combustion Network (ECN) set, referred to as Spray B, and a single component fuel (n-dodecane) was used. Experiments were carried out in a constant flow and pressure facility, that allowed to reproduce engine-like thermodynamic conditions, and enabled the study to be performed over a wide range of test conditions with a very high repetition rate. Data obtained was also compared with results from a single orifice injector also from the Engine Combustion Network, with analog orifice characteristics (90 μm outlet diameter and convergent shape) and technology as the injector used. Results showed that there is good correlation between the ignition delay measured through both methodologies, that oxygen concentration and injection pressure plays a minor role in the ignition delay, being ambient temperature and density the parameters with the highest influence. Lift-off length measurements showed significant differences between methodologies. Minor deviation was observed between injectors with different nozzle geometry (seat inclination angle), due to temperature variations along the chamber, highlighting the importance of temperature distribution along combustion vessels. Empirical correlations for lift-off and ignition delay were calculated, underlining the effect of the conditions on

Knock Prediction Using a Simple Model for Ignition Delay

KAUST Repository

Kalghatgi, Gautam; Morganti, Kai; Algunaibet, Ibrahim; Sarathy, Mani; Dibble, Robert W.

2016-01-01

An earlier paper has shown the ability to predict the phasing of knock onset in a gasoline PFI engine using a simple ignition delay equation for an appropriate surrogate fuel made up of toluene and PRF (TPRF). The applicability of this approach

Ignition delay times of Gasoline Distillation Cuts measured with Ignition Quality Tester

KAUST Repository

Naser, Nimal; Singh, Eshan; Ahmed, Ahfaz; Sarathy, Mani

2017-01-01

Tailoring fuel properties to maximize the efficiency of internal combustion engines is a way towards achieving cleaner combustion systems. In this work, the ignition properties of various gasoline fuel distillation cuts are analyzed to better

Ignition delay and soot oxidative reactivity of MTBE blended diesel fuel

KAUST Repository

Yang, Seung Yeon; Naser, Nimal; Chung, Suk-Ho; Al-Qurashi, Khalid

2014-01-01

Methyl tert-butyl ether (MTBE) was added to diesel fuel to investigate the effect on ignition delay and soot oxidative reactivity. An ignition quality tester (IQT) was used to study the ignition propensity of MTBE blended diesel fuels in a reactive spray environment. The IQT data showed that ignition delay increases linearly as the MTBE fraction increases in the fuel. A four-stroke single cylinder diesel engine was used to generate soot samples for a soot oxidation study. Soot samples were pre-treated using a tube furnace in a nitrogen environment to remove any soluble organic fractions and moisture content. Non-isothermal oxidation of soot samples was conducted using a thermogravimetric analyzer (TGA). It was observed that oxidation of 'MTBE soot' started began at a lower temperature and had higher reaction rate than 'diesel soot' across a range of temperatures. Several kinetic analyses including an isoconversional method and a combined model fitting method were carried out to evaluate kinetic parameters. The results showed that Diesel and MTBE soot samples had similar activation energy but the pre-exponential factor of MTBE soot was much higher than that of the Diesel soot. This may explain why MTBE soot was more reactive than Diesel soot. It is suggested that adding MTBE to diesel fuel is better for DPF regeneration since an MTBE blend can significantly influence the ignition characteristics and, consequently, the oxidative reactivity of soot. Copyright © 2014 SAE International.

Ignition delay and soot oxidative reactivity of MTBE blended diesel fuel

KAUST Repository

Yang, Seung Yeon

2014-04-01

Methyl tert-butyl ether (MTBE) was added to diesel fuel to investigate the effect on ignition delay and soot oxidative reactivity. An ignition quality tester (IQT) was used to study the ignition propensity of MTBE blended diesel fuels in a reactive spray environment. The IQT data showed that ignition delay increases linearly as the MTBE fraction increases in the fuel. A four-stroke single cylinder diesel engine was used to generate soot samples for a soot oxidation study. Soot samples were pre-treated using a tube furnace in a nitrogen environment to remove any soluble organic fractions and moisture content. Non-isothermal oxidation of soot samples was conducted using a thermogravimetric analyzer (TGA). It was observed that oxidation of \\'MTBE soot\\' started began at a lower temperature and had higher reaction rate than \\'diesel soot\\' across a range of temperatures. Several kinetic analyses including an isoconversional method and a combined model fitting method were carried out to evaluate kinetic parameters. The results showed that Diesel and MTBE soot samples had similar activation energy but the pre-exponential factor of MTBE soot was much higher than that of the Diesel soot. This may explain why MTBE soot was more reactive than Diesel soot. It is suggested that adding MTBE to diesel fuel is better for DPF regeneration since an MTBE blend can significantly influence the ignition characteristics and, consequently, the oxidative reactivity of soot. Copyright © 2014 SAE International.

Kinetic mechanism of plasma-assisted ignition of hydrocarbons

International Nuclear Information System (INIS)

Kosarev, I N; Aleksandrov, N L; Kindysheva, S V; Starikovskaia, S M; Starikovskii, A Yu

2008-01-01

Ignition of hydrocarbon-containing gaseous mixtures has been studied experimentally and numerically under the action of a high-voltage nanosecond discharge at elevated temperatures. Ignition delay times were measured behind a reflected shock wave in stoichiometric C n H 2n+2 : O 2 mixtures (10%) diluted with Ar (90%) for n = 1-5. It was shown that the application of the gas discharge leads to more than an order of magnitude decrease in ignition delay time for all hydrocarbons under consideration. The measured values of ignition delay time agree well with the results of a numerical simulation of the ignition based on the calculation of atom and radical production during the discharge and in its afterglow. The analysis of simulation results showed that a non-equilibrium plasma favours the ignition mainly due to O atoms produced in the active phase of the discharge. (fast track communication)

The use of CO 2 as an additive for ignition delay and pollutant control in CH 4 /air autoignition

KAUST Repository

Tingas, Efstathios Al.

2017-10-05

The effect of CO2 dilution on the adiabatic and isochoric autoignition of CH4/air mixtures is analyzed with Computational Singular Perturbation (CSP) algorithmic tools, with a particular emphasis on the determination of the features of the chemical dynamics that control ignition delay and emission formation. Increasing CO2 dilution causes longer ignition delays, lower final temperatures and decreased formation of NO and CO. These effects of CO2 dilution are shown to be entirely thermal, contrary to what happens with dilution with H2O, which also has chemical activity and can reduce ignition delay. For the same initial mole fraction of the diluent, the decrease in final temperature and in NO concentration is larger in the CO2 case whereas the decrease in CO is larger in the H2O case. The thermal effect of CO2 is entirely analogous with those of dilution with the chemically inert Ar, only stronger for the same percentage of initial dilution, because of the larger specific heat of CO2. The reactions that have the largest contribution to the characteristic explosive time scale of the system during ignition delay (H2O2(+M)→OH+OH(+M), CH3O2+CH2O→CH3O2H+HCO, CH4+CH3O2→CH3+CH3O2H, H+O2→O+OH, etc.) are not substantially affected by CO2 dilution, neither are the species that are pointed by CSP (CH3O2, H2O2, CH2O, etc.) as having the largest impact on the this timescale. The same holds for the modes that control CO and NO formation. The results point to the possibility of cold exhaust gas recirculation being used in order to produce mixtures with longer ignition delays and therefore substantial resistance to uncontrolled ignition.

Auto-Ignition and Spray Characteristics of n-Heptane and iso-Octane Fuels in Ignition Quality Tester

KAUST Repository

Jaasim, Mohammed

2018-04-04

Numerical simulations were conducted to systematically assess the effects of different spray models on the ignition delay predictions and compared with experimental measurements obtained at the KAUST ignition quality tester (IQT) facility. The influence of physical properties and chemical kinetics over the ignition delay time is also investigated. The IQT experiments provided the pressure traces as the main observables, which are not sufficient to obtain a detailed understanding of physical (breakup, evaporation) and chemical (reactivity) processes associated with auto-ignition. A three-dimensional computational fluid dynamics (CFD) code, CONVERGE™, was used to capture the detailed fluid/spray dynamics and chemical characteristics within the IQT configuration. The Reynolds-averaged Navier-Stokes (RANS) turbulence with multi-zone chemistry sub-models was adopted with a reduced chemical kinetic mechanism for n-heptane and iso-octane. The emphasis was on the assessment of two common spray breakup models, namely the Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) and linearized instability sheet atomization (LISA) models, in terms of their influence on auto-ignition predictions. Two spray models resulted in different local mixing, and their influence in the prediction of auto-ignition was investigated. The relative importance of physical ignition delay, characterized by spray evaporation and mixing processes, in the overall ignition behavior for the two different fuels were examined. The results provided an improved understanding of the essential contribution of physical and chemical processes that are critical in describing the IQT auto-ignition event at different pressure and temperature conditions, and allowed a systematic way to distinguish between the physical and chemical ignition delay times.

An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements

KAUST Repository

Burke, Siné ad M.; Burke, Ultan; Mc Donagh, Reuben; Mathieu, Olivier; Osorio, Irmis; Keesee, Charles L.; Morones, Aní bal; Petersen, Eric L.; Wang, Weijing; DeVerter, Trent A.; Oehlschlaeger, Matthew A.; Rhodes, Brandie; Hanson, Ronald K.; Davidson, David F.; Weber, Bryan W.; Sung, Chihjen; Santner, Jeffrey S.; Ju, Yiguang; Haas, Francis M.; Dryer, Frederick L.; Volkov, Evgeniy N.; Nilsson, Elna J K; Konnov, Alexander A.; Alrefae, Majed; Khaled, Fathi; Farooq, Aamir; Dirrenberger, Patricia; Glaude, Pierre Alexandre; Battin-Leclerc, F.; Curran, Henry J.

2015-01-01

Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables. To improve our understanding of the ignition characteristics of propene, a series of IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This work is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2σ) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40. atm) and lower temperatures (750-1750. K).Propene flames were studied at pressures from 1 to 20. atm and unburned gas temperatures of 295-398. K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1. atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (>5. atm).IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good

An experimental and modeling study of propene oxidation. Part 2: Ignition delay time and flame speed measurements

KAUST Repository

Burke, Sinéad M.

2015-02-01

Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables. To improve our understanding of the ignition characteristics of propene, a series of IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This work is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2σ) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40. atm) and lower temperatures (750-1750. K).Propene flames were studied at pressures from 1 to 20. atm and unburned gas temperatures of 295-398. K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1. atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (>5. atm).IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good

Intermediate species measurement during iso-butanol auto-ignition

KAUST Repository

Ji, Weiqi

2015-10-01

© 2015 The Combustion Institute.Published by Elsevier Inc. All rights reserved. This work presents the time histories of intermediate species during the auto-ignition of iso-butanol at high pressure and intermediate temperature conditions obtained using a rapid compression machine and recently developed fast sampling system. Iso-butanol ignition delays were acquired for iso-butanol/O2 mixture with an inert/O2 ratio of 7.26, equivalence ratio of 0.4, in the temperature range of 840-950 K and at pressure of 25 bar. Fast sampling and gas chromatography were used to acquire and quantify the intermediate species during the ignition delay of the same mixture at P = 25.3 bar and T = 905 K. The ignition delay times and quantitative measurements of the mole fraction time histories of methane, ethene, propene, iso-butene, iso-butyraldehyde, iso-butanol, and carbon monoxide were compared with predictions from the detailed mechanisms developed by Sarathy et al., Merchant et al., and Cai et al. It is shown that while the Sarathy mechanism well predicts the overall ignition delay time, it overpredicts ethene by a factor of 6-10, underpredicts iso-butene by a factor of 2, and overpredicts iso-butyraldehyde by a factor of 2. Reaction path and sensitivity analyses were carried out to identify the reactions responsible for the observed inadequacy. The rates of iso-butanol hydrogen atom abstraction by OH radical and the beta-scission reactions of hydroxybutyl radicals were updated based on recently published quantum calculation results. Significant improvements were achieved in predicting ignition delay at high pressures (25 and 30 bar) and the species concentrations of ethene and iso-butene. However, the updated mechanism still overpredicts iso-butyraldehyde concentrations. Also, the updated mechanism degrades the prediction in ignition delay at lower pressure (15 bar) compared to the original mechanism developed by Sarathy et al.

Intermediate species measurement during iso-butanol auto-ignition

KAUST Repository

Ji, Weiqi; Zhang, Peng; He, Tanjin; Wang, Zhi; Tao, Ling; He, Xin; Law, Chung K.

2015-01-01

© 2015 The Combustion Institute.Published by Elsevier Inc. All rights reserved. This work presents the time histories of intermediate species during the auto-ignition of iso-butanol at high pressure and intermediate temperature conditions obtained using a rapid compression machine and recently developed fast sampling system. Iso-butanol ignition delays were acquired for iso-butanol/O2 mixture with an inert/O2 ratio of 7.26, equivalence ratio of 0.4, in the temperature range of 840-950 K and at pressure of 25 bar. Fast sampling and gas chromatography were used to acquire and quantify the intermediate species during the ignition delay of the same mixture at P = 25.3 bar and T = 905 K. The ignition delay times and quantitative measurements of the mole fraction time histories of methane, ethene, propene, iso-butene, iso-butyraldehyde, iso-butanol, and carbon monoxide were compared with predictions from the detailed mechanisms developed by Sarathy et al., Merchant et al., and Cai et al. It is shown that while the Sarathy mechanism well predicts the overall ignition delay time, it overpredicts ethene by a factor of 6-10, underpredicts iso-butene by a factor of 2, and overpredicts iso-butyraldehyde by a factor of 2. Reaction path and sensitivity analyses were carried out to identify the reactions responsible for the observed inadequacy. The rates of iso-butanol hydrogen atom abstraction by OH radical and the beta-scission reactions of hydroxybutyl radicals were updated based on recently published quantum calculation results. Significant improvements were achieved in predicting ignition delay at high pressures (25 and 30 bar) and the species concentrations of ethene and iso-butene. However, the updated mechanism still overpredicts iso-butyraldehyde concentrations. Also, the updated mechanism degrades the prediction in ignition delay at lower pressure (15 bar) compared to the original mechanism developed by Sarathy et al.

Convective Heat Transfer Scaling of Ignition Delay and Burning Rate with Heat Flux and Stretch Rate in the Equivalent Low Stretch Apparatus

Science.gov (United States)

Olson, Sandra

2011-01-01

To better evaluate the buoyant contributions to the convective cooling (or heating) inherent in normal-gravity material flammability test methods, we derive a convective heat transfer correlation that can be used to account for the forced convective stretch effects on the net radiant heat flux for both ignition delay time and burning rate. The Equivalent Low Stretch Apparatus (ELSA) uses an inverted cone heater to minimize buoyant effects while at the same time providing a forced stagnation flow on the sample, which ignites and burns as a ceiling fire. Ignition delay and burning rate data is correlated with incident heat flux and convective heat transfer and compared to results from other test methods and fuel geometries using similarity to determine the equivalent stretch rates and thus convective cooling (or heating) rates for those geometries. With this correlation methodology, buoyant effects inherent in normal gravity material flammability test methods can be estimated, to better apply the test results to low stretch environments relevant to spacecraft material selection.

Two-stage Lagrangian modeling of ignition processes in ignition quality tester and constant volume combustion chambers

KAUST Repository

Alfazazi, Adamu

2016-08-10

The ignition characteristics of isooctane and n-heptane in an ignition quality tester (IQT) were simulated using a two-stage Lagrangian (TSL) model, which is a zero-dimensional (0-D) reactor network method. The TSL model was also used to simulate the ignition delay of n-dodecane and n-heptane in a constant volume combustion chamber (CVCC), which is archived in the engine combustion network (ECN) library (http://www.ca.sandia.gov/ecn). A detailed chemical kinetic model for gasoline surrogates from the Lawrence Livermore National Laboratory (LLNL) was utilized for the simulation of n-heptane and isooctane. Additional simulations were performed using an optimized gasoline surrogate mechanism from RWTH Aachen University. Validations of the simulated data were also performed with experimental results from an IQT at KAUST. For simulation of n-dodecane in the CVCC, two n-dodecane kinetic models from the literature were utilized. The primary aim of this study is to test the ability of TSL to replicate ignition timings in the IQT and the CVCC. The agreement between the model and the experiment is acceptable except for isooctane in the IQT and n-heptane and n-dodecane in the CVCC. The ability of the simulations to replicate observable trends in ignition delay times with regard to changes in ambient temperature and pressure allows the model to provide insights into the reactions contributing towards ignition. Thus, the TSL model was further employed to investigate the physical and chemical processes responsible for controlling the overall ignition under various conditions. The effects of exothermicity, ambient pressure, and ambient oxygen concentration on first stage ignition were also studied. Increasing ambient pressure and oxygen concentration was found to shorten the overall ignition delay time, but does not affect the timing of the first stage ignition. Additionally, the temperature at the end of the first stage ignition was found to increase at higher ambient pressure

Ignition delays, heats of combustion, and reaction rates of aluminum alkyl derivatives used as ignition and combustion enhancers for supersonic combustors

Science.gov (United States)

Ryan, T. W., III; Harlowe, W. W.; Schwab, S.

1992-01-01

The work was based on adapting an apparatus and procedure developed at Southwest Research Institute for rating the ignition quality of fuels for diesel engines. Aluminum alkyls and various Lewis-base adducts of these materials, both neat and mixed 50/50 with pure JP-10 hydrocarbon, were injected into the combustion bomb using a high-pressure injection system. The bomb was pre-charged with air that was set at various initial temperatures and pressures for constant oxygen density. The ignition delay times were determined for the test materials at these different initial conditions. The data are presented in absolute terms as well as comparisons with the parent alkyls. The relative heats of reaction of the various test materials were estimated based on a computation of the heat release, using the pressure data recorded during combustion in the bomb. In addition, the global reaction rates for each material were compared at a selected tmperature and pressure.

Comprehensive study of ignition and combustion of single wooden particles

DEFF Research Database (Denmark)

Momenikouchaksaraei, Maryam; Yin, Chungen; Kær, Søren Knudsen

2013-01-01

How quickly large biomass particles can ignite and burn out when transported into a pulverized-fuel (pf) furnace and suddenly exposed to a hot gas flow containing oxygen is very important in biomass co-firing design and optimization. In this paper, the ignition and burnout of the largest possible...... for all the test conditions. As the particle is further heated up and the volume-weighted average temperature reaches the onset of rapid decomposition of hemicellulose and cellulose, a secondary homogeneous ignition occurs. The model-predicted ignition delays and burnout times show a good agreement...... with the experimental results. Homogeneous ignition delays are found to scale with specific surface areas while heterogeneous ignition delays show less dependency on the areas. The ignition and burnout are also affected by the process conditions, in which the oxygen concentration is found to have a more pronounced...

Study on coal char ignition by radiant heat flux.

Science.gov (United States)

Korotkikh, A. G.; Slyusarskiy, K. V.

2017-11-01

The study on coal char ignition by CO2-continuous laser was carried out. The coal char samples of T-grade bituminous coal and 2B-grade lignite were studied via CO2-laser ignition setup. Ignition delay times were determined at ambient condition in heat flux density range 90-200 W/cm2. The average ignition delay time value for lignite samples were 2 times lower while this difference is larger in high heat flux region and lower in low heat flux region. The kinetic constants for overall oxidation reaction were determined using analytic solution of simplified one-dimensional heat transfer equation with radiant heat transfer boundary condition. The activation energy for lignite char was found to be less than it is for bituminous coal char by approximately 20 %.

Ignition studies of two low-octane gasolines

KAUST Repository

Javed, Tamour

2017-07-24

Low-octane gasolines (RON ∼ 50–70 range) are prospective fuels for gasoline compression ignition (GCI) internal combustion engines. GCI technology utilizing low-octane fuels has the potential to significantly improve well-to-wheel efficiency and reduce the transportation sector\\'s environmental footprint by offsetting diesel fuel usage in compression ignition engines. In this study, ignition delay times of two low-octane FACE (Fuels for Advanced Combustion Engines) gasolines, FACE I and FACE J, were measured in a shock tube and a rapid compression machine over a broad range of engine-relevant conditions (650–1200 K, 20 and 40 bar and ϕ = 0.5 and 1). The two gasolines are of similar octane ratings with anti-knock index, AKI = (RON + MON)/2, of ∼ 70 and sensitivity, S = RON–MON, of ∼ 3. However, the molecular compositions of the two gasolines are notably different. Experimental ignition delay time results showed that the two gasolines exhibited similar reactivity over a wide range of test conditions. Furthermore, ignition delay times of a primary reference fuel (PRF) surrogate (n-heptane/iso-octane blend), having the same AKI as the FACE gasolines, captured the ignition behavior of these gasolines with some minor discrepancies at low temperatures (T < 700 K). Multi-component surrogates, formulated by matching the octane ratings and compositions of the two gasolines, emulated the autoignition behavior of gasolines from high to low temperatures. Homogeneous charge compression ignition (HCCI) engine simulations were used to show that the PRF and multi-component surrogates exhibited similar combustion phasing over a wide range of engine operating conditions.

Comparative Shock-Tube Study of Autoignition and Plasma-Assisted Ignition of C2-Hydrocarbons

Science.gov (United States)

Kosarev, Ilya; Kindysheva, Svetlana; Plastinin, Eugeny; Aleksandrov, Nikolay; Starikovskiy, Andrey

2015-09-01

The dynamics of pulsed picosecond and nanosecond discharge development in liquid water, ethanol and hexane Using a shock tube with a discharge cell, ignition delay time was measured in a lean (φ = 0.5) C2H6:O2:Ar mixture and in lean (φ = 0.5) and stoichiometric C2H4:O2:Ar mixtures with a high-voltage nanosecond discharge and without it. The measured results were compared with the measurements made previously with the same setup for C2H6-, C2H5OH- and C2H2-containing mixtures. It was shown that the effect of plasma on ignition is almost the same for C2H6, C2H4 and C2H5OH. The reduction in time is smaller for C2H2, the fuel that is well ignited even without the discharge. Autoignition delay time was independent of the stoichiometric ratio for C2H6 and C2H4, whereas this time in stoichiometric C2H2- and C2H5OH-containing mixtures was noticeably shorter than that in the lean mixtures. Ignition after the discharge was not affected by a change in the stoichiometric ratio for C2H2 and C2H4, whereas the plasma-assisted ignition delay time for C2H6 and C2H5OH decreased as the equivalence ratio changed from 1 to 0.5. Ignition delay time was calculated in C2-hydrocarbon-containing mixtures under study by simulating separately discharge and ignition processes. Good agreement was obtained between new measurements and calculated ignition delay times.

Experimental and modeling study on effects of N2 and CO2 on ignition characteristics of methane/air mixture

Directory of Open Access Journals (Sweden)

Wen Zeng

2015-03-01

Full Text Available The ignition delay times of methane/air mixture diluted by N2 and CO2 were experimentally measured in a chemical shock tube. The experiments were performed over the temperature range of 1300–2100 K, pressure range of 0.1–1.0 MPa, equivalence ratio range of 0.5–2.0 and for the dilution coefficients of 0%, 20% and 50%. The results suggest that a linear relationship exists between the reciprocal of temperature and the logarithm of the ignition delay times. Meanwhile, with ignition temperature and pressure increasing, the measured ignition delay times of methane/air mixture are decreasing. Furthermore, an increase in the dilution coefficient of N2 or CO2 results in increasing ignition delays and the inhibition effect of CO2 on methane/air mixture ignition is stronger than that of N2. Simulated ignition delays of methane/air mixture using three kinetic models were compared to the experimental data. Results show that GRI_3.0 mechanism gives the best prediction on ignition delays of methane/air mixture and it was selected to identify the effects of N2 and CO2 on ignition delays and the key elementary reactions in the ignition chemistry of methane/air mixture. Comparisons of the calculated ignition delays with the experimental data of methane/air mixture diluted by N2 and CO2 show excellent agreement, and sensitivity coefficients of chain branching reactions which promote mixture ignition decrease with increasing dilution coefficient of N2 or CO2.

Kinetic modeling study of homogeneous ignition of dimethyl ether/hydrogen and dimethyl ether/methane

International Nuclear Information System (INIS)

Wang, Ying; Liu, Hong; Ke, Xichun; Shen, Zhenxing

2017-01-01

Highlights: • Kinetic effects on the homogeneous ignitions of DME/H_2 and DME/CH_4 were studied. • Ignition delays with different DME blending ratio were determined and analyzed. • Different DME ignition combustion trends are found for H_2 and CH_4 addition. • Key elementary reactions are identified at different DME ratios and temperatures. - Abstract: Homogeneous ignition combustion of different proportion DME/H_2 and DME/CH_4 blend fuels in the air is investigated through the numerical simulation with the detailed chemistry at the low and high temperatures in this paper. The emphasis is the assessment of the kinetic effects involved in the ignition combustion of DME/H_2 and DME/CH_4 dual-fuel. It is found that the homogeneous ignition process has a clear distinction at the different temperatures. At the low temperature (900 K), the ignition delay times of DME/H_2 blends and DME/CH_4 blends both show an increase with a decrease of the DME blending ratio; furthermore, it is observed that CH_4 addition is more effective than H_2 addition in terms of delaying the DME homogeneous ignition due to the stable molecular structure of CH_4. At the high temperature (1400 K), with the decrease of DME blending ratio, the ignition delay time of DME/CH_4 blends is still increased, whereas, the ignition delay time of DME/H_2 blends is shortened. Sensitivity analysis, reaction path analysis and main pollutant species calculation are carried out and key elementary reactions involved in homogeneous ignition of DME/H_2 and DME/CH_4 dual fuel are also identified in this paper.

Effects of methyl substitution on the auto-ignition of C16 alkanes

KAUST Repository

Lapuerta, Magín

2015-12-18

The auto-ignition quality of diesel fuels, quantified by their cetane number or derived cetane number (DCN), is a critical design property to consider when producing and upgrading synthetic paraffinic fuels. It is well known that auto-ignition characteristics of paraffinic fuels depend on their degree of methyl substitution. However, there remains a need to study the governing chemical functionalities contributing to such ignition characteristics, especially in the case of methyl substitutions, which have not been studied in detail. In this work, the auto-ignition of 2,6,10-trimethyltridecane has been compared with the reference hydrocarbons used for cetane number determination, i.e. n-hexadecane and heptamethylnonane, all of them being C16 isomers. Results from a constant-volume combustion chamber under different pressure and temperature initial conditions showed that the ignition delay time for both cool flame and main combustion events increased less from n-hexadecane to trimethyltridecane than from trimethyltridecane to heptamethylnonane. Additional experimental results from blends of these hydrocarbons, together with kinetic modelling, showed that auto-ignition times and combustion rates were correlated to the concentration of the functional groups indicative of methyl substitution, although not in a linear manner. When the concentration of these functional groups decreased, the first stage OH radical concentration increased and ignition delay times decreased, whereas when their concentration increased, H2O2 production was slower and ignition was retarded. Contrary to the ignition delay times, DCN was correlated linearly with functional groups, thus homogenizing the range of values and clarifying the differences between fuels.

Effects of methyl substitution on the auto-ignition of C16 alkanes

KAUST Repository

Lapuerta, Magí n; Herná ndez, Juan J.; Sarathy, Mani

2015-01-01

The auto-ignition quality of diesel fuels, quantified by their cetane number or derived cetane number (DCN), is a critical design property to consider when producing and upgrading synthetic paraffinic fuels. It is well known that auto-ignition characteristics of paraffinic fuels depend on their degree of methyl substitution. However, there remains a need to study the governing chemical functionalities contributing to such ignition characteristics, especially in the case of methyl substitutions, which have not been studied in detail. In this work, the auto-ignition of 2,6,10-trimethyltridecane has been compared with the reference hydrocarbons used for cetane number determination, i.e. n-hexadecane and heptamethylnonane, all of them being C16 isomers. Results from a constant-volume combustion chamber under different pressure and temperature initial conditions showed that the ignition delay time for both cool flame and main combustion events increased less from n-hexadecane to trimethyltridecane than from trimethyltridecane to heptamethylnonane. Additional experimental results from blends of these hydrocarbons, together with kinetic modelling, showed that auto-ignition times and combustion rates were correlated to the concentration of the functional groups indicative of methyl substitution, although not in a linear manner. When the concentration of these functional groups decreased, the first stage OH radical concentration increased and ignition delay times decreased, whereas when their concentration increased, H2O2 production was slower and ignition was retarded. Contrary to the ignition delay times, DCN was correlated linearly with functional groups, thus homogenizing the range of values and clarifying the differences between fuels.

Dynamic Regime of Ignition of Solid Propellant

Directory of Open Access Journals (Sweden)

Zolotorev Nikolay

2016-01-01

Full Text Available This article presents a dynamic regime of exposure of the radiant flux on the sample of gun-cotton. Obtained time the ignition of gun-cotton in the heating conditions of increasing heat flux in the range from 0.2 W/cm2 to 22 W/cm2. A comparison of the delay times of the ignition when heated variable and constant heat flux.

Numerical Analysis of the Interaction between Thermo-Fluid Dynamics and Auto-Ignition Reaction in Spark Ignition Engines

Science.gov (United States)

Saijyo, Katsuya; Nishiwaki, Kazuie; Yoshihara, Yoshinobu

The CFD simulations were performed integrating the low-temperature oxidation reaction. Analyses were made with respect to the first auto-ignition location in the case of a premixed-charge compression auto-ignition in a laminar flow field and in the case of the auto-ignition in an end gas during an S. I. Engine combustion process. In the latter simulation, the spatially-filtered transport equations were solved to express fluctuating temperatures in a turbulent flow in consideration of strong non-linearity to temperature in the reaction equations. It is suggested that the first auto-ignition location does not always occur at higher-temperature locations and that the difference in the locations of the first auto-ignition depends on the time period during which the local end gas temperature passes through the region of shorter ignition delay, including the NTC region.

Time-dependent simulations of a Compact Ignition Tokamak

International Nuclear Information System (INIS)

Stotler, D.P.; Bateman, G.

1988-05-01

Detailed simulations of the Compact Ignition Tokamak are carried out using a 1-1/2-D transport code. The calculations include time-varying densities, fields, and plasma shape. It is shown that ignition can be achieved in this device if somewhat better than L-mode energy confinement time scaling is possible. We also conclude that the performance of such a compact, short-pulse device can depend greatly on how the plasma is evolved to its flat-top parameters. Furthermore, in cases such as the ones discussed here, where there is not a great deal of ignition margin and the electron density is held constant, ignition ends if the helium ash is not removed. In general, control of the deuterium--tritium density is equivalent to burn control. 48 refs., 15 figs

Performance Characterization and Auto-Ignition Performance of a Rapid Compression Machine

Directory of Open Access Journals (Sweden)

Hao Liu

2014-09-01

Full Text Available A rapid compression machine (RCM test bench is developed in this study. The performance characterization and auto-ignition performance tests are conducted at an initial temperature of 293 K, a compression ratio of 9.5 to 16.5, a compressed temperature of 650 K to 850 K, a driving gas pressure range of 0.25 MPa to 0.7 MPa, an initial pressure of 0.04 MPa to 0.09 MPa, and a nitrogen dilution ratio of 35% to 65%. A new type of hydraulic piston is used to address the problem in which the hydraulic buffer adversely affects the rapid compression process. Auto-ignition performance tests of the RCM are then performed using a DME–O2–N2 mixture. The two-stage ignition delay and negative temperature coefficient (NTC behavior of the mixture are observed. The effects of driving gas pressure, compression ratio, initial pressure, and nitrogen dilution ratio on the two-stage ignition delay are investigated. Results show that both the first-stage and overall ignition delays tend to increase with increasing driving gas pressure. The driving gas pressure within a certain range does not significantly influence the compressed pressure. With increasing compression ratio, the first-stage ignition delay is shortened, whereas the second-stage ignition delay is extended. With increasing initial pressure, both the first-stage and second-stage ignition delays are shortened. The second-stage ignition delay is shortened to a greater extent than that of the first-stage. With increasing nitrogen dilution ratio, the first-stage ignition delay is shortened, whereas the second-stage is extended. Thus, overall ignition delay presents different trends under various compression ratios and compressed pressure conditions.

Study of ignition in a high compression ratio SI (spark ignition) methanol engine using LES (large eddy simulation) with detailed chemical kinetics

International Nuclear Information System (INIS)

Zhen, Xudong; Wang, Yang

2013-01-01

Methanol has been recently used as an alternative to conventional fuels for internal combustion engines in order to satisfy some environmental and economical concerns. In this paper, the ignition in a high compression ratio SI (spark ignition) methanol engine was studied by using LES (large eddy simulation) with detailed chemical kinetics. A 21-species, 84-reaction methanol mechanism was adopted to simulate the auto-ignition process of the methanol/air mixture. The MIT (minimum ignition temperature) and MIE (minimum ignition energy) are two important properties for designing safety standards and understanding the ignition process of combustible mixtures. The effects of the flame kernel size, flame kernel temperature and equivalence ratio were also examined on MIT, MIE and IDP (ignition delay period). The methanol mechanism was validated by experimental test. The simulated results showed that the flame kernel size, temperature and energy dramatically affected the values of the MIT, MIE and IDP for a methanol/air mixture, the value of the ignition delay period was not only related to the flame kernel energy, but also to the flame kernel temperature. - Highlights: • We used LES (large eddy simulation) coupled with detailed chemical kinetics to simulate methanol ignition. • The flame kernel size and temperature affected the minimum ignition temperature. • The flame kernel temperature and energy affected the ignition delay period. • The equivalence ratio of methanol–air mixture affected the ignition delay period

Shock Timing Plan for the National Ignition Campaign

Science.gov (United States)

Munro, D. H.; Robey, H. F.; Spears, B. K.; Boehly, T. R.

2006-10-01

We report progress on the design of the shock timing tuning procedure for the 2010 ignition campaign at the National Ignition Facility. Our keyhole target design provides adequate drive surrogacy for us to time the first three shocks empirically. The major risk to our plan is hard x-ray preheat, which can cause the diagnostic window to become opaque.

Ignition of a floating droplet of organic coal-water fuel

Science.gov (United States)

Nakoryakov, V. E.; Kuznetsov, G. V.; Strizhak, P. A.

2016-06-01

The results of experimental investigations are presented for the ignition of droplets (particles) of organic coal-water fuels (OCWFs) floating in a flow of an oxidizer using a special combustion chamber from high-temperature quartz glass. The temperature and the velocity of motion of the oxidizer vary in the ranges of 500-900 K and 0.5-3 m/s. The initial sizes (radii) of fuel droplets amounted to 0.3-1.5 mm. As the basic OCWF components, particles (of 80-100 µm in size) of brown coal "B2," water, mazut, and waste castor and compressor oils are used. With use of the system of high-velocity video registration, the conditions providing for floating of OCWF particles without initiation of burning and with the subsequent steady ignition are established. Four modes of OCWF-droplet ignition with different trajectories of their motion in the combustion chamber are singled out. The times of the OCWF-ignition delay in dependence on the size of fuel particles and oxidizer temperatures are determined. The deviations of the OCWF-ignition-delay times obtained under conditions of suspension of a droplet on the thermocouple junction and while floating in the oxidizer flow are established.

The combustion chemistry of a fuel tracer: Measured flame speeds and ignition delays and a detailed chemical kinetic model for the oxidation of acetone

Energy Technology Data Exchange (ETDEWEB)

Pichon, S.; Black, G.; Simmie, J.M.; Curran, H.J. [Combustion Chemistry Centre, National University of Ireland, Galway (Ireland); Chaumeix, N.; Yahyaoui, M. [Institut de Combustion Aerothermique Reactivite et Environnement, CNRS, Orleans (France); Donohue, R. [Information Technology, National University of Ireland, Galway (Ireland)

2009-02-15

Acetone ignition delay and stretch-free laminar flame speed measurements have been carried out and a kinetic model has been developed to simulate these and literature data for acetone and for ketene, which was found to be an important intermediate in its oxidation. The mechanism has been based on one originally devised for dimethyl ether and modified through validation of the hydrogen, carbon monoxide and methane sub-mechanisms. Acetone oxidation in argon was studied behind reflected shock waves in the temperature range 1340-1930 K, at 1 atm and at equivalence ratios of 0.5, 1 and 2; it is also shown that the addition of up to 15% acetone to a stoichiometric n-heptane mixture has no effect on the measured ignition delay times. Flame speeds at 298 K and 1 atm of pure acetone in air were measured in a spherical bomb; a maximum flame speed of {proportional_to}35 cm s{sup -1} at {phi}=1.15 is indicated. (author)

Flow Effects on the Flammability Diagrams of Solid Fuels: Microgravity Influence on Ignition Delay

Science.gov (United States)

Cordova, J. L.; Walther, D. C.; Fernandez-Pello, A. C.; Steinhaus, T.; Torero, J. L.; Quintere, J. G.; Ross, H. D.

1999-01-01

The possibility of an accidental fire in space-based facilities is a primary concern of space exploration programs. Spacecraft environments generally present low velocity air currents produced by ventilation and heating systems (of the order of 0.1 m/s), and fluctuating oxygen concentrations around that of air due to CO2 removal systems. Recent experiments of flame spread in microgravity show the spread rate to be faster and the limiting oxygen concentration lower than in normal-gravity. To date, there is not a material flammability-testing protocol that specifically addresses issues related to microgravity conditions. The present project (FIST) aims to establish a testing methodology that is suitable for the specific conditions of reduced gravity. The concepts underlying the operation of the LIFT apparatus, ASTM-E 1321-93, have been used to develop the Forced-flow Ignition and flame-Spread Test (FIST). As in the LIFT, the FIST is used to obtain the flammability diagrams of the material, i.e., graphs of ignition delay time and flame spread rate as a function of the externally applied radiant flux, but under forced flow rather than natural convection conditions, and for different oxygen concentrations. Although the flammability diagrams are similar, the flammability properties obtained with the FIST are found to depend on the flow characteristics. A research program is currently underway with the purpose of implementing the FIST as a protocol to characterize the flammability performance of solid materials to be used in microgravity facilities. To this point, tests have been performed with the FIST apparatus in both normal-gravity and microgravity conditions to determine the effects of oxidizer flow characteristics on the flammability diagrams of polymethylmethacrylate (PMMA) fuel samples. The experiments are conducted at reduced gravity in a KC- 135 aircraft following a parabolic flight trajectory that provides up to 25 seconds of low gravity. The objective of the

Energy cascading by triple-bubble interactions via time-delayed control

International Nuclear Information System (INIS)

Lin, Yen-Liang; Chang, Chia-Ming; Tseng, Fan-Gang; Yang, I-Da; Chieng, Ching-Chang

2012-01-01

The triple-bubble interaction controlled by a precise time-delayed technique was investigated in detail with respect to different ignition times, heater spaces and sequential firing modes to promote efficient energy cascading and concentration. The target bubble, which was generated under a specific delay time with two auxiliary bubbles, can have a volume that is two or almost three times larger than that of a single bubble. This result overcomes the limitation of energy usage on an explosive microbubble under a constant heat flux. As the heater space decreases, stronger bubble–bubble interactions were obtained due to the hydrodynamic effect and the intensive pressure wave emission, resulting in highly enhancing and depressing bubble dynamics. Other interesting phenomena, such as bubble shifting, mushroom-shape bubble, rod-shape bubble and bubble extension among heaters, were also recorded by a high-speed phase-averaged stroboscopic technique, displaying special non-spherical bubble dynamics. Artificial manipulation of bubble behavior was further conducted in a two-level sequential firing process. Using various volumetric combinations, the adjustable multi-level fluid transportation can be realized by a digital time-delayed control. The above-mentioned information can be applied to not only the design and operation of inkjet printheads but also cavitation research and fluid pumping in microdevices. (paper)

Ignition of a Droplet of Composite Liquid Fuel in a Vortex Combustion Chamber

Science.gov (United States)

Valiullin, T. R.; Vershinina, K. Yu; Glushkov, D. O.; Strizhak, P. A.

2017-11-01

Experimental study results of a droplet ignition and combustion were obtained for coal-water slurry containing petrochemicals (CWSP) prepared from coal processing waste, low-grade coal and waste petroleum products. A comparative analysis of process characteristics were carried out in different conditions of fuel droplet interaction with heated air flow: droplet soars in air flow in a vortex combustion chamber, droplet soars in ascending air flow in a cone-shaped combustion chamber, and droplet is placed in a thermocouple junction and motionless in air flow. The size (initial radii) of CWSP droplet was varied in the range of 0.5-1.5 mm. The ignition delay time of fuel was determined by the intensity of the visible glow in the vicinity of the droplet during CWSP combustion. It was established (under similar conditions) that ignition delay time of CWSP droplets in the combustion chamber is lower in 2-3.5 times than similar characteristic in conditions of motionless droplet placed in a thermocouple junction. The average value of ignition delay time of CWSP droplet is 3-12 s in conditions of oxidizer temperature is 600-850 K. Obtained experimental results were explained by the influence of heat and mass transfer processes in the droplet vicinity on ignition characteristics in different conditions of CWSP droplet interaction with heated air flow. Experimental results are of interest for the development of combustion technology of promising fuel for thermal power engineering.

Ignition characteristics of 2-methyltetrahydrofuran: An experimental and kinetic study

KAUST Repository

Tripathi, Rupali

2016-10-15

The present paper elucidates oxidation behavior of 2-methyltetrahydrofuran (2-MTHF), a novel second-generation biofuel. New experimental data sets for 2-MTHF including ignition delay time measurements in two different combustion reactors, i.e. rapid compression machine and high-pressure shock tube, are presented. Measurements for 2-MTHF/oxidizer/diluent mixtures were performed in the temperature range of . 639-1413 K, at pressures of 10, 20, and 40 bar, and at three different equivalence ratios of 0.5, 1.0, and 2.0. A detailed chemical kinetic model describing both low-and high-temperature chemistry of 2-MTHF was developed and validated against new ignition delay measurements and already existing flame species profiles and ignition delay measurements. The mechanism provides satisfactory agreement with the experimental data. For identifying key reactions at various combustion conditions and to attain a better understanding of the combustion behavior, reaction path and sensitivity analyses were performed.

Chemical kinetics modeling of the influence of molecular structure on shock tube ignition delay

International Nuclear Information System (INIS)

Westbrook, C.K.; Pitz, W.J.

1985-07-01

The current capabilities of kinetic modeling of hydrocarbon oxidation in shock waves are discussed. The influence of molecular size and structure on ignition delay times are stressed. The n-paraffin fuels from CH 4 to n-C 5 H 12 are examined under shock tube conditions, as well as the branched chain fuel isobutane, and the computed results are compared with available experimental data. The modeling results show that it is important in the reaction mechanism to distinguish between abstraction of primary, secondary and tertiary H atom sites from the fuel molecule. This is due to the fact that both the rates and the product distributions of the subsequent alkyl radical decomposition reactions depend on which H atoms were abstracted. Applications of the reaction mechanisms to shock tube problems and to other practical problems such as engine knock are discussed

Ignition in net for different energy confinement time scalings

International Nuclear Information System (INIS)

Johner, J.; Prevot, F.

1988-06-01

A zero-dimensional profile dependent model is used to assess the feasibility of ignition in the extended version of NET. Five recent scalings for the energy confinement time (Goldston, Kaye All, Kaye Big, Shimomura-Odajima, Rebut-Lallia) are compared in the frame of two different scenarii, i.e., H-mode with a flat density profile or L-mode with a peaked density profile. For the flat density H-mode case, ignition is accessible with none of the scalings except Rebut-Lallia's. For the peaked density L-mode case, ignition is accessible with none of the scalings except Rebut-Lallia's. For the two Kaye's scalings, ignition is forbidden in H-mode even with the peaked density profile. For the Rebut-Lallia scaling, ignition is allowed in L-mode even with the flat density profile

Analytical solutions for prediction of the ignition time of wood particles based on a time and space integral method

International Nuclear Information System (INIS)

Haseli, Y.; Oijen, J.A. van; Goey, L.P.H. de

2012-01-01

Highlights: ► A simple model for prediction of the ignition time of a wood particle is presented. ► The formulation is given for both thermally thin and thermally thick particles. ► Transition from thermally thin to thick regime occurs at a critical particle size. ► The model is validated against a numerical model and various experimental data. - Abstract: The main idea of this paper is to establish a simple approach for prediction of the ignition time of a wood particle assuming that the thermo-physical properties remain constant and ignition takes place at a characteristic ignition temperature. Using a time and space integral method, explicit relationships are derived for computation of the ignition time of particles of three common shapes (slab, cylinder and sphere), which may be characterized as thermally thin or thermally thick. It is shown through a dimensionless analysis that the dimensionless ignition time can be described as a function of non-dimensional ignition temperature, reactor temperature or external incident heat flux, and parameter K which represents the ratio of conduction heat transfer to the external radiation heat transfer. The numerical results reveal that for the dimensionless ignition temperature between 1.25 and 2.25 and for values of K up to 8000 (corresponding to woody materials), the variation of the ignition time of a thermally thin particle with K and the dimensionless ignition temperature is linear, whereas the dependence of the ignition time of a thermally thick particle on the above two parameters obeys a quadratic function. Furthermore, it is shown that the transition from the regime of thermally thin to the regime of thermally thick occurs at K cr (corresponding to a critical size of particle) which is found to be independent of the particle shape. The model is validated by comparing the predicted and the measured ignition time of several wood particles obtained from different sources. Good agreement is achieved which

Shock timing technique for the National Ignition Facility

International Nuclear Information System (INIS)

Munro, David H.; Celliers, Peter M.; Collins, Gilbert W.; Gold, David M.; Silva, Luiz B. da; Haan, Steven W.; Cauble, Robert C.; Hammel, Bruce A.; Hsing, Warren W.

2001-01-01

Among the final shots at the Nova laser [Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)] was a series testing the VISAR (velocity interferometry system for any reflector) technique that will be the primary diagnostic for timing the shocks in a NIF (National Ignition Facility) ignition capsule. At Nova, the VISAR technique worked over the range of shock strengths and with the precision required for the NIF shock timing job--shock velocities in liquid D 2 from 12 to 65 μm/ns with better than 2% accuracy. VISAR images showed stronger shocks overtaking weaker ones, which is the basis of the plan for setting the pulse shape for the NIF ignition campaign. The technique is so precise that VISAR measurements may also play a role in certifying beam-to-beam and shot-to-shot repeatability of NIF laser pulses

Ignition of alkane-rich FACE gasoline fuels and their surrogate mixtures

KAUST Repository

Sarathy, Mani

2015-01-01

Petroleum derived gasoline is the most used transportation fuel for light-duty vehicles. In order to better understand gasoline combustion, this study investigated the ignition propensity of two alkane-rich FACE (Fuels for Advanced Combustion Engines) gasoline test fuels and their corresponding PRF (primary reference fuel) blend in fundamental combustion experiments. Shock tube ignition delay times were measured in two separate facilities at pressures of 10, 20, and 40 bar, temperatures from 715 to 1500 K, and two equivalence ratios. Rapid compression machine ignition delay times were measured for fuel/air mixtures at pressures of 20 and 40 bar, temperatures from 632 to 745 K, and two equivalence ratios. Detailed hydrocarbon analysis was also performed on the FACE gasoline fuels, and the results were used to formulate multi-component gasoline surrogate mixtures. Detailed chemical kinetic modeling results are presented herein to provide insights into the relevance of utilizing PRF and multi-component surrogate mixtures to reproduce the ignition behavior of the alkane-rich FACE gasoline fuels. The two FACE gasoline fuels and their corresponding PRF mixture displayed similar ignition behavior at intermediate and high temperatures, but differences were observed at low temperatures. These trends were mimicked by corresponding surrogate mixture models, except for the amount of heat release in the first stage of a two-stage ignition events, when observed. © 2014 The Combustion Institute.

Effects of In-Cylinder Mixing on Low Octane Gasoline Compression Ignition Combustion

KAUST Repository

Badra, Jihad; Farooq, Aamir; Sim, Jaeheon; Viollet, Yoann; Im, Hong G.; Chang, Junseok

2016-01-01

Gasoline compression ignition (GCI) engines have been considered an attractive alternative to traditional spark ignition engines. Low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and in the volatility range of gasoline fuels. In this study, we have investigated the effect of different injection timings at part-load conditions using light naphtha stream in single cylinder engine experiments in the GCI combustion mode with injection pressure of 130 bar. A toluene primary reference fuel (TPRF) was used as a surrogate for the light naphtha in the engine simulations performed here. A physical surrogate based on the evaporation characteristics of the light naphtha has been developed and its properties have been implemented in the engine simulations. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from -50° to -11 ° CAD aTDC. The effect of SOI on mixing and combustion phasing was investigated using detailed equivalence ratio-temperature maps and ignition delay times. Both experimental and computational results consistently showed that an SOI of -30° CAD aTDC has the most advanced combustion phasing (CA50), with the highest NOx emission. The effects of the SOI on the fuel containment in the bowl of the piston, the ignition delay time, combustion rate and emissions have been carefully examined through the CFD calculations. It was found that the competition between the equivalence ratio and temperature is the controlling parameter in determining the combustion phasings.

Effects of In-Cylinder Mixing on Low Octane Gasoline Compression Ignition Combustion

KAUST Repository

Badra, Jihad

2016-04-05

Gasoline compression ignition (GCI) engines have been considered an attractive alternative to traditional spark ignition engines. Low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and in the volatility range of gasoline fuels. In this study, we have investigated the effect of different injection timings at part-load conditions using light naphtha stream in single cylinder engine experiments in the GCI combustion mode with injection pressure of 130 bar. A toluene primary reference fuel (TPRF) was used as a surrogate for the light naphtha in the engine simulations performed here. A physical surrogate based on the evaporation characteristics of the light naphtha has been developed and its properties have been implemented in the engine simulations. Full cycle GCI computational fluid dynamics (CFD) engine simulations have been successfully performed while changing the start of injection (SOI) timing from -50° to -11 ° CAD aTDC. The effect of SOI on mixing and combustion phasing was investigated using detailed equivalence ratio-temperature maps and ignition delay times. Both experimental and computational results consistently showed that an SOI of -30° CAD aTDC has the most advanced combustion phasing (CA50), with the highest NOx emission. The effects of the SOI on the fuel containment in the bowl of the piston, the ignition delay time, combustion rate and emissions have been carefully examined through the CFD calculations. It was found that the competition between the equivalence ratio and temperature is the controlling parameter in determining the combustion phasings.

Fuel octane effects in the partially premixed combustion regime in compression ignition engines

NARCIS (Netherlands)

Hildingsson, L.; Kalghatgi, G.T.; Tait, N.; Johansson, B.H.; Harrison, A.

2009-01-01

Previous work has showed that it may be advantageous to use fuels of lower cetane numbers compared to today's diesel fuels in compression ignition engines. The benefits come from the longer ignition delays that these fuels have. There is more time available for the fuel and air to mix before

Energy confinement time and tokamak ignition - a theoretical viewpoint

International Nuclear Information System (INIS)

Sigmar, D.J.; Hsu, C.T.

1989-01-01

A rigorous approach developed earlier to obtain the global energy confinement time from theory based local thermal transport coefficients is applied to investigate the approach to thermonuclear fusion in the tokamak. Theory leads naturally to a generalized 'offset' form for the global energy confinement time. The limitations of the theoretical paradigm presented here are discussed and specific ignition contour results for a large 5 Tesla and 12 Tesla ignition experiment are given. (orig.) [de

Tokamak power reactor ignition and time dependent fractional power operation

International Nuclear Information System (INIS)

Vold, E.L.; Mau, T.K.; Conn, R.W.

1986-06-01

A flexible time-dependent and zero-dimensional plasma burn code with radial profiles was developed and employed to study the fractional power operation and the thermal burn control options for an INTOR-sized tokamak reactor. The code includes alpha thermalization and a time-dependent transport loss which can be represented by any one of several currently popular scaling laws for energy confinement time. Ignition parameters were found to vary widely in density-temperature (n-T) space for the range of scaling laws examined. Critical ignition issues were found to include the extent of confinement time degradation by alpha heating, the ratio of ion to electron transport power loss, and effect of auxiliary heating on confinement. Feedback control of the auxiliary power and ion fuel sources are shown to provide thermal stability near the ignition curve

Ignition of Coal Dust from the Tomsk Region Talovsky Deposit by Air Flow

Directory of Open Access Journals (Sweden)

Chebochakova Diana A.

2015-01-01

Full Text Available This paper focuses on the experimental studies of the ignition characteristics of brown coal dust particles from the Tomsk region Talovsky deposit under the conditions of convective heating. The boundary conditions of combustion initiation have been established. The approximation dependence of ignition delay time from the temperature of a heat source has been found.

Ignition characteristics of 2-methyltetrahydrofuran: An experimental and kinetic study

KAUST Repository

Tripathi, Rupali; Lee, Changyoul; Fernandes, Ravi X.; Olivier, Herbert; Curran, Henry J.; Sarathy, Mani; Pitsch, Heinz

2016-01-01

The present paper elucidates oxidation behavior of 2-methyltetrahydrofuran (2-MTHF), a novel second-generation biofuel. New experimental data sets for 2-MTHF including ignition delay time measurements in two different combustion reactors, i.e. rapid

Chaos synchronization in time-delayed systems with parameter mismatches and variable delay times

International Nuclear Information System (INIS)

Shahverdiev, E.M.; Nuriev, R.A.; Hashimov, R.H.; Shore, K.A.

2004-06-01

We investigate synchronization between two undirectionally linearly coupled chaotic nonidentical time-delayed systems and show that parameter mismatches are of crucial importance to achieve synchronization. We establish that independent of the relation between the delay time in the coupled systems and the coupling delay time, only retarded synchronization with the coupling delay time is obtained. We show that with parameter mismatch or without it neither complete nor anticipating synchronization occurs. We derive existence and stability conditions for the retarded synchronization manifold. We demonstrate our approach using examples of the Ikeda and Mackey Glass models. Also for the first time we investigate chaos synchronization in time-delayed systems with variable delay time and find both existence and sufficient stability conditions for the retarded synchronization manifold with the coupling-delay lag time. (author)

Variable valve timing in a homogenous charge compression ignition engine

Science.gov (United States)

Lawrence, Keith E.; Faletti, James J.; Funke, Steven J.; Maloney, Ronald P.

2004-08-03

The present invention relates generally to the field of homogenous charge compression ignition engines, in which fuel is injected when the cylinder piston is relatively close to the bottom dead center position for its compression stroke. The fuel mixes with air in the cylinder during the compression stroke to create a relatively lean homogeneous mixture that preferably ignites when the piston is relatively close to the top dead center position. However, if the ignition event occurs either earlier or later than desired, lowered performance, engine misfire, or even engine damage, can result. The present invention utilizes internal exhaust gas recirculation and/or compression ratio control to control the timing of ignition events and combustion duration in homogeneous charge compression ignition engines. Thus, at least one electro-hydraulic assist actuator is provided that is capable of mechanically engaging at least one cam actuated intake and/or exhaust valve.

Analytical solutions for prediction of the ignition time of wood particles based on a time and space integral method

NARCIS (Netherlands)

Haseli, Y.; Oijen, van J.A.; Goey, de L.P.H.

2012-01-01

The main idea of this paper is to establish a simple approach for prediction of the ignition time of a wood particle assuming that the thermo-physical properties remain constant and ignition takes place at a characteristic ignition temperature. Using a time and space integral method, explicit

Ignition timing advance in the bi-fuel engine

Directory of Open Access Journals (Sweden)

Marek FLEKIEWICZ

2009-01-01

Full Text Available The influence of ignition timing on CNG combustion process has been presented in this paper. A 1.6 liter SI engine has been tested in the special program. For selected engine operating conditions, following data were acquired: in cylinder pressure, crank angle, fuel mass consumption and exhaust gases temperatures. For the timing advance correction varying between 0 to 15 deg crank angle, the internal temperature of combustion chamber, as well as the charge combustion ratio and ratio of heat release has been estimated. With the help of the mathematical model, emissions of NO, CO and CO2 were additionally estimated. Obtained results made it possible to compare the influence of ignition timing advance on natural gas combustion in the SI engine. The engine torque and in-cylinder pressure were used for determination of the optimum engine timing advance.

Shock timing on the National Ignition Facility: First Experiments

International Nuclear Information System (INIS)

Celliers, P.M.; Robey, H.F.; Boehly, T.R.; Alger, E.; Azevedo, S.; Berzins, L.V.; Bhandarkar, S.D.; Bowers, M.W.; Brereton, S.J.; Callahan, D.; Castro, C.; Chandrasekaran, H.; Choate, C.; Clark, D.; Coffee, K.R.; Datte, P.S.; Dewald, E.L.; DiNicola, P.; Dixit, S.; Doeppner, T.; Dzenitis, E.; Edwards, M.J.; Eggert, J.H.; Fair, J.; Farley, D.R.; Frieders, G.; Gibson, C.R.; Giraldez, E.; Haan, S.; Haid, B.; Hamza, A.V.; Haynam, C.; Hicks, D.G.; Holunga, D.M.; Horner, J.B.; Jancaitis, K.; Jones, O.S.; Kalantar, D.; Kline, J.L.; Krauter, K.G.; Kroll, J.J.; LaFortune, K.N.; Pape, S.L.; Malsbury, T.; Maypoles, E.R.; Milovich, J.L.; Moody, J.D.; Moreno, K.; Munro, D.H.; Nikroo, A.; Olson, R.E.; Parham, T.; Pollaine, S.; Radousky, H.B.; Ross, G.F.; Sater, J.; Schneider, M.B.; Shaw, M.; Smith, R.F.; Thomas, C.A.; Throop, A.; Town, R.J.; Trummer, D.; Van Wonterghem, B.M.; Walters, C.F.; Widmann, K.; Widmayer, C.; Young, B.K.; Atherton, L.J.; Collins, G.W.; Landen, O.L.; Lindl, J.D.; MacGowan, B.J.; Meyerhofer, D.D.; Moses, E.I.

2011-01-01

An experimental campaign to tune the initial shock compression sequence of capsule implosions on the National Ignition Facility (NIF) was initiated in late 2010. The experiments use a NIF ignition-scale hohlraum and capsule that employs a reentrant cone to provide optical access to the shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of the shock sequence is diagnosed with velocity interferometry that provides target performance data used to set the pulse shape for ignition capsule implosions that follow. From the start, these measurements yielded significant new information on target performance, leading to improvements in the target design. We describe the results and interpretation of the initial tuning experiments.

Global synchronization criteria with channel time-delay for chaotic time-delay system

International Nuclear Information System (INIS)

Sun Jitao

2004-01-01

Based on the Lyapunov stabilization theory, matrix measure, and linear matrix inequality (LMIs), this paper studies the chaos synchronization of time-delay system using the unidirectional linear error feedback coupling with time-delay. Some generic conditions of chaos synchronization with time-delay in the transmission channel is established. The chaotic Chua's circuit is used for illustration, where the coupling parameters are determined according to the criteria under which the global chaos synchronization of the time-delay coupled systems is achieved

Ignition of alkane-rich FACE gasoline fuels and their surrogate mixtures

KAUST Repository

Sarathy, Mani; Kukkadapu, Goutham; Mehl, Marco; Wang, Weijing; Javed, Tamour; Park, Sungwoo; Oehlschlaeger, Matthew A.; Farooq, Aamir; Pitz, William J.; Sung, Chihjen

2015-01-01

Engines) gasoline test fuels and their corresponding PRF (primary reference fuel) blend in fundamental combustion experiments. Shock tube ignition delay times were measured in two separate facilities at pressures of 10, 20, and 40 bar, temperatures from

Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms

Science.gov (United States)

Starikovskaia, S. M.

2014-09-01

This review covers the results obtained in the period 2006-2014 in the field of plasma-assisted combustion, and in particular the results on ignition and combustion triggered or sustained by pulsed nanosecond discharges in different geometries. Some benefits of pulsed high voltage discharges for kinetic study and for applications are demonstrated. The necessity of and the possibility of building a particular kinetic mechanism of plasma-assisted ignition and combustion are discussed. The most sensitive regions of parameters for plasma-combustion kinetic mechanisms are selected. A map of the pressure and temperature parameters (P-T diagram) is suggested, to unify the available data on ignition delay times, ignition lengths and densities of intermediate species reported by different authors.

Shock timing on the National Ignition Facility: First experiments

Directory of Open Access Journals (Sweden)

Celliers P.M.

2013-11-01

Full Text Available An experimental campaign to tune the initial shock compression sequence of capsule implosions on the National Ignition Facility (NIF was initiated in late 2010. The experiments use a NIF ignition-scale hohlraum and capsule that employs a re-entrant cone to provide optical access to the shocks as they propagate in the liquid deuterium-filled capsule interior. The strength and timing of the shock sequence is diagnosed with velocity interferometry that provides target performance data used to set the pulse shape for ignition capsule implosions that follow. From the start, these measurements yielded significant new information on target performance, leading to improvements in the target design. We describe the results and interpretation of the initial tuning experiments.

Auto-ignitions of a methane/air mixture at high and intermediate temperatures

Science.gov (United States)

Leschevich, V. V.; Martynenko, V. V.; Penyazkov, O. G.; Sevrouk, K. L.; Shabunya, S. I.

2016-09-01

A rapid compression machine (RCM) and a shock tube (ST) have been employed to study ignition delay times of homogeneous methane/air mixtures at intermediate-to-high temperatures. Both facilities allow measurements to be made at temperatures of 900-2000 K, at pressures of 0.38-2.23 MPa, and at equivalence ratios of 0.5, 1.0, and 2.0. In ST experiments, nitrogen served as a diluent gas, whereas in RCM runs the diluent gas composition ranged from pure nitrogen to pure argon. Recording pressure, UV, and visible emissions identified the evolution of chemical reactions. Correlations of ignition delay time were generated from the data for each facility. At temperatures below 1300 K, a significant reduction of average activation energy from 53 to 15.3 kcal/mol was obtained. Moreover, the RCM data showed significant scatter that dramatically increased with decreasing temperature. An explanation for the abnormal scatter in the data was proposed based on the high-speed visualization of auto-ignition phenomena and experiments performed with oxygen-free and fuel-free mixtures. It is proposed that the main reason for such a significant reduction of average activation energy is attributable to the premature ignition of ultrafine particles in the reactive mixture.

Fast-shock ignition: a new approach to inertial confinement fusion

Directory of Open Access Journals (Sweden)

AH Farahbod

2013-03-01

Full Text Available  A new concept for inertial confinement fusion called fast-shock ignition (FSI is introduced as a credible scheme in order to obtain high target gain. In the proposed model, the separation of fuel ignition into two successive steps, under the suitable conditions, reduces required ignitor energy for the fuel ignition. The main procedure in FSI concept is compressing the fuel up to stagnation. Then, two high intensity short pulse laser spikes with energy and power lower than those required for shock ignition (SI and fast ignition (FI with a proper delay time are launched at the fuel which increases the central hot-spot temperature and completes the ignition of the precompressed fuel. The introduced semi-analytical model indicates that with fast-shock ignition, the total required energy for compressing and igniting the fuel can be slightly reduced in comparison to pure shock ignition. Furthermore, for fuel mass greater than , the target energy gain increases up to 15 percent and the contribution of fast ignitor under the proper conditions could be decreased about 20 percent compared with pure fast ignition. The FSI scheme is beneficial from technological considerations for the construction of short pulse high power laser drivers. The general advantages of fast-shock ignition over pure shock ignition in terms of figure of merit can be more than 1.3.

Experimental study of the form of "hot" steel particles on the ignition characteristics of liquid fuels

Science.gov (United States)

Zakharevich, Arkadiy V.

2015-01-01

The results of an experimental study of laws governing the ignition of liquid propellants (kerosene, diesel fuel and petroleum residue) by the single spherical steel particle heated to high temperatures are presented. Is carried out the comparison of the ignition delay times of the investigated flammable substances by the particles in the sphere and disk forms. It is established that the particle shape does not exert a substantial influence on the ignition process characteristics.

Optimum injection and combustion for gaseous fuel engine : characteristics of hydrogen auto-ignition phenomena

Energy Technology Data Exchange (ETDEWEB)

Tsujimura, T.; Mikami, S.; Senda, J.; Fujimoto, H. [Doshisha Univ. (Japan). Dept. of Mechanical Engineering; Nakatani, K. [Fuji Heavy Industries Ltd. (Japan); Tokunaga, Y. [Kawasaki Heavy Industries Ltd. (Japan)

2002-07-01

A study was conducted in which the auto-ignition characteristics of hydrogen were examined in order to determine which factors dominate auto-ignition delay of hydrogen jets. Experiments were performed in a rapid compression/expansion machine in order to study the effects of ambient gas density and oxygen concentration on the auto-ignition delays. The focus of research was on an inert gas circulation type cogeneration system to apply hydrogen to a medium-sized diesel engine. Freedom of fuel-oxidizer mixing, ignition and combustion in the system could be achieved for stable combustion, high thermal efficiency, and zero emission. The study also involved chemical analysis using a detailed hydrogen reaction model that could simulate auto-ignition delays under various temperature, pressures, equivalence ratio, and dilution. It is shown that auto-ignition delays of hydrogen jets are very dependent on the ambient gas temperature and less dependent on its density and oxygen concentration. Temperature and hydrogen concentrations have significant impacts on the production and consumption rates of H{sub 2}O{sub 2} and OH radicals. 21 refs., 1 tab., 10 figs.

TOPICAL REVIEW: Plasma assisted ignition and combustion

Science.gov (United States)

Starikovskaia, S. M.

2006-08-01

In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

High-Gain Shock Ignition on the National Ignition Facility

Science.gov (United States)

Perkins, L. J.; Lafortune, K.; Bailey, D.; Lambert, M.; MacKinnon, A.; Blackfield, D.; Comley, A.; Schurtz, G.; Ribeyre, X.; Lebel, E.; Casner, A.; Craxton, R. S.; Betti, R.; McKenty, P.; Anderson, K.; Theobald, W.; Schmitt, A.; Atzeni, S.; Schiavi, A.

2010-11-01

Shock ignition offers the possibility for a near-term test of high-gain ICF on the NIF at less than 1MJ drive energy and with day-1 laser hardware. We will summarize the status of target performance simulations, delineate the critical issues and describe the R&D program to be performed in order to test the potential of a shock-ignited target on NIF. In shock ignition, compressed fuel is separately ignited by a late-time laser-driven shock and, because capsule implosion velocities are significantly lower than those required for conventional hotpot ignition, simulations indicate that fusion energy gains of 60 may be achievable at laser energies around 0.5MJ. Like fast ignition, shock ignition offers high gain but requires only a single laser with less demanding timing and focusing requirements. Conventional symmetry and stability constraints apply, thus a key immediate step towards attempting shock ignition on NIF is to demonstrate adequacy of low-mode uniformity and shock symmetry under polar drive

Effect of Timing and Location of Hotspot on Super Knock during Pre-ignition

KAUST Repository

Jaasim, Mohammed

2017-03-28

Pre-ignition in SI engine is a critical issue that needs addressing as it may lead to super knock event. It is widely accepted that pre-ignition event emanates from hot spot(s) that can be anywhere inside the combustion chamber. The location and timing of hotspot is expected to influence the knock intensity from a pre-ignition event. In this study, we study the effect of location and timing of hot spot inside the combustion chamber using numerical simulations. The simulation is performed using a three-dimensional computational fluid dynamics (CFD) code, CONVERGE™. We simulate 3-D engine geometry coupled with chemistry, turbulence and moving structures (valves, piston). G-equation model for flame tracking coupled with multi-zone model is utilized to capture auto-ignition (knock) and solve gas phase kinetics. A parametric study on the effect of hot spot timing and location inside the combustion chamber is performed. The hot spot timing considered are -180 CAD, -90 CAD and -30 CAD and the locations of the hot spots are in the center and two edges of the piston surfaces. Simulation results for normal combustion cycle are validated against the experimental data. The simulation results show great sensitivity to the hot spot timing, and the influence of local temperature gradient is noted to be significant. In case of early hot spot timing of -180 CAD, the pre-ignition event did not lead to super knock. Nevertheless, at late hot spot timing, super knock was realized. On the other hand, the effect of hot spot location on pre-ignition event depends on the geometry of the combustion chamber.

Communication key using delay times in time-delayed chaos synchronization

International Nuclear Information System (INIS)

Kim, Chil-Min; Kye, Won-Ho; Rim, Sunghwan; Lee, Soo-Young

2004-01-01

We propose an efficient key scheme, which can generate a great number of communication keys, for communication using chaos synchronization. We have attained the keys from delay times of time-delay coupled chaotic systems. We explain the scheme and the efficiency by coupling Henon and logistic maps and illustrate them by coupling Navier-Stokes and Lorenz equations as a continuous system

Analysis of the Effect of Injection Pressure on Ignition Delay and Combustion Process of Biodiesel from Palm Oil, Algae and Waste Cooking Oil

Science.gov (United States)

Irham Anas, Mohd; Khalid, Amir; Hakim Zulkifli, Fathul; Jaat, Norrizam; Faisal Hushim, Mohd; Manshoor, Bukhari; Zaman, Izzuddin

2017-10-01

Biodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant grease for use in diesel engines. The objective of this research is investigation the effects of the variant injection pressure on ignition delay and emission for different biodiesel using rapid compression machine. Rapid Compression Machine (RCM) is used to simulate a single compression stroke of an internal combustion engine as a real engine. Four types of biodiesel which are waste cooking oil, crude palm oil, algae and jatropha were tested at injection pressure of 80 MPa, 90 MPa and 130 MPa under constant ambient temperature at 950 K. Increased in injection pressure resulted shorter ignition delay proven by WCO5 which decreased from 1.3 ms at 80 MPa to 0.7 ms at 130 MPa. Meanwhile, emission for CO2 increased due to better fuel atomization for fuel-air mixture formation lead to completed combustion.

Experimental study of the form of “hot” steel particles on the ignition characteristics of liquid fuels

Directory of Open Access Journals (Sweden)

Zakharevich Arkadiy V.

2015-01-01

Full Text Available The results of an experimental study of laws governing the ignition of liquid propellants (kerosene, diesel fuel and petroleum residue by the single spherical steel particle heated to high temperatures are presented. Is carried out the comparison of the ignition delay times of the investigated flammable substances by the particles in the sphere and disk forms. It is established that the particle shape does not exert a substantial influence on the ignition process characteristics.

Investigation of Spark Ignition and Autoignition in Methane and Air Using Computational Fluid Dynamics and Chemical Reaction Kinetics. A numerical Study of Ignition Processes in Internal Combustion Engines

Energy Technology Data Exchange (ETDEWEB)

Nordrik, R.

1993-12-01

The processes in the combustion chamber of internal combustion engines have received increased attention in recent years because their efficiencies are important both economically and environmentally. This doctoral thesis studies the ignition phenomena by means of numerical simulation methods. The fundamental physical relations include flow field conservation equations, thermodynamics, chemical reaction kinetics, transport properties and spark modelling. Special attention is given to the inclusion of chemical kinetics in the flow field equations. Using his No Transport of Radicals Concept method, the author reduces the computational efforts by neglecting the transport of selected intermediate species. The method is validated by comparison with flame propagation data. A computational method is described and used to simulate spark ignition in laminar premixed methane-air mixtures and the autoignition process of a methane bubble surrounded by hot air. The spark ignition simulation agrees well with experimental results from the literature. The autoignition simulation identifies the importance of diffusive and chemical processes acting together. The ignition delay times exceed the experimental values found in the literature for premixed ignition delay, presumably because of the mixing process and lack of information on low temperature reactions in the skeletal kinetic mechanism. Transient turbulent methane jet autoignition is simulated by means of the KIVA-II code. Turbulent combustion is modelled by the Eddy Dissipation Concept. 90 refs., 81 figs., 3 tabs.

Information transfer via implicit encoding with delay time modulation in a time-delay system

Energy Technology Data Exchange (ETDEWEB)

Kye, Won-Ho, E-mail: whkye@kipo.go.kr [Korean Intellectual Property Office, Government Complex Daejeon Building 4, 189, Cheongsa-ro, Seo-gu, Daejeon 302-701 (Korea, Republic of)

2012-08-20

A new encoding scheme for information transfer with modulated delay time in a time-delay system is proposed. In the scheme, the message is implicitly encoded into the modulated delay time. The information transfer rate as a function of encoding redundancy in various noise scales is presented and it is analyzed that the implicit encoding scheme (IES) has stronger resistance against channel noise than the explicit encoding scheme (EES). In addition, its advantages in terms of secure communication and feasible applications are discussed. -- Highlights: ► We propose new encoding scheme with delay time modulation. ► The message is implicitly encoded with modulated delay time. ► The proposed scheme shows stronger resistance against channel noise.

Ignition and devolatilization of pulverized coals in lower oxygen content O{sub 2}/CO{sub 2} atmosphere

Energy Technology Data Exchange (ETDEWEB)

Huang, Xiaohong; Li, Jing; Liu, Zhaohui; Yang, Ming; Wang, Dingbang; Zheng, Chuguang [Huazhong Univ. of Science and Technology, Wuhan (China). State Key Lab. of Coal Combustion

2013-07-01

High speed camera is employed to capture the transient images of the burning particle in a flat-flame entrained flow reactor, some information of the burning particle, such as the optical intensity and the residence time, are obtained through analysis of transient images. The ignition and devolatilization behavior of different rank coals at 1,670, 1,770 and 1,940 K over a range of 2-30% O{sub 2} in both N{sub 2} and CO{sub 2} diluent gases are researched. The results indicate that the laws of ignition and devolatilization of pulverized coals in low oxygen O{sub 2}/CO{sub 2} atmosphere are consistent with the literature, which focus on the environments of high oxygen contents (10-30%) or lower temperate (900-1,500 K). With the gas temperature and oxygen content increased, the ignition delay time and devolatilization time for the lower oxygen content cases decreased for both N{sub 2} and CO{sub 2} atmosphere. With the use CO{sub 2} in place of N{sub 2} in low oxygen content, the ignition delay was retarded and the duration of devolatilization was increased. The effect of CO{sub 2} on coal particle ignition is explained by its higher molar specific heat. And the effect of CO{sub 2} on devolatilization results from its effect on the diffusion rates of volatile fuel and oxygen.

Investigation of the ignition of liquid hydrocarbon fuels with nanoadditives

Science.gov (United States)

Bakulin, V. N.; Velikodnyi, V. Yu.; Levin, Yu. K.; Popov, V. V.

2017-12-01

During our experimental studies we showed a high efficiency of the influence of nanoparticle additives on the stability of the ignition of hydrocarbon fuels and the stabilization of their combustion in a highfrequency high-voltage discharge. We detected the effects of a jet deceleration, an increase in the volume of the combustible mixture, and a reduction in the inflammation delay time. These effects have been estimated quantitatively by digitally processing the video frames of the ignition of a bubbled kerosene jet with 0.5% graphene nanoparticle additives and without these additives. This effect has been explained by the influence of electrodynamic processes.

Chemical kinetic insights into the ignition dynamics of n-hexane

KAUST Repository

Tingas, Alexandros

2017-10-13

Normal alkanes constitute a significant fraction of transportation fuels, and are the primary drivers of ignition processes in gasoline and diesel fuels. Low temperature ignition of n-alkanes is driven by a complex sequence of oxidation reactions, for which detailed mechanisms are still being developed. The current study explores the dynamics of low-temperature ignition of n-hexane/air mixtures, and identifies chemical pathways that characterize the combustion process. Two chemical kinetic mechanisms were selected as a comparative study in order to better understand the role of specific reaction sequences in ignition dynamics: one mechanism including a new third sequential O2 addition reaction pathways (recently proposed by Wang et al. 2017), while the other without (Zhang et al. 2015). The analysis is conducted by applying tools generated from the computational singular perturbation (CSP) approach to two distinct ignition phenomena: constant volume and compression ignition. In both cases, the role of the third sequential O2 addition reactions proves to be significant, although it is found to be much more pronounced in the constant volume cases compared to the HCCI. In particular, in the constant volume ignition case, reactions present in the third sequential O2 addition reaction pathways (e.g., KDHP  →  products + OH) contribute significantly to the explosivity of the mixture; when accounted for along with reactions P(OOH)2 + O2  →  OOP(OOH)2 and OOP(OOH)2  →  KDHP + OH, they decrease ignition delay time of the mixture by up to 40%. Under HCCI conditions, in the first-stage ignition, the third-O2 addition reactions contribute to the process, although their role decays with time and becomes negligible at the end of the first stage. The second ignition stage is dominated almost exclusively by hydrogen-related chemistry.

On the effect of injection timing on the ignition of lean PRF/air/EGR mixtures under direct dual fuel stratification conditions

KAUST Repository

Luong, Minh Bau; Sankaran, Ramanan; Yu, Gwang Hyeon; Chung, Suk-Ho; Yoo, Chun Sang

2017-01-01

The ignition characteristics of lean primary reference fuel (PRF)/air/exhaust gas recirculation (EGR) mixture under reactivity-controlled compression ignition (RCCI) and direct duel fuel stratification (DDFS) conditions are investigated by 2-D direct numerical simulations (DNSs) with a 116-species reduced chemistry of the PRF oxidation. The 2-D DNSs of the DDFS combustion are performed by varying the injection timing of iso-octane (i-C8H18) with a pseudo-iso-octane (PC8H18) model together with a novel compression heating model to account for the compression heating and expansion cooling effects of the piston motion in an engine cylinder. The PC8H18 model is newly developed to mimic the timing, duration, and cooling effects of the direct injection of i-C8H18 onto a premixed background charge of PRF/air/EGR mixture with composition inhomogeneities. It is found that the RCCI combustion exhibits a very high peak heat release rate (HRR) with a short combustion duration due to the predominance of the spontaneous ignition mode of combustion. However, the DDFS combustion has much lower peak HRR and longer combustion duration regardless of the fuel injection timing compared to those of the RCCI combustion, which is primarily attributed to the sequential injection of i-C8H18. It is also found that the ignition delay of the DDFS combustion features a non-monotonic behavior with increasing fuel-injection timing due to the different effect of fuel evaporation on the low-, intermediate-, and high-temperature chemistry of the PRF oxidation. The budget and Damköhler number analyses verify that although a mixed combustion mode of deflagration and spontaneous ignition exists during the early phase of the DDFS combustion, the spontaneous ignition becomes predominant during the main combustion, and hence, the spread-out of heat release rate in the DDFS combustion is mainly governed by the direct injection process of i-C8H18. Finally, a misfire is observed for the DDFS combustion when

On the effect of injection timing on the ignition of lean PRF/air/EGR mixtures under direct dual fuel stratification conditions

KAUST Repository

Luong, Minh Bau

2017-06-10

The ignition characteristics of lean primary reference fuel (PRF)/air/exhaust gas recirculation (EGR) mixture under reactivity-controlled compression ignition (RCCI) and direct duel fuel stratification (DDFS) conditions are investigated by 2-D direct numerical simulations (DNSs) with a 116-species reduced chemistry of the PRF oxidation. The 2-D DNSs of the DDFS combustion are performed by varying the injection timing of iso-octane (i-C8H18) with a pseudo-iso-octane (PC8H18) model together with a novel compression heating model to account for the compression heating and expansion cooling effects of the piston motion in an engine cylinder. The PC8H18 model is newly developed to mimic the timing, duration, and cooling effects of the direct injection of i-C8H18 onto a premixed background charge of PRF/air/EGR mixture with composition inhomogeneities. It is found that the RCCI combustion exhibits a very high peak heat release rate (HRR) with a short combustion duration due to the predominance of the spontaneous ignition mode of combustion. However, the DDFS combustion has much lower peak HRR and longer combustion duration regardless of the fuel injection timing compared to those of the RCCI combustion, which is primarily attributed to the sequential injection of i-C8H18. It is also found that the ignition delay of the DDFS combustion features a non-monotonic behavior with increasing fuel-injection timing due to the different effect of fuel evaporation on the low-, intermediate-, and high-temperature chemistry of the PRF oxidation. The budget and Damköhler number analyses verify that although a mixed combustion mode of deflagration and spontaneous ignition exists during the early phase of the DDFS combustion, the spontaneous ignition becomes predominant during the main combustion, and hence, the spread-out of heat release rate in the DDFS combustion is mainly governed by the direct injection process of i-C8H18. Finally, a misfire is observed for the DDFS combustion when

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

Energy Technology Data Exchange (ETDEWEB)

Milovich, J. L., E-mail: milovich1@llnl.gov; Dewald, E. L.; Pak, A.; Michel, P.; Town, R. P. J.; Bradley, D. K.; Landen, O.; Edwards, M. J. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)

2016-03-15

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P{sub 2}), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

International Nuclear Information System (INIS)

Milovich, J. L.; Dewald, E. L.; Pak, A.; Michel, P.; Town, R. P. J.; Bradley, D. K.; Landen, O.; Edwards, M. J.

2016-01-01

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or “picket”) period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P_2), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the “Rev5” CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using

Early-time radiation flux symmetry optimization and its effect on gas-filled hohlraum ignition targets on the National Ignition Facility

Science.gov (United States)

Milovich, J. L.; Dewald, E. L.; Pak, A.; Michel, P.; Town, R. P. J.; Bradley, D. K.; Landen, O.; Edwards, M. J.

2016-03-01

Achieving ignition on the National Ignition Facility (NIF) is tied to our ability to control and minimize deviations from sphericity of the capsule implosion. Low-mode asymmetries of the hot spot result from the combined effect of radiation drive asymmetries throughout the laser pulse and initial roughness on the capsule surface. In this paper, we report on simulations and experiments designed to assess, measure, and correct the drive asymmetries produced by the early-time (≈first 2 ns or "picket") period of the laser pulse. The drive asymmetry during the picket is commonly thought to introduce distortions in the hot-spot shape at ignition time. However, a more subtle effect not previously considered is that it also leads to an asymmetry in shock velocity and timing, thereby increasing the fuel adiabat and reducing the margin for ignition. It is shown via hydrodynamic simulations that minimizing this effect requires that the early-time asymmetry be kept below 7.5% in the second Legendre mode (P2), thus keeping the loss of performance margin below ≈10% for a layered implosion. Asymmetries during the picket of the laser pulse are measured using the instantaneous self-emission of a high-Z re-emission sphere in place of an ignition capsule in a hohlraum with large azimuthal diagnostic windows. Three dimensional simulations using the code HYDRA (to capture the effect of non-azimuthal hohlraum features) coupled to a cross-beam energy transfer model [Michel et al., Phys. Plasmas 17, 056305 (2010)] are used to establish the surrogacy of the re-emit target and to assess the early-time drive symmetry. Calculations using this model exhibit the same sensitivity to variations in the relative input powers between the different cones of NIF beams as measured for the "Rev5" CH target [Haan et al., Phys Plasmas 18, 051001 (2011)] and reported by Dewald et al. [Phys. Rev. Lett. 111, 235001 (2013)]. The same methodology applied to recently improved implosions using different

Ignition and fusion burn in fast ignition scheme

International Nuclear Information System (INIS)

Takabe, Hideaki

1998-01-01

The target physics of fast ignition is briefly reviewed by focusing on the ignition and fusion burn in the off-center ignition scheme. By the use of a two dimensional hydrodynamic code with an alpha heating process, the ignition condition is studied. It is shown that the ignition condition of the off-center ignition scheme coincides with that of the the central isochoric model. After the ignition, a nuclear burning wave is seen to burn the cold main fuel with a velocity of 2 - 3 x 10 8 cm/s. The spark energy required for the off-center ignition is 2 - 3 kJ or 10 - 15 kJ for the core density of 400 g/cm 3 or 200 g/cm 3 , respectively. It is demonstrated that a core gain of more than 2,000 is possible for a core energy of 100 kJ with a hot spark energy of 13 kJ. The requirement for the ignition region's heating time is also discussed by modeling a heating source in the 2-D code. (author)

Laser-assisted ignition and combustion characteristics of consolidated aluminum nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Saceleanu, Florin; Wen, John Z., E-mail: john.wen@uwaterloo.ca [University of Waterloo, Department of Mechanical and Mechatronics Engineering (Canada); Idir, Mahmoud; Chaumeix, Nabiha [Institut de Combustion, Aérothermique, Réactivité et Environnement, UPR3021 du CNRS-INSIS (France)

2016-11-15

Aluminum (Al) nanoparticles have drawn much attention due to their high energy density and tunable ignition properties. In comparison with their micronscale counterpart, Al nanoparticles possess large specific surface area and low apparent activation energy of combustion, which reduce ignition delay significantly. In this paper, ignition and subsequently burning of consolidated Al nanoparticle pellets are performed via a continuous wave (CW) argon laser in a closed spherical chamber filled with oxygen. Pellets are fabricated using two types of nanoparticle sizes of 40–60 and 60–80 nm, respectively. A photodiode is used to measure the ignition delay, while a digital camera captures the location of the flame front. It is found that for the 40–60-nm nanoparticle pellets, ignition delay reduces with increasing the oxygen pressure or using the higher laser power. Analysis of the flame propagation rate suggests that oxygen diffusion is an important mechanism during burning of these porous nanoparticle pellets. The combustion characteristics of the Al pellets are compared to a simplified model of the diffusion-controlled oxidation mechanism. While experimental measurements of pellets of 40–60 nm Al particles agree with the computed diffusion-limiting mechanism, a shifted behavior is observed from the pellets of 60–80 nm Al particles, largely due to the inhomogeneity of their porous structures.

The ignition of magnesium and magnox alloys. A review of data

International Nuclear Information System (INIS)

Pearce, R.J.

1987-07-01

Available data on the ignition temperatures of magnesium and the Magnox alloys of interest in CEGB Magnox reactor operations have been reviewed. Two basic ignition modes, instantaneous where a continuing and high rate of temperature rise is applied to the metal and delayed where the metal is held at a predetermined ambient temperature until ignition occurs, are identified. (author)

49 CFR 236.563 - Delay time.

Science.gov (United States)

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Delay time. 236.563 Section 236.563 Transportation... Cab Signal Systems Rules and Instructions; Locomotives § 236.563 Delay time. Delay time of automatic... requirements of § 236.24 shall take into consideration the delay time. ...

Direct numerical simulations of ignition of a lean n-heptane/air mixture with temperature and composition inhomogeneities relevant to HCCI and SCCI combustion

KAUST Repository

Luong, Minh Bau

2015-12-01

The effects of temperature and composition stratifications on the ignition of a lean n-heptane/air mixture at three initial mean temperatures under elevated pressure are investigated using direct numerical simulations (DNSs) with a 58-species reduced mechanism. Two-dimensional DNSs are performed by varying several key parameters: initial mean temperature, T0, and the variance of temperature and equivalence ratio (T\\' and φ\\') with different T-φcorrelations. It is found that for cases with φ\\' only, the overall combustion occurs more quickly and the mean heat release rate (HRR) increases more slowly with increasing φ\\' regardless of T0. For cases with T\\' only, however, the overall combustion is retarded/advanced in time with increasing T\\' for low/high T0 relative to the negative-temperature coefficient (NTC) regime resulting from a longer/shorter overall ignition delay of the mixture. For cases with uncorrelated T-φfields, the mean HRR is more distributed over time compared to the corresponding cases with T\\' or φ\\' only. For negatively-correlated cases, however, the temporal evolution of the overall combustion exhibits quite non-monotonic behavior with increasing T\\' and φ\\' depending on T0. All of these characteristics are found to be primarily related to the 0-D ignition delays of initial mixtures, the relative timescales between 0-D ignition delay and turbulence, and the dominance of the deflagration mode during the ignition. These results suggest that an appropriate combination of T\\' and φ\\' together with a well-prepared T-φdistribution can alleviate an excessive pressure-rise rate (PRR) and control ignition-timing in homogeneous charge compression-ignition (HCCI) combustion. In addition, critical species and reactions for the ignition of n-heptane/air mixture through the whole ignition process are estimated by comparing the temporal evolution of the mean mass fractions of important species with the overall reaction pathways of n

Time Delay of CGM Sensors

Science.gov (United States)

Schmelzeisen-Redeker, Günther; Schoemaker, Michael; Kirchsteiger, Harald; Freckmann, Guido; Heinemann, Lutz; del Re, Luigi

2015-01-01

Background: Continuous glucose monitoring (CGM) is a powerful tool to support the optimization of glucose control of patients with diabetes. However, CGM systems measure glucose in interstitial fluid but not in blood. Rapid changes in one compartment are not accompanied by similar changes in the other, but follow with some delay. Such time delays hamper detection of, for example, hypoglycemic events. Our aim is to discuss the causes and extent of time delays and approaches to compensate for these. Methods: CGM data were obtained in a clinical study with 37 patients with a prototype glucose sensor. The study was divided into 5 phases over 2 years. In all, 8 patients participated in 2 phases separated by 8 months. A total number of 108 CGM data sets including raw signals were used for data analysis and were processed by statistical methods to obtain estimates of the time delay. Results: Overall mean (SD) time delay of the raw signals with respect to blood glucose was 9.5 (3.7) min, median was 9 min (interquartile range 4 min). Analysis of time delays observed in the same patients separated by 8 months suggests a patient dependent delay. No significant correlation was observed between delay and anamnestic or anthropometric data. The use of a prediction algorithm reduced the delay by 4 minutes on average. Conclusions: Prediction algorithms should be used to provide real-time CGM readings more consistent with simultaneous measurements by SMBG. Patient specificity may play an important role in improving prediction quality. PMID:26243773

Laser ignitibility of insensitive secondary explosive 1,1-diamino-2,2-dinitroethene (FOX-7)

International Nuclear Information System (INIS)

Fang, Xiao; McLuckie, Warren G

2015-01-01

Highlights: • Carbon black (CB) is an efficient optical sensitizer compatible with 1,1-diamino-2,2-dinitroethene (FOX-7). • A CB doped insensitive explosive FOX-7 can be ignited by a low-power diode laser. • Laser ignitibility of the optically sensitized FOX-7 is mainly affected by laser power among the other parameters. • Inhomogeneities in the explosive affect laser ignition reliability. - Abstract: An experimental investigation into laser ignitibility of insensitive secondary explosives, 1,1-diamino-2,2-dinitroethene (FOX-7) has been carried out, using a diode laser of continuous wave at the laser wavelength of 974 nm. The direct optical ignition of an insensitive explosive will add more safety features to insensitive munitions (IM) or explosive devices. In this study, effects of laser parameters on the ignitibility were analysed in terms of laser ignition threshold, the times to initiate the ignition and full combustion, and burning sustainability. The results have shown that carbon black (CB) as an optical sensitizer is compatible with FOX-7, and significantly enhances laser ignitibility of the explosive when a small amount of CB is uniformly doped in FOX-7. The delay times for ignition and subsequent development of sustainable burning of the material are mainly determined by ignition laser power, although the other laser parameters have effects. The minimum laser power required to ignite the optically sensitized FOX-7 was found below 10 W and a fast ignition was initiated in as short as 70 μs by a laser power of 40 W. Also the effect of the mixture uniformity of FOX-7/CB on laser ignition performance was evaluated in this study

Memorized discrete systems and time-delay

CERN Document Server

Luo, Albert C J

2017-01-01

This book examines discrete dynamical systems with memory—nonlinear systems that exist extensively in biological organisms and financial and economic organizations, and time-delay systems that can be discretized into the memorized, discrete dynamical systems. It book further discusses stability and bifurcations of time-delay dynamical systems that can be investigated through memorized dynamical systems as well as bifurcations of memorized nonlinear dynamical systems, discretization methods of time-delay systems, and periodic motions to chaos in nonlinear time-delay systems. The book helps readers find analytical solutions of MDS, change traditional perturbation analysis in time-delay systems, detect motion complexity and singularity in MDS; and determine stability, bifurcation, and chaos in any time-delay system.

Experimental Investigation of Augmented Spark Ignition of a LO2/LCH4 Reaction Control Engine at Altitude Conditions

Science.gov (United States)

Kleinhenz, Julie; Sarmiento, Charles; Marshall, William

2012-01-01

The use of nontoxic propellants in future exploration vehicles would enable safer, more cost-effective mission scenarios. One promising green alternative to existing hypergols is liquid methane (LCH4) with liquid oxygen (LO2). A 100 lbf LO2/LCH4 engine was developed under the NASA Propulsion and Cryogenic Advanced Development project and tested at the NASA Glenn Research Center Altitude Combustion Stand in a low pressure environment. High ignition energy is a perceived drawback of this propellant combination; so this ignition margin test program examined ignition performance versus delivered spark energy. Sensitivity of ignition to spark timing and repetition rate was also explored. Three different exciter units were used with the engine s augmented (torch) igniter. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks. This suggests that rising pressure and flow rate increase spark impedance and may at some point compromise an exciter s ability to complete each spark. The reduced spark energies of such quenched deliveries resulted in more erratic ignitions, decreasing ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1 to 6 mJ, though multiple, similarly timed sparks of 55 to 75 mJ were required for reliable ignition. Delayed spark application and reduced spark repetition rate both correlated with late and occasional failed ignitions. An optimum time interval for spark application and ignition therefore coincides with propellant introduction to the igniter.

Ignition and combustion of pyrotechnics at low pressures and at temperature extremes

Directory of Open Access Journals (Sweden)

Clive Woodley

2017-06-01

Full Text Available Rapid and effective ignition of pyrotechnic countermeasure decoy flares is vitally important to the safety of expensive military platforms such as aircraft. QinetiQ is conducting experimental and theoretical research into pyrotechnic countermeasure decoy flares. A key part of this work is the development and application of improved models to increase the understanding of the ignition processes occurring for these flares. These models have been implemented in a two-dimensional computational model and details are described in this paper. Previous work has conducted experiments and validated the computational model at ambient temperature and pressure. More recently the computational model has been validated at pressures down to that equivalent to 40,000 feet but at ambient temperature (∼290 K. This paper describes further experimental work in which the ignition delays of the priming material in inert countermeasure decoy flares were determined for pressures down to 40,000 feet and at temperature extremes of −40 °C and 100 °C. Also included in this paper is a comparison of the measured and predicted ignition delays at low pressures and temperature extremes. The agreement between the predicted and measured ignition delays is acceptable.

Diethyl Ether as an Ignition Enhancer for Naphtha Creating a Drop in Fuel for Diesel

KAUST Repository

Vallinayagam, R.

2016-12-01

Direct use of naphtha in compression ignition (CI) engines is not advisable because its lower cetane number negatively impacts the auto ignition process. However, engine or fuel modifications can be made to operate naphtha in CI engines. Enhancing a fuel’s auto ignition characteristics presents an opportunity to use low cetane fuel, naphtha, in CI engines. In this research, Di-ethyl ether (DEE) derived from ethanol is used as an ignition enhancer for light naphtha. With this fuel modification, a “drop-in” fuel that is interchangeable with existing diesel fuel has been created. The ignition characteristics of DEE blended naphtha were studied in an ignition quality tester (IQT); the measured ignition delay time (IDT) for pure naphtha was 6.9 ms. When DEE was added to naphtha, IDT decreased and D30 (30% DEE + 70% naphtha) showed comparable IDT with US NO.2 diesel. The derived cetane number (DCN) of naphtha, D10 (10% DEE + 90% naphtha), D20% DEE + 80% naphtha) and D30 were measured to be 31, 37, 40 and 49, respectively. The addition of 30% DEE in naphtha achieved a DCN equivalent to US NO.2 diesel. Subsequent experiments in a CI engine exhibited longer ignition delay for naphtha compared to diesel. The peak in-cylinder pressure is higher for naphtha than diesel and other tested fuels. When DEE was added to naphtha, the ignition delay shortened and peak in-cylinder pressure is reduced. A 3.7% increase in peak in-cylinder pressure was observed for naphtha compared to US NO.2 diesel, while D30 showed comparable results with diesel. The pressure rise rate dropped with the addition of DEE to naphtha, thereby reducing the ringing intensity. Naphtha exhibited a peak heat release rate of 280 kJ/m3deg, while D30 showed a comparable peak heat release rate to US NO.2 diesel. The amount of energy released during the premixed combustion phase decreased with the increase of DEE in naphtha. Thus, this study demonstrates the suitability of DEE blended naphtha mixtures as a �

Diethyl Ether as an Ignition Enhancer for Naphtha Creating a Drop in Fuel for Diesel

KAUST Repository

Vallinayagam, R.; Vedharaj, S.; Sarathy, Mani; Dibble, Robert W.

2016-01-01

Direct use of naphtha in compression ignition (CI) engines is not advisable because its lower cetane number negatively impacts the auto ignition process. However, engine or fuel modifications can be made to operate naphtha in CI engines. Enhancing a fuel’s auto ignition characteristics presents an opportunity to use low cetane fuel, naphtha, in CI engines. In this research, Di-ethyl ether (DEE) derived from ethanol is used as an ignition enhancer for light naphtha. With this fuel modification, a “drop-in” fuel that is interchangeable with existing diesel fuel has been created. The ignition characteristics of DEE blended naphtha were studied in an ignition quality tester (IQT); the measured ignition delay time (IDT) for pure naphtha was 6.9 ms. When DEE was added to naphtha, IDT decreased and D30 (30% DEE + 70% naphtha) showed comparable IDT with US NO.2 diesel. The derived cetane number (DCN) of naphtha, D10 (10% DEE + 90% naphtha), D20% DEE + 80% naphtha) and D30 were measured to be 31, 37, 40 and 49, respectively. The addition of 30% DEE in naphtha achieved a DCN equivalent to US NO.2 diesel. Subsequent experiments in a CI engine exhibited longer ignition delay for naphtha compared to diesel. The peak in-cylinder pressure is higher for naphtha than diesel and other tested fuels. When DEE was added to naphtha, the ignition delay shortened and peak in-cylinder pressure is reduced. A 3.7% increase in peak in-cylinder pressure was observed for naphtha compared to US NO.2 diesel, while D30 showed comparable results with diesel. The pressure rise rate dropped with the addition of DEE to naphtha, thereby reducing the ringing intensity. Naphtha exhibited a peak heat release rate of 280 kJ/m3deg, while D30 showed a comparable peak heat release rate to US NO.2 diesel. The amount of energy released during the premixed combustion phase decreased with the increase of DEE in naphtha. Thus, this study demonstrates the suitability of DEE blended naphtha mixtures as a �

Effect of Hydrogen Addition on Methane HCCI Engine Ignition Timing and Emissions Using a Multi-zone Model

Science.gov (United States)

Wang, Zi-han; Wang, Chun-mei; Tang, Hua-xin; Zuo, Cheng-ji; Xu, Hong-ming

2009-06-01

Ignition timing control is of great importance in homogeneous charge compression ignition engines. The effect of hydrogen addition on methane combustion was investigated using a CHEMKIN multi-zone model. Results show that hydrogen addition advances ignition timing and enhances peak pressure and temperature. A brief analysis of chemical kinetics of methane blending hydrogen is also performed in order to investigate the scope of its application, and the analysis suggests that OH radical plays an important role in the oxidation. Hydrogen addition increases NOx while decreasing HC and CO emissions. Exhaust gas recirculation (EGR) also advances ignition timing; however, its effects on emissions are generally the opposite. By adjusting the hydrogen addition and EGR rate, the ignition timing can be regulated with a low emission level. Investigation into zones suggests that NOx is mostly formed in core zones while HC and CO mostly originate in the crevice and the quench layer.

Robust Moving Horizon H∞ Control of Discrete Time-Delayed Systems with Interval Time-Varying Delays

Directory of Open Access Journals (Sweden)

F. Yıldız Tascikaraoglu

2014-01-01

Full Text Available In this study, design of a delay-dependent type moving horizon state-feedback control (MHHC is considered for a class of linear discrete-time system subject to time-varying state delays, norm-bounded uncertainties, and disturbances with bounded energies. The closed-loop robust stability and robust performance problems are considered to overcome the instability and poor disturbance rejection performance due to the existence of parametric uncertainties and time-delay appeared in the system dynamics. Utilizing a discrete-time Lyapunov-Krasovskii functional, some delay-dependent linear matrix inequality (LMI based conditions are provided. It is shown that if one can find a feasible solution set for these LMI conditions iteratively at each step of run-time, then we can construct a control law which guarantees the closed-loop asymptotic stability, maximum disturbance rejection performance, and closed-loop dissipativity in view of the actuator limitations. Two numerical examples with simulations on a nominal and uncertain discrete-time, time-delayed systems, are presented at the end, in order to demonstrate the efficiency of the proposed method.

Numerical parametric investigations of a gasoline fuelled partially-premixed compression-ignition engine

Energy Technology Data Exchange (ETDEWEB)

Nemati, Arash [Islamic Azad University, Miyaneh Branch, Miyaneh (Iran, Islamic Republic of); Khalilarya, Shahram; Jafarmadar, Samad; Khatamenjhad, Hassan [Department of Mechanical Engineering, Urmia University, Urmia (Iran, Islamic Republic of); Fathi, Vahid [Islamic Azad University, Ajagshir Branch, Ajabshir (Iran, Islamic Republic of)

2011-07-01

Parametric studies of a heavy duty direct injection (DI) gasoline fueled compression ignition (CI) engine combustion are presented. Gasoline because of its higher ignition delay has much lower soot emission in comparison with diesel fuel. Using double injection strategy reduces the maximum heat release rate that leads to nitrogen oxides (NOx) emission reduction. A three dimensional computational fluid dynamics (CFD) code was employed and compared with experimental data. The model results show a good agreement with experimental data. The effect of injection characteristics such as, injection duration, main SOI timing, and nozzle hole size investigated on combustion and emissions.

Laser ignition of DAAF, DHT and DAATO{sub 3.5}

Energy Technology Data Exchange (ETDEWEB)

Ali, Arif N.; Sandstrom, Mary M.; Oschwald, David M.; Moore, Kevin M.; Son, Steven F. [Los Alamos National Laboratory, Los Alamos, NM 87544 (United States)

2005-10-01

CO{sub 2} laser ignition experimental results are reported for the high-nitrogen materials 3,6-dihydrazino-1,2,4,5-tetrazine (DHT), 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and mixed N-oxides of 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO{sub 3.5}, where the ''3.5'' indicates the average oxide content) at a maximum irradiance level of approximately 140 W/cm{sup 2}. Diagnostics include a photodiode, indium antimonide (InSb) IR detector, high speed (HS) video and a CO{sub 2} photodetector. ''First light'' is measured for DAATO{sub 3.5} and DAAF, however, due to the low visible light emission of the gas phase, thermal runaway, as measured by the InSb, is used as the ignition criterion for DHT. Ignition in the gas phase is captured by the high speed camera. It is observed that an increase in laser irradiance results in an increase in ignition and flame stand-off distance for DAATO{sub 3.5}. The high-nitrogen material laser ignition results are compared to the common nitramine explosive, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Laser ignition delays for the different high-nitrogen materials are also compared in the context of Differential Scanning Calorimetry (DSC) data. It is determined that DSC onset temperature, while a rough indicator of ignition delay trends, is not the equivalent of a direct measure of ignition temperature. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

Dopant-induced ignition of helium nanoplasmas—a mechanistic study

Science.gov (United States)

Heidenreich, Andreas; Schomas, Dominik; Mudrich, Marcel

2017-12-01

Helium (He) nanodroplets irradiated by intense near-infrared laser pulses form a nanoplasma by avalanche-like electron impact ionizations (EIIs) even at lower laser intensities where He is not directly field ionized, provided that the droplets contain a few dopant atoms which provide seed electrons for the EII avalanche. In this theoretical paper on calcium and xenon doped He droplets we elucidate the mechanism which induces ionization avalanches, termed ignition. We find that the partial loss of seed electrons from the activated droplets starkly assists ignition, as the Coulomb barrier for ionization of helium is lowered by the electric field of the dopant cations, and this deshielding of the cation charges enhances their electric field. In addition, the dopant ions assist the acceleration of the seed electrons (slingshot effect) by the laser field, supporting EIIs of He and also causing electron loss by catapulting electrons away. The dopants’ ability to lower the Coulomb barriers at He as well as the slingshot effect decrease with the spatial expansion of the dopant, causing a dependence of the dopants’ ignition capability on the dopant mass. Here, we develop criteria (impact count functions) to assess the ignition capability of dopants, based on (i) the spatial overlap of the seed electron cloud with the He atoms and (ii) the overlap of their kinetic energy distribution with the distribution of Coulomb barrier heights at He. The relatively long time delays between the instants of dopant ionization and ignition (incubation times) for calcium doped droplets are determined to a large extent by the time it takes to deshield the dopant ions.

Delay-Dependent Exponential Stability for Discrete-Time BAM Neural Networks with Time-Varying Delays

Directory of Open Access Journals (Sweden)

Yonggang Chen

2008-01-01

Full Text Available This paper considers the delay-dependent exponential stability for discrete-time BAM neural networks with time-varying delays. By constructing the new Lyapunov functional, the improved delay-dependent exponential stability criterion is derived in terms of linear matrix inequality (LMI. Moreover, in order to reduce the conservativeness, some slack matrices are introduced in this paper. Two numerical examples are presented to show the effectiveness and less conservativeness of the proposed method.

Leveraging delay discounting for health: Can time delays influence food choice?

Science.gov (United States)

Appelhans, Bradley M; French, Simone A; Olinger, Tamara; Bogucki, Michael; Janssen, Imke; Avery-Mamer, Elizabeth F; Powell, Lisa M

2018-03-15

Delay discounting, the tendency to choose smaller immediate rewards over larger delayed rewards, is theorized to promote consumption of immediately rewarding but unhealthy foods at the expense of long-term weight maintenance and nutritional health. An untested implication of delay discounting models of decision-making is that selectively delaying access to less healthy foods may promote selection of healthier (immediately available) alternatives, even if they may be less desirable. The current study tested this hypothesis by measuring healthy versus regular vending machine snack purchasing before and during the implementation of a 25-s time delay on the delivery of regular snacks. Purchasing was also examined under a $0.25 discount on healthy snacks, a $0.25 tax on regular snacks, and the combination of both pricing interventions with the 25-s time delay. Across 32,019 vending sales from three separate vending locations, the 25-s time delay increased healthy snack purchasing from 40.1% to 42.5%, which was comparable to the impact of a $0.25 discount (43.0%). Combining the delay and the discount had a roughly additive effect (46.0%). However, the strongest effects were seen under the $0.25 tax on regular snacks (53.7%) and the combination of the delay and the tax (50.2%). Intervention effects varied substantially between vending locations. Importantly, time delays did not harm overall vending sales or revenue, which is relevant to the real-world feasibility of this intervention. More investigation is needed to better understand how the impact of time delays on food choice varies across populations, evaluate the effects of time delays on beverage vending choices, and extend this approach to food choices in contexts other than vending machines. ClinicalTrials.gov, NCT02359916. Copyright © 2018 Elsevier Ltd. All rights reserved.

Dynamics of Nonlinear Time-Delay Systems

CERN Document Server

Lakshmanan, Muthusamy

2010-01-01

Synchronization of chaotic systems, a patently nonlinear phenomenon, has emerged as a highly active interdisciplinary research topic at the interface of physics, biology, applied mathematics and engineering sciences. In this connection, time-delay systems described by delay differential equations have developed as particularly suitable tools for modeling specific dynamical systems. Indeed, time-delay is ubiquitous in many physical systems, for example due to finite switching speeds of amplifiers in electronic circuits, finite lengths of vehicles in traffic flows, finite signal propagation times in biological networks and circuits, and quite generally whenever memory effects are relevant. This monograph presents the basics of chaotic time-delay systems and their synchronization with an emphasis on the effects of time-delay feedback which give rise to new collective dynamics. Special attention is devoted to scalar chaotic/hyperchaotic time-delay systems, and some higher order models, occurring in different bran...

Standardized Gasoline Compression Ignition Fuels Matrix

KAUST Repository

Badra, Jihad; Bakor, Radwan; AlRamadan, Abdullah; Almansour, Mohammed; Sim, Jaeheon; Ahmed, Ahfaz; Viollet, Yoann; Chang, Junseok

2018-01-01

Direct injection compression ignition engines running on gasoline-like fuels have been considered an attractive alternative to traditional spark ignition and diesel engines. The compression and lean combustion mode eliminates throttle losses yielding higher thermodynamic efficiencies and the better mixing of fuel/air due to the longer ignition delay times of the gasoline-like fuels allows better emission performance such as nitric oxides (NOx) and particulate matter (PM). These gasoline-like fuels which usually have lower octane compared to market gasoline have been identified as a viable option for the gasoline compression ignition (GCI) engine applications due to its lower reactivity and lighter evaporation compared to diesel. The properties, specifications and sources of these GCI fuels are not fully understood yet because this technology is relatively new. In this work, a GCI fuel matrix is being developed based on the significance of certain physical and chemical properties in GCI engine operation. Those properties were chosen to be density, temperature at 90 volume % evaporation (T90) or final boiling point (FBP) and research octane number (RON) and the ranges of these properties were determined from the data reported in literature. These proposed fuels were theoretically formulated, while applying realistic constraints, using species present in real refinery streams. Finally, three-dimensional (3D) engine computational fluid dynamics (CFD) simulations were performed using the proposed GCI fuels and the similarities and differences were highlighted.

Standardized Gasoline Compression Ignition Fuels Matrix

KAUST Repository

Badra, Jihad

2018-04-03

Direct injection compression ignition engines running on gasoline-like fuels have been considered an attractive alternative to traditional spark ignition and diesel engines. The compression and lean combustion mode eliminates throttle losses yielding higher thermodynamic efficiencies and the better mixing of fuel/air due to the longer ignition delay times of the gasoline-like fuels allows better emission performance such as nitric oxides (NOx) and particulate matter (PM). These gasoline-like fuels which usually have lower octane compared to market gasoline have been identified as a viable option for the gasoline compression ignition (GCI) engine applications due to its lower reactivity and lighter evaporation compared to diesel. The properties, specifications and sources of these GCI fuels are not fully understood yet because this technology is relatively new. In this work, a GCI fuel matrix is being developed based on the significance of certain physical and chemical properties in GCI engine operation. Those properties were chosen to be density, temperature at 90 volume % evaporation (T90) or final boiling point (FBP) and research octane number (RON) and the ranges of these properties were determined from the data reported in literature. These proposed fuels were theoretically formulated, while applying realistic constraints, using species present in real refinery streams. Finally, three-dimensional (3D) engine computational fluid dynamics (CFD) simulations were performed using the proposed GCI fuels and the similarities and differences were highlighted.

Ignition studies of n-heptane/iso-octane/toluene blends

KAUST Repository

Javed, Tamour

2016-07-09

Ignition delay times of four ternary blends of n-heptane/iso-octane/toluene, referred to as Toluene Primary Reference Fuels (TPRFs), have been measured in a high-pressure shock tube and in a rapid compression machine. The TPRFs were formulated to match the research octane number (RON) and motor octane number (MON) of two high-octane gasolines and two prospective low-octane naphtha fuels. The experiments were carried out over a wide range of temperatures (650–1250 K), at pressures of 10, 20 and 40 bar, and at equivalence ratios of 0.5 and 1.0. It was observed that the ignition delay times of these TPRFs exhibit negligible octane dependence at high temperatures (T > 1000 K), weak octane dependence at low temperatures (T < 700 K), and strong octane dependence in the negative temperature coefficient (NTC) regime. A detailed chemical kinetic model was used to simulate and interpret the measured data. It was shown that the kinetic model requires general improvements to better predict low-temperature conditions and particularly requires improvements for high sensitivity (high toluene concentration) TPRF blends. These datasets will serve as important benchmark for future gasoline surrogate mechanism development and validation. © 2016 The Combustion Institute

Study of ignition characteristics of microemulsion of coconut oil under off diesel engine conditions

Directory of Open Access Journals (Sweden)

Mahir H. Salmani

2015-09-01

Full Text Available The increasing awareness of the depletion of fossil fuel resources and the environmental benefits motivates the use of vegetable oils, however there is little known information about ignition and combustion characteristics of vegetable oil based fuels under off diesel engine conditions. These conditions are normally reached either during starting or when the engine is sufficiently worn out. A fuel was prepared by co-solvent blending of coconut oil with 20% butyl alcohol and was analysed. An experimental study of the measurement of ignition delay (ID characteristics of conical fuel sprays impinging on hot surface in cylindrical combustion chamber was carried out. The objective of the study was to investigate the effect of hot surface temperatures on ignition delays of microemulsion of coconut oil at various ambient air pressures and temperatures which would have reached under off diesel engine conditions. An experimental set-up was designed and developed for a maximum air pressure of 200 bar and a maximum temperature of 800 °C with the emphasis on optical method for the measurement of ignition delay. Hot surface temperature range chosen was 300–450 °C and ambient air pressure (inside the combustion chamber range chosen was 10–25 bar. Present study shows that at fixed injection pressure and fixed ambient (hot surface temperature, at higher ambient air pressure (25 bar inside the combustion chamber, ignition delay of diesel and microemulsion of coconut oil are comparable and therefore are having matching combustion characteristics. Although a pressure of 25 bar is much less than the precombustion pressure of most diesel engines but again conclusively establish that combustion characteristics are same despite lower air pressure, temperature and lower injection pressure. At higher injection pressure ignition delay of microemulsion of coconut oil and pure diesel attains the lower value at the same ambient air pressure inside the

High temperature shock tube experiments and kinetic modeling study of diisopropyl ketone ignition and pyrolysis

KAUST Repository

Barari, Ghazal; Pryor, Owen; Koroglu, Batikan; Sarathy, Mani; Masunov, Artë m E.; Vasu, Subith S.

2017-01-01

Diisopropyl ketone (DIPK) is a promising biofuel candidate, which is produced using endophytic fungal conversion. In this work, a high temperature detailed combustion kinetic model for DIPK was developed using the reaction class approach. DIPK ignition and pyrolysis experiments were performed using the UCF shock tube. The shock tube oxidation experiments were conducted between 1093K and 1630K for different reactant compositions, equivalence ratios (φ=0.5–2.0), and pressures (1–6atm). In addition, methane concentration time-histories were measured during 2% DIPK pyrolysis in argon using cw laser absorption near 3400nm at temperatures between 1300 and 1400K near 1atm. To the best of our knowledge, current ignition delay times (above 1050K) and methane time histories are the first such experiments performed in DIPK at high temperatures. Present data were used as validation targets for the new kinetic model and simulation results showed fair agreement compared to the experiments. The reaction rates corresponding to the main consumption pathways of DIPK were found to have high sensitivity in controlling the reactivity, so these were adjusted to attain better agreement between the simulation and experimental data. A correlation was developed based on the experimental data to predict the ignition delay times using the temperature, pressure, fuel concentration and oxygen concentration.

High temperature shock tube experiments and kinetic modeling study of diisopropyl ketone ignition and pyrolysis

KAUST Repository

Barari, Ghazal

2017-03-10

Diisopropyl ketone (DIPK) is a promising biofuel candidate, which is produced using endophytic fungal conversion. In this work, a high temperature detailed combustion kinetic model for DIPK was developed using the reaction class approach. DIPK ignition and pyrolysis experiments were performed using the UCF shock tube. The shock tube oxidation experiments were conducted between 1093K and 1630K for different reactant compositions, equivalence ratios (φ=0.5–2.0), and pressures (1–6atm). In addition, methane concentration time-histories were measured during 2% DIPK pyrolysis in argon using cw laser absorption near 3400nm at temperatures between 1300 and 1400K near 1atm. To the best of our knowledge, current ignition delay times (above 1050K) and methane time histories are the first such experiments performed in DIPK at high temperatures. Present data were used as validation targets for the new kinetic model and simulation results showed fair agreement compared to the experiments. The reaction rates corresponding to the main consumption pathways of DIPK were found to have high sensitivity in controlling the reactivity, so these were adjusted to attain better agreement between the simulation and experimental data. A correlation was developed based on the experimental data to predict the ignition delay times using the temperature, pressure, fuel concentration and oxygen concentration.

Automobile Engine: Basic Ignition Timing. Fordson Bilingual Demonstration Project.

Science.gov (United States)

Vick, James E.

These two vocational instructional modules on basic automobile ignition timing and on engine operation, four-stroke cycle, are two of eight such modules designed to assist recently arrived Arab students, limited in English proficiency (LEP), in critical instructional areas in a comprehensive high school. Goal stated for this module is for the…

Time-resolved measurements of the hot-electron population in ignition-scale experiments on the National Ignition Facility (invited)

Energy Technology Data Exchange (ETDEWEB)

Hohenberger, M., E-mail: mhoh@lle.rochester.edu; Stoeckl, C. [Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States); Albert, F.; Palmer, N. E.; Döppner, T.; Divol, L.; Dewald, E. L.; Bachmann, B.; MacPhee, A. G.; LaCaille, G.; Bradley, D. K. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Lee, J. J. [National Security Technologies LLC, Livermore, California 94551 (United States)

2014-11-15

In laser-driven inertial confinement fusion, hot electrons can preheat the fuel and prevent fusion-pellet compression to ignition conditions. Measuring the hot-electron population is key to designing an optimized ignition platform. The hot electrons in these high-intensity, laser-driven experiments, created via laser-plasma interactions, can be inferred from the bremsstrahlung generated by hot electrons interacting with the target. At the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)], the filter-fluorescer x-ray (FFLEX) diagnostic–a multichannel, hard x-ray spectrometer operating in the 20–500 keV range–has been upgraded to provide fully time-resolved, absolute measurements of the bremsstrahlung spectrum with ∼300 ps resolution. Initial time-resolved data exhibited significant background and low signal-to-noise ratio, leading to a redesign of the FFLEX housing and enhanced shielding around the detector. The FFLEX x-ray sensitivity was characterized with an absolutely calibrated, energy-dispersive high-purity germanium detector using the high-energy x-ray source at NSTec Livermore Operations over a range of K-shell fluorescence energies up to 111 keV (U K{sub β}). The detectors impulse response function was measured in situ on NIF short-pulse (∼90 ps) experiments, and in off-line tests.

Progress Toward Ignition on the National Ignition Facility

International Nuclear Information System (INIS)

Kauffman, R.L.

2011-01-01

The principal approach to ignition on the National Ignition Facility (NIF) is indirect drive. A schematic of an ignition target is shown in Figure 1. The laser beams are focused through laser entrance holes at each end of a high-Z cylindrical case, or hohlraum. The lasers irradiate the hohlraum walls producing x-rays that ablate and compress the fuel capsule in the center of the hohlraum. The hohlraum is made of Au, U, or other high-Z material. For ignition targets, the hohlraum is ∼0.5 cm diameter by ∼1 cm in length. The hohlraum absorbs the incident laser energy producing x-rays for symmetrically imploding the capsule. The fuel capsule is a ∼2-mm-diameter spherical shell of CH, Be, or C filled with DT fuel. The DT fuel is in the form of a cryogenic layer on the inside of the capsule. X-rays ablate the outside of the capsule, producing a spherical implosion. The imploding shell stagnates in the center, igniting the DT fuel. NIC has overseen installation of all of the hardware for performing ignition experiments, including commissioning of approximately 50 diagnostic systems in NIF. The diagnostics measure scattered optical light, x-rays from the hohlraum over the energy range from 100 eV to 500 keV, and x-rays, neutrons, and charged particles from the implosion. An example of a diagnostic is the Magnetic Recoil Spectrometer (MRS) built by a collaboration of scientists from MIT, UR-LLE, and LLNL shown in Figure 2. MRS measures the neutron spectrum from the implosion, providing information on the neutron yield and areal density that are metrics of the quality of the implosion. Experiments on NIF extend ICF research to unexplored regimes in target physics. NIF can produce more than 50 times the laser energy and more than 20 times the power of any previous ICF facility. Ignition scale hohlraum targets are three to four times larger than targets used at smaller facilities, and the ignition drive pulses are two to five times longer. The larger targets and longer

Optimization of the National Ignition Facility primary shield design

International Nuclear Information System (INIS)

Annese, C.E.; Watkins, E.F.; Greenspan, E.; Miller, W.F.

1993-10-01

Minimum cost design concepts of the primary shield for the National Ignition laser fusion experimental Facility (NIF) are searched with the help of the optimization code SWAN. The computational method developed for this search involves incorporating the time dependence of the delayed photon field within effective delayed photon production cross sections. This method enables one to address the time-dependent problem using relatively simple, time-independent transport calculations, thus significantly simplifying the design process. A novel approach was used for the identification of the optimal combination of constituents that will minimize the shield cost; it involves the generation, with SWAN, of effectiveness functions for replacing materials on an equal cost basis. The minimum cost shield design concept was found to consist of a mixture of polyethylene and low cost, low activation materials such as SiC, with boron added near the shield boundaries

Synchronization of delayed systems in the presence of delay time modulation

International Nuclear Information System (INIS)

Kye, Won-Ho; Choi, Muhan; Kim, Myung-Woon; Lee, Soo-Young; Rim, Sunghwan; Kim, Chil-Min; Park, Young-Jai

2004-01-01

We investigate synchronization in the presence of delay time modulation for application to communication. We have observed that the robust synchronization is established by a common delay signal and its threshold is presented using Lyapunov exponents analysis. The influence of the delay time modulation in chaotic oscillators is also discussed

Combustion characteristics of compressed natural gas/diesel dual-fuel turbocharged compressed ignition engine

Energy Technology Data Exchange (ETDEWEB)

Shenghua, L.; Longbao, Z.; Ziyan, W.; Jiang, R. [Xi' an Jiaotong Univ. (China). Dept. of Automotive Engineering

2003-09-01

The combustion characteristics of a turbocharged natural gas and diesel dual-fuelled compression ignition (CI) engine are investigated. With the measured cylinder pressures of the engine operated on pure diesel and dual fuel, the ignition delay, effects of pilot diesel and engine load on combustion characteristics are analysed. Emissions of HC, CO, NO{sub x} and smoke are measured and studied too. The results show that the quantity of pilot diesel has important effects on the performance and emissions of a dual-fuel engine at low-load operating conditions. Ignition delay varies with the concentration of natural gas. Smoke is much lower for the developed dual-fuel engine under all the operating conditions. (Author)

Ignition dynamics and activation energies of metallic thermites: From nano- to micron-scale particulate composites

Science.gov (United States)

Hunt, Emily M.; Pantoya, Michelle L.

2005-08-01

Ignition behaviors associated with nano- and micron-scale particulate composite thermites were studied experimentally and modeled theoretically. The experimental analysis utilized a CO2 laser ignition apparatus to ignite the front surface of compacted nickel (Ni) and aluminum (Al) pellets at varying heating rates. Ignition delay time and ignition temperature as a function of both Ni and Al particle size were measured using high-speed imaging and microthermocouples. The apparent activation energy was determined from this data using a Kissinger isoconversion method. This study shows that the activation energy is significantly lower for nano- compared with micron-scale particulate media (i.e., as low as 17.4 compared with 162.5kJ /mol, respectively). Two separate Arrhenius-type mathematical models were developed that describe ignition in the nano- and the micron-composite thermites. The micron-composite model is based on a heat balance while the nanocomposite model incorporates the energy of phase transformation in the alumina shell theorized to be an initiating step in the solid-solid diffusion reaction and uniquely appreciable in nanoparticle media. These models were found to describe the ignition of the Ni /Al alloy for a wide range of heating rates.

Periodic flows to chaos in time-delay systems

CERN Document Server

Luo, Albert C J

2017-01-01

This book for the first time examines periodic motions to chaos in time-delay systems, which exist extensively in engineering. For a long time, the stability of time-delay systems at equilibrium has been of great interest from the Lyapunov theory-based methods, where one cannot achieve the ideal results. Thus, time-delay discretization in time-delay systems was used for the stability of these systems. In this volume, Dr. Luo presents an accurate method based on the finite Fourier series to determine periodic motions in nonlinear time-delay systems. The stability and bifurcation of periodic motions are determined by the time-delayed system of coefficients in the Fourier series and the method for nonlinear time-delay systems is equivalent to the Laplace transformation method for linear time-delay systems. Facilitates discovery of analytical solutions of nonlinear time-delay systems; Illustrates bifurcation trees of periodic motions to chaos; Helps readers identify motion complexity and singularity; Explains pro...

Time-Delay System Identification Using Genetic Algorithm

DEFF Research Database (Denmark)

Yang, Zhenyu; Seested, Glen Thane

2013-01-01

Due to the unknown dead-time coefficient, the time-delay system identification turns to be a non-convex optimization problem. This paper investigates the identification of a simple time-delay system, named First-Order-Plus-Dead-Time (FOPDT), by using the Genetic Algorithm (GA) technique. The qual......Due to the unknown dead-time coefficient, the time-delay system identification turns to be a non-convex optimization problem. This paper investigates the identification of a simple time-delay system, named First-Order-Plus-Dead-Time (FOPDT), by using the Genetic Algorithm (GA) technique...

Effect of glycerol ethoxylate as an ignition improver on injection and combustion characteristics of hydrous ethanol under CI engine condition

International Nuclear Information System (INIS)

Munsin, R.; Laoonual, Y.; Jugjai, S.; Matsuki, M.; Kosaka, H.

2015-01-01

Highlights: • Glycerol ethoxylate (GE) shows the similar results as the commercial additive. • GE decreases injection rate, but increases injection delay and duration of ethanol. • GE shortens ignition delay and decreases heat released in premixed burn of ethanol. • GE has a minor effect on flame temperature of ethanol. • KL factor and soot of ethanol are sensitive to both GE and the commercial additive. - Abstract: This paper investigates the effects of glycerol ethoxylate as an ignition improver on injection and combustion characteristics of hydrous ethanol under a CI engine condition. Injection characteristics were investigated by an in-house injection rate measurement device based on the Zeuch method, while spray combustion has been performed in the rapid compression and expansion machine (RCEM). The CI engine condition indicated as density, pressure and temperature of compressed synthetic gas, consisting of 80% argon and 20% oxygen, at fuel injection timing in RCEM of 21 kg/m 3 , 4.4 MPa and 900 K, respectively. This condition is equivalent to the isentropic compression of air of the actual CI engine with compression ratio of 22. Hydrous ethanol without ignition improver (Eh95) and the ethanol dedicated for heavy duty vehicles (ED95: composed of hydrous ethanol with the commercial additive for ED95) are reference fuels representing low and high quality ethanol fuel for CI engines, respectively. All test fuels are injected at constant heat input. The results indicate that the additional ignition improvers change injection characteristics, i.e. injection delay, injection rate and discharge coefficient of hydrous ethanol. The maximum injection rates at fully opened needle for the ethanol dedicated for heavy duty vehicles (ED95) and hydrous ethanol with 5% glycerol ethoxylate (5%GE) are lower than that of hydrous ethanol without ignition improver (Eh95) by approximately 10%. Additional injection duration is required for ED95 and 5%GE to maintain a

Effects of ignition parameters on combustion process of a rotary engine fueled with natural gas

International Nuclear Information System (INIS)

Fan, Baowei; Pan, Jianfeng; Liu, Yangxian; Zhu, Yuejin

2015-01-01

Highlights: • A 3-D simulation model based on the chemical reaction kinetics is established. • The tumble near the trailing spark plug is beneficial for the combustion rate. • The best position of the trailing spark plug is at the rear of the tumble zone. • An increase of the tumble effect time can improve the combustion rate. • Considering the rate of pressure rise, the best ignition timing is 50 °CA (BTDC). - Abstract: The side-ported rotary engine fueled with natural gas is a new, clean, efficient energy system. This work aims to numerically study the performance, combustion and emission characteristics of a side-ported rotary engine fueled with natural gas under different ignition positions and ignition timings. Simulations were performed using multi-dimensional software ANASYS Fluent. On the basis of the software, a three-dimensional dynamic simulation model was established by writing dynamic mesh programs and choosing a detailed reaction mechanism. The three-dimensional dynamic simulation model, based on the chemical reaction kinetics, was also validated by the experimental data. Meanwhile, further simulations were then conducted to investigate how to impact the combustion process by the coupling function between ignition operating parameter and the flow field inside the cylinder. Simulation results showed that in order to improve the combustion efficiency, the trailing spark plug should be located at the rear of the tumble zone and the ignition timing should be advanced properly. This was mainly caused by the trailing spark plug being located at the rear of the tumble zone, as it not only allowed the fuel in the rear of combustion chamber to be burnt without delay, but also permitted the acceleration of the flame propagation by the tumble. Meanwhile, with advanced ignition timing, the time between ignition timing and the timing of the tumble disappearance increased, which led to an increase of the tumble effect time used to improve the combustion

Antiknock quality and ignition kinetics of 2-phenylethanol, a novel lignocellulosic octane booster

KAUST Repository

Shankar, Vijai

2016-06-28

High-octane quality fuels are important for increasing spark ignition engine efficiency, but their production comes at a substantial economic and environmental cost. The possibility of producing high anti-knock quality gasoline by blending high-octane bio-derived components with low octane naphtha streams is attractive. 2-phenyl ethanol (2-PE), is one such potential candidate that can be derived from lignin, a biomass component made of interconnected aromatic groups. We first ascertained the blending anti-knock quality of 2-PE by studying the effect of spark advancement on knock for various blends 2-PE, toluene, and ethanol with naphtha in a cooperative fuels research engine. The blending octane quality of 2-PE indicated an anti-knock behavior similar or slightly greater than that of toluene, and ethylbenzene, which could be attributed to either chemical kinetics or charge cooling effects. To isolate chemical kinetic effects, a model for 2-PE auto-ignition was developed and validated using ignition delay times measured in a high-pressure shock tube. Simulated ignition delay times of 2-PE were also compared to those of traditional high-octane gasoline blending components to show that the gas phase reactivity of 2-PE is lower than ethanol, and comparable to toluene, and ethylbenzene at RON, and MON relevant conditions. The gas-phase reactivity of 2-PE is largely controlled by its aromatic ring, while the effect of the hydroxyl group is minimal. The higher blending octane quality of 2-PE compared to toluene, and ethylbenzene can be attributed primarily to the effect of the hydroxyl group on increasing heat of vaporization. © 2016 The Combustion Institute.

Combustion Characteristics of C5 Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

KAUST Repository

Park, Sungwoo; Chung, Suk-Ho; Lu, Tianfeng; Sarathy, Mani

2015-01-01

) and their mixtures with primary reference fuels (PRFs) were studied using a detailed chemical kinetic model obtained from merging previously published mechanisms. Ignition delay times of the C5 alcohol/air mixtures were compared to PRFs at 20 and 40 atm. Reaction

Ignition of a lean PRF/air mixture under RCCI/SCCI conditions: Chemical aspects

KAUST Repository

Luong, Minh Bau

2016-10-10

Chemical aspects of the ignition of a primary reference fuel (PRF)/air mixture under reactivity controlled compression ignition (RCCI) and stratified charge compression ignition (SCCI) conditions are investigated by analyzing two-dimensional direct numerical simulation (DNS) data with chemical explosive mode (CEM) analysis. CEMA is adopted to provide fundamental insights into the ignition process by identifying controlling species and elementary reactions at different locations and times. It is found that at the first ignition delay, low-temperature chemistry (LTC) represented by the isomerization of alkylperoxy radical, chain branching reactions of keto-hydroperoxide, and H-atom abstraction of n-heptane is predominant for both RCCI and SCCI combustion. In addition, explosion index and participation index analyses together with conditional means on temperature verify that low-temperature heat release (LTHR) from local mixtures with relatively-high n-heptane concentration occurs more intensively in RCCI combustion than in SCCI combustion, which ultimately advances the overall RCCI combustion and distributes its heat release rate over time. It is also found that at the onset of the main combustion, high-temperature heat release (HTHR) occurs primarily in thin deflagrations where temperature, CO, and OH are found to be the most important species for the combustion. The conversion reaction of CO to CO and hydrogen chemistry are identified as important reactions for HTHR. The overall RCCI/SCCI combustion can be understood by mapping the variation of 2-D RCCI/SCCI combustion in temperature space onto the temporal evolution of 0-D ignition.

CFD modeling of two-stage ignition in a rapid compression machine: Assessment of zero-dimensional approach

Energy Technology Data Exchange (ETDEWEB)

Mittal, Gaurav [Department of Mechanical Engineering, The University of Akron, Akron, OH 44325 (United States); Raju, Mandhapati P. [General Motor R and D Tech Center, Warren, MI 48090 (United States); Sung, Chih-Jen [Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269 (United States)

2010-07-15

In modeling rapid compression machine (RCM) experiments, zero-dimensional approach is commonly used along with an associated heat loss model. The adequacy of such approach has not been validated for hydrocarbon fuels. The existence of multi-dimensional effects inside an RCM due to the boundary layer, roll-up vortex, non-uniform heat release, and piston crevice could result in deviation from the zero-dimensional assumption, particularly for hydrocarbons exhibiting two-stage ignition and strong thermokinetic interactions. The objective of this investigation is to assess the adequacy of zero-dimensional approach in modeling RCM experiments under conditions of two-stage ignition and negative temperature coefficient (NTC) response. Computational fluid dynamics simulations are conducted for n-heptane ignition in an RCM and the validity of zero-dimensional approach is assessed through comparisons over the entire NTC region. Results show that the zero-dimensional model based on the approach of 'adiabatic volume expansion' performs very well in adequately predicting the first-stage ignition delays, although quantitative discrepancy for the prediction of the total ignition delays and pressure rise in the first-stage ignition is noted even when the roll-up vortex is suppressed and a well-defined homogeneous core is retained within an RCM. Furthermore, the discrepancy is pressure dependent and decreases as compressed pressure is increased. Also, as ignition response becomes single-stage at higher compressed temperatures, discrepancy from the zero-dimensional simulations reduces. Despite of some quantitative discrepancy, the zero-dimensional modeling approach is deemed satisfactory from the viewpoint of the ignition delay simulation. (author)

Effects of computing time delay on real-time control systems

Science.gov (United States)

Shin, Kang G.; Cui, Xianzhong

1988-01-01

The reliability of a real-time digital control system depends not only on the reliability of the hardware and software used, but also on the speed in executing control algorithms. The latter is due to the negative effects of computing time delay on control system performance. For a given sampling interval, the effects of computing time delay are classified into the delay problem and the loss problem. Analysis of these two problems is presented as a means of evaluating real-time control systems. As an example, both the self-tuning predicted (STP) control and Proportional-Integral-Derivative (PID) control are applied to the problem of tracking robot trajectories, and their respective effects of computing time delay on control performance are comparatively evaluated. For this example, the STP (PID) controller is shown to outperform the PID (STP) controller in coping with the delay (loss) problem.

Ignition modes of nanosecond discharge with bubbles in distilled water

International Nuclear Information System (INIS)

Hamdan, Ahmad; Cha, Min Suk

2015-01-01

Here, we present the microscopic physical characteristics of nanosecond discharges with an array of bubbles in distilled water. In particular, applying a single high-voltage pulse, four delayed intensified charge-coupled device cameras successfully visualized four successive images during a single discharge event. We identified three distinctive modes of ignition inside a bubble, depending on the relative location of the bubble with respect to pin-to-hollow needle electrodes when a single bubble was located in an inter-electrode gap of 1 mm: anode-driven ignition, cathode-driven ignition, and co-ignition near both electrodes. Anode- and cathode-driven ignitions evolved into either a complete propagation of the streamer or an incomplete propagation, which were limited in location by proximity to an ignition location, while co-ignitions consistently showed complete propagation. When we increased the gap to 2 mm to accommodate multiple bubbles in the gap, an ignited bubble near the cathode was able to cause the ignition of an upper adjacent bubble. Bubble–bubble interface zones can also be spots of ignition, such that we observed simultaneous co-ignitions in the zones of bubble–bubble interfaces and near electrodes with triple bubbles. We compared the experimental results of discharge propagation with different ignition modes between Ar, He, and N 2 bubbles. In addition, numerical simulations for static electric fields reasonably supported observed ignition behavior such that field intensity was locally enhanced. (paper)

Numerical research of heat and mass transfer at the ignition of system “fabric – combustible liquid – oxidant” by the local energy source

Directory of Open Access Journals (Sweden)

Glushkov Dmitrii O.

2015-01-01

Full Text Available A numerical research was executed for macroscopic regularities determination of heat and mass transfer processes under the conditions of phase transformation and chemical reaction at the ignition of vapour coming from fabrics impregnated by typical combustible liquid into oxidant area at the local power supply. Limit conditions of heterogeneous system “fabric – combustible liquid – oxidant” ignition at the heating of single metal particle was established. Dependences of ignition delay time on temperature and rates of local power source were obtained.

Synchronization of Markovian jumping stochastic complex networks with distributed time delays and probabilistic interval discrete time-varying delays

International Nuclear Information System (INIS)

Li Hongjie; Yue Dong

2010-01-01

The paper investigates the synchronization stability problem for a class of complex dynamical networks with Markovian jumping parameters and mixed time delays. The complex networks consist of m modes and the networks switch from one mode to another according to a Markovian chain with known transition probability. The mixed time delays are composed of discrete and distributed delays, the discrete time delay is assumed to be random and its probability distribution is known a priori. In terms of the probability distribution of the delays, the new type of system model with probability-distribution-dependent parameter matrices is proposed. Based on the stochastic analysis techniques and the properties of the Kronecker product, delay-dependent synchronization stability criteria in the mean square are derived in the form of linear matrix inequalities which can be readily solved by using the LMI toolbox in MATLAB, the solvability of derived conditions depends on not only the size of the delay, but also the probability of the delay-taking values in some intervals. Finally, a numerical example is given to illustrate the feasibility and effectiveness of the proposed method.

Compositional effects on the ignition of FACE gasolines

KAUST Repository

Sarathy, Mani; Kukkadapu, Goutham; Mehl, Marco; Javed, Tamour; Ahmed, Ahfaz; Naser, Nimal; Tekawade, Aniket; Kosiba, Graham; Alabbad, Mohammed; Singh, Eshan; Park, Sungwoo; Rashidi, Mariam Al; Chung, Suk-Ho; Roberts, William L.; Oehlschlaeger, Matthew A.; Sung, Chih-Jen; Farooq, Aamir

2016-01-01

As regulatory measures for improved fuel economy and decreased emissions are pushing gasoline engine combustion technologies towards extreme conditions (i.e., boosted and intercooled intake with exhaust gas recirculation), fuel ignition characteristics become increasingly important for enabling stable operation. This study explores the effects of chemical composition on the fundamental ignition behavior of gasoline fuels. Two well-characterized, high-octane, non-oxygenated FACE (Fuels for Advanced Combustion Engines) gasolines, FACE F and FACE G, having similar antiknock indices but different octane sensitivities and chemical compositions are studied. Ignition experiments were conducted in shock tubes and a rapid compression machine (RCM) at nominal pressures of 20 and 40. atm, equivalence ratios of 0.5 and 1.0, and temperatures ranging from 650 to 1270. K. Results at temperatures above 900. K indicate that ignition delay time is similar for these fuels. However, RCM measurements below 900. K demonstrate a stronger negative temperature coefficient behavior for FACE F gasoline having lower octane sensitivity. In addition, RCM pressure profiles under two-stage ignition conditions illustrate that the magnitude of low-temperature heat release (LTHR) increases with decreasing fuel octane sensitivity. However, intermediate-temperature heat release is shown to increase as fuel octane sensitivity increases. Various surrogate fuel mixtures were formulated to conduct chemical kinetic modeling, and complex multicomponent surrogate mixtures were shown to reproduce experimentally observed trends better than simpler two- and three-component mixtures composed of n-heptane, iso-octane, and toluene. Measurements in a Cooperative Fuels Research (CFR) engine demonstrated that the multicomponent surrogates accurately captured the antiknock quality of the FACE gasolines. Simulations were performed using multicomponent surrogates for FACE F and G to reveal the underlying chemical

Compositional effects on the ignition of FACE gasolines

KAUST Repository

Sarathy, Mani

2016-05-08

As regulatory measures for improved fuel economy and decreased emissions are pushing gasoline engine combustion technologies towards extreme conditions (i.e., boosted and intercooled intake with exhaust gas recirculation), fuel ignition characteristics become increasingly important for enabling stable operation. This study explores the effects of chemical composition on the fundamental ignition behavior of gasoline fuels. Two well-characterized, high-octane, non-oxygenated FACE (Fuels for Advanced Combustion Engines) gasolines, FACE F and FACE G, having similar antiknock indices but different octane sensitivities and chemical compositions are studied. Ignition experiments were conducted in shock tubes and a rapid compression machine (RCM) at nominal pressures of 20 and 40. atm, equivalence ratios of 0.5 and 1.0, and temperatures ranging from 650 to 1270. K. Results at temperatures above 900. K indicate that ignition delay time is similar for these fuels. However, RCM measurements below 900. K demonstrate a stronger negative temperature coefficient behavior for FACE F gasoline having lower octane sensitivity. In addition, RCM pressure profiles under two-stage ignition conditions illustrate that the magnitude of low-temperature heat release (LTHR) increases with decreasing fuel octane sensitivity. However, intermediate-temperature heat release is shown to increase as fuel octane sensitivity increases. Various surrogate fuel mixtures were formulated to conduct chemical kinetic modeling, and complex multicomponent surrogate mixtures were shown to reproduce experimentally observed trends better than simpler two- and three-component mixtures composed of n-heptane, iso-octane, and toluene. Measurements in a Cooperative Fuels Research (CFR) engine demonstrated that the multicomponent surrogates accurately captured the antiknock quality of the FACE gasolines. Simulations were performed using multicomponent surrogates for FACE F and G to reveal the underlying chemical

Time-delayed chameleon: Analysis, synchronization and FPGA implementation

Science.gov (United States)

Rajagopal, Karthikeyan; Jafari, Sajad; Laarem, Guessas

2017-12-01

In this paper we report a time-delayed chameleon-like chaotic system which can belong to different families of chaotic attractors depending on the choices of parameters. Such a characteristic of self-excited and hidden chaotic flows in a simple 3D system with time delay has not been reported earlier. Dynamic analysis of the proposed time-delayed systems are analysed in time-delay space and parameter space. A novel adaptive modified functional projective lag synchronization algorithm is derived for synchronizing identical time-delayed chameleon systems with uncertain parameters. The proposed time-delayed systems and the synchronization algorithm with controllers and parameter estimates are then implemented in FPGA using hardware-software co-simulation and the results are presented.

Time Delay Estimation Algoritms for Echo Cancellation

Directory of Open Access Journals (Sweden)

Kirill Sakhnov

2011-01-01

Full Text Available The following case study describes how to eliminate echo in a VoIP network using delay estimation algorithms. It is known that echo with long transmission delays becomes more noticeable to users. Thus, time delay estimation, as a part of echo cancellation, is an important topic during transmission of voice signals over packetswitching telecommunication systems. An echo delay problem associated with IP-based transport networks is discussed in the following text. The paper introduces the comparative study of time delay estimation algorithm, used for estimation of the true time delay between two speech signals. Experimental results of MATLab simulations that describe the performance of several methods based on cross-correlation, normalized crosscorrelation and generalized cross-correlation are also presented in the paper.

Modelling piloted ignition of wood and plastics

International Nuclear Information System (INIS)

Blijderveen, Maarten van; Bramer, Eddy A.; Brem, Gerrit

2012-01-01

Highlights: ► We model piloted ignition times of wood and plastics. ► The model is applied on a packed bed. ► When the air flow is above a critical level, no ignition can take place. - Abstract: To gain insight in the startup of an incinerator, this article deals with piloted ignition. A newly developed model is described to predict the piloted ignition times of wood, PMMA and PVC. The model is based on the lower flammability limit and the adiabatic flame temperature at this limit. The incoming radiative heat flux, sample thickness and moisture content are some of the used variables. Not only the ignition time can be calculated with the model, but also the mass flux and surface temperature at ignition. The ignition times for softwoods and PMMA are mainly under-predicted. For hardwoods and PVC the predicted ignition times agree well with experimental results. Due to a significant scatter in the experimental data the mass flux and surface temperature calculated with the model are hard to validate. The model is applied on the startup of a municipal waste incineration plant. For this process a maximum allowable primary air flow is derived. When the primary air flow is above this maximum air flow, no ignition can be obtained.

Influence of Polymer-Clay Interfacial Interactions on the Ignition Time of Polymer/Clay Nanocomposites.

Science.gov (United States)

Zope, Indraneel S; Dasari, Aravind; Yu, Zhong-Zhen

2017-08-11

Metal ions present on smectite clay (montmorillonite) platelets have preferential reactivity towards peroxy/alkoxy groups during polyamide 6 (PA6) thermal decomposition. This changes the decomposition pathway and negatively affects the ignition response of PA6. To restrict these interfacial interactions, high-temperature-resistant polymers such as polyetherimide (PEI) and polyimide (PI) were used to coat clay layers. PEI was deposited on clay by solution-precipitation, whereas PI was deposited through a solution-imidization-precipitation technique before melt blending with PA6. The absence of polymer-clay interfacial interactions has resulted in a similar time-to-ignition of PA6/PEI-clay (133 s) and PA6/PI-clay (139 s) composites as neat PA6 (140 s). On the contrary, PA6 with conventional ammonium-based surfactant modified clay has showed a huge drop in time-to-ignition (81 s), as expected. The experimental evidences provided herein reveal the role of the catalytic activity of clay during the early stages of polymer decomposition.

Time-Delay Effects on Constitutive Gene Expression*

International Nuclear Information System (INIS)

Feng Yan-Ling; Wang Dan; Tang Xu-Lei; Dong Jian-Min

2017-01-01

The dynamics of constitutive gene expression with delayed mRNA degradation is investigated, where the intrinsic noise caused by the small number of reactant molecules is introduced. It is found that the oscillatory behavior claimed in previous investigations does not appear in the approximation of small time delay, and the steady state distribution still follows the Poisson law. Furthermore, we introduce the extrinsic noise induced by surrounding environment to explore the effects of this noise and time delay on the Fano factor. Based on a delay Langevin equation and the corresponding Fokker–Planck equation, the distribution of mRNA copy-number is achieved analytically. The time delay and extrinsic noise play similar roles in the gene expression system, that is, they are able to result in the deviation of the Fano factor from 1 evidently. The measured Fano factor for constitutive gene expression is slightly larger than 1, which is perhaps attributed to the time-delay effect. (paper)

Thermal re-ignition processes of switching arcs with various gas-blast using voltage application highly controlled by powersemiconductors

Science.gov (United States)

Nakano, Tomoyuki; Tanaka, Yasunori; Murai, K.; Uesugi, Y.; Ishijima, T.; Tomita, K.; Suzuki, K.; Shinkai, T.

2018-05-01

This paper focuses on a fundamental experimental approach to thermal arc re-ignition processes in a variety of gas flows in a nozzle. Using power semiconductor switches in the experimental system, the arc current and the voltage applied to the arc were controlled with precise timing. With this system, residual arcs were created in decaying phase under free recovery conditions; arc re-ignition was then intentionally instigated by application of artificial voltage—i.e. quasi-transient recovery voltage—to study the arc behaviour in both decaying and re-ignition phases. In this study, SF6, CO2, N2, O2, air and Ar arcs were intentionally re-ignited by quasi-TRV application at 20 μs delay time from initiation of free recovery condition. Through these experiments, the electron density at the nozzle throat was measured using a laser Thomson scattering method together with high speed video camera observation during the re-ignition process. Temporal variations in the electron density from the arc decaying to re-ignition phases were successfully obtained for each gas-blast arc at the nozzle throat. In addition, initial dielectric recovery properties of SF6, CO2, air and Ar arcs were measured under the same conditions. These data will be useful in the fundamental elucidation of thermal arc re-ignition processes.

AN EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF VARIABLE VALVE TIMING ON THE PERFORMANCE IN SPARK IGNITION ENGINE

Directory of Open Access Journals (Sweden)

Ali AKBAŞ

2001-01-01

Full Text Available In this study, an alternative prototype has been designed and constructed for variable valve timing systems which are used in spark ignition engines. The effects of intake valve timing and lift changing on engine performance have been investigated without changing the opening duration of the valves. A four stroke, single cylinder, spark ignition engine has been used for these experiments.

Ignition parameters and early flame kernel development of laser-ignited combustible gas mixtures

International Nuclear Information System (INIS)

Kopecek, H.; Wintner, E.; Ruedisser, D.; Iskra, K.; Neger, T.

2002-01-01

Full text: Laser induced breakdown of focused pulsed laser radiation, the subsequent plasma formation and thermalization offers a possibility of ignition of combustible gas mixtures free from electrode interferences, an arbitrary choice of the location within the medium and exact timing regardless of the degree of turbulence. The development and the decreasing costs of solid state laser technologies approach the pay-off for the higher complexity of such an ignition system due to several features unique to laser ignition. The feasability of laser ignition was demonstrated in an 1.5 MW(?) natural gas engine, and several investigations were performed to determine optimal ignition energies, focus shapes and laser wavelengths. The early flame kernel development was investigated by time resolved planar laser induced fluorescence of the OH-radical which occurs predominantly in the flame front. The flame front propagation showed typical features like toroidal initial flame development, flame front return and highly increased flame speed along the laser focus axis. (author)

Long-time behavior for suspension bridge equations with time delay

Science.gov (United States)

Park, Sun-Hye

2018-04-01

In this paper, we consider suspension bridge equations with time delay of the form u_{tt}(x,t) + Δ ^2 u (x,t) + k u^+ (x,t) + a_0 u_t (x,t) + a_1 u_t (x, t- τ ) + f(u(x,t)) = g(x). Many researchers have studied well-posedness, decay rates of energy, and existence of attractors for suspension bridge equations without delay effects. But, as far as we know, there is no work about suspension equations with time delay. In addition, there are not many studies on attractors for other delayed systems. Thus we first provide well-posedness for suspension equations with time delay. And then show the existence of global attractors and the finite dimensionality of the attractors by establishing energy functionals which are related to the norm of the phase space to our problem.

Reconstruction of ensembles of coupled time-delay systems from time series.

Science.gov (United States)

Sysoev, I V; Prokhorov, M D; Ponomarenko, V I; Bezruchko, B P

2014-06-01

We propose a method to recover from time series the parameters of coupled time-delay systems and the architecture of couplings between them. The method is based on a reconstruction of model delay-differential equations and estimation of statistical significance of couplings. It can be applied to networks composed of nonidentical nodes with an arbitrary number of unidirectional and bidirectional couplings. We test our method on chaotic and periodic time series produced by model equations of ensembles of diffusively coupled time-delay systems in the presence of noise, and apply it to experimental time series obtained from electronic oscillators with delayed feedback coupled by resistors.

Delay time and tunneling transient phenomena

International Nuclear Information System (INIS)

Garcia-Calderon, Gaston; Villavicencio, Jorge

2002-01-01

Analytic solutions to the time-dependent Schroedinger equation for cutoff wave initial conditions are used to investigate the time evolution of the transmitted probability density for tunneling. For a broad range of values of the potential barrier opacity α, we find that the probability density exhibits two evolving structures. One refers to the propagation of a forerunner related to a time domain resonance [Phys. Rev. A 64, 0121907 (2001)], while the other consists of a semiclassical propagating wave front. We find a regime where the forerunners are absent, corresponding to positive time delays, and show that this regime is characterized by opacities α c . The critical opacity α c is derived from the analytical expression for the delay time, which reflects a link between transient effects in tunneling and the delay time

Time delayed Ensemble Nudging Method

Science.gov (United States)

An, Zhe; Abarbanel, Henry

Optimal nudging method based on time delayed embedding theory has shows potentials on analyzing and data assimilation in previous literatures. To extend the application and promote the practical implementation, new nudging assimilation method based on the time delayed embedding space is presented and the connection with other standard assimilation methods are studied. Results shows the incorporating information from the time series of data can reduce the sufficient observation needed to preserve the quality of numerical prediction, making it a potential alternative in the field of data assimilation of large geophysical models.

Influence of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition

Directory of Open Access Journals (Sweden)

Guo Zerong

2016-01-01

Full Text Available To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.

Progress in the shock-ignition inertial confinement fusion concept

International Nuclear Information System (INIS)

Theobald, W.; Casner, A.; Nora, R.; Ribeyre, X.; Lafon, M.; Anderson, K. S.; Betti, R.; Craxton, R. S.; Delettrez, J. A.; Frenje, J. A.; Glebov, V. Yu; Gotchev, O. V.; Hohenberger, M.; Hu, S. X.; Marshall, F. J.; McCrory, R. L.; Meyerhofer, D. D.; Perkins, L. J.; Sangster, T. C.; Schurtz, G.; Seka, W.; Smalyuk, V. A.; Stoeckl, C.; Yaakobi, B.

2013-01-01

Shock-ignition experiments with peak laser intensities of ∼8 x 10 15 W/cm 2 were performed. D 2 -filled plastic shells were compressed on a low adiabat by 40 of the 60 OMEGA beams. The remaining 20 beams were delayed and tightly focused onto the imploding shell to generate a strong shock. Up to 35% backscattering of laser energy was measured at the highest intensity. Hard x-ray measurements reveal a relatively low hot-electron temperature of ∼40 keV, independent of intensity and spike onset time. (authors)

Progress Toward Analytic Predictions of Supersonic Hydrocarbon-Air Combustion: Computation of Ignition Times and Supersonic Mixing Layers

Science.gov (United States)

Sexton, Scott Michael

Combustion in scramjet engines is faced with the limitation of brief residence time in the combustion chamber, requiring fuel and preheated air streams to mix and ignite in a matter of milliseconds. Accurate predictions of autoignition times are needed to design reliable supersonic combustion chambers. Most efforts in estimating non-premixed autoignition times have been devoted to hydrogen-air mixtures. The present work addresses hydrocarbon-air combustion, which is of interest for future scramjet engines. Computation of ignition in supersonic flows requires adequate characterization of ignition chemistry and description of the flow, both of which are derived in this work. In particular, we have shown that activation energy asymptotics combined with a previously derived reduced chemical kinetic mechanism provides analytic predictions of autoignition times in homogeneous systems. Results are compared with data from shock tube experiments, and previous expressions which employ a fuel depletion criterion. Ignition in scramjet engines has a strong dependence on temperature, which is found by perturbing the chemically frozen mixing layer solution. The frozen solution is obtained here, accounting for effects of viscous dissipation between the fuel and air streams. We investigate variations of thermodynamic and transport properties, and compare these to simplified mixing layers which neglect these variations. Numerically integrating the mixing layer problem reveals a nonmonotonic temperature profile, with a peak occurring inside the shear layer for sufficiently high Mach numbers. These results will be essential in computation of ignition distances in supersonic combustion chambers.

Improved Criteria on Delay-Dependent Stability for Discrete-Time Neural Networks with Interval Time-Varying Delays

Directory of Open Access Journals (Sweden)

O. M. Kwon

2012-01-01

Full Text Available The purpose of this paper is to investigate the delay-dependent stability analysis for discrete-time neural networks with interval time-varying delays. Based on Lyapunov method, improved delay-dependent criteria for the stability of the networks are derived in terms of linear matrix inequalities (LMIs by constructing a suitable Lyapunov-Krasovskii functional and utilizing reciprocally convex approach. Also, a new activation condition which has not been considered in the literature is proposed and utilized for derivation of stability criteria. Two numerical examples are given to illustrate the effectiveness of the proposed method.

Ignition probabilities for Compact Ignition Tokamak designs

International Nuclear Information System (INIS)

Stotler, D.P.; Goldston, R.J.

1989-09-01

A global power balance code employing Monte Carlo techniques had been developed to study the ''probability of ignition'' and has been applied to several different configurations of the Compact Ignition Tokamak (CIT). Probability distributions for the critical physics parameters in the code were estimated using existing experimental data. This included a statistical evaluation of the uncertainty in extrapolating the energy confinement time. A substantial probability of ignition is predicted for CIT if peaked density profiles can be achieved or if one of the two higher plasma current configurations is employed. In other cases, values of the energy multiplication factor Q of order 10 are generally obtained. The Ignitor-U and ARIES designs are also examined briefly. Comparisons of our empirically based confinement assumptions with two theory-based transport models yield conflicting results. 41 refs., 11 figs

Ignition et oxydation des particules de combustible solide pulvérisé Ignition and Oxidation of Pulverized Solid Fuel

Directory of Open Access Journals (Sweden)

De Soete G. G.

2006-11-01

the rate of heterogeneous combustion can reach its normal steady state, which is practically the same as that of char. At temperatures between the ignition temperature of the solid fuel and the extinction temperature of residual char, combustion is incomplete and extinction occurs at a devolatilization degree that is all the greater as the temperature is high. This phenomenon can be qualitively explained by the standard thermal ignition theory when it is applied to the specific case of pyrolyzable solid fuels. Ignition temperatures as well as ignition delays have been determined for a great many lower- and higher-rank solid fuels (coals, cokes, asphaltenes, soot, wood, graphite. An analysis of the experimental rate of heterogeneous combustion, and especially of the apparent activation temperature, and its dependency with regard to particle size and oxygen concentration, shows that this combustion is controlled under test conditions by CO desorption and that it occurs mainly in the mixed kinetico-diffusional regime. Investigations of the dependency of ignition delays with regard to temperature, to particle size and to oxygen partial pressure suggest that reactions occur in a pure kinetic regime during such delays and that the desorption reaction product is mainly CO.

Time domain passivity controller for 4-channel time-delay bilateral teleoperation.

Science.gov (United States)

Rebelo, Joao; Schiele, Andre

2015-01-01

This paper presents an extension of the time-domain passivity control approach to a four-channel bilateral controller under the effects of time delays. Time-domain passivity control has been used successfully to stabilize teleoperation systems with position-force and position-position controllers; however, the performance with such control architectures is sub-optimal both with and without time delays. This work extends the network representation of the time-domain passivity controller to the four-channel architecture, which provides perfect transparency to the user without time delay. The proposed architecture is based on modelling the controllers as dependent voltage sources and using only series passivity controllers. The obtained results are shown on a one degree-of-freedom setup and illustrate the stabilization behaviour of the proposed controller when time delay is present in the communication channel.

Combustion Characteristics of C5 Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

KAUST Repository

Park, Sungwoo

2015-10-27

C5 alcohols are considered alternative fuels because they emit less greenhouse gases and fewer harmful pollutants. In this study, the combustion characteristics of 2-methylbutanol (2-methyl-1-butanol) and isopentanol (3-methyl-1-butanol) and their mixtures with primary reference fuels (PRFs) were studied using a detailed chemical kinetic model obtained from merging previously published mechanisms. Ignition delay times of the C5 alcohol/air mixtures were compared to PRFs at 20 and 40 atm. Reaction path analyses were conducted at intermediate and high temperatures to identify the most influential reactions controlling ignition of C5 alcohols. The direct relation graph with expert knowledge methodology was used to eliminate unimportant species and reactions in the detailed mechanism, and the resulting skeletal mechanism was tested at various homogeneous charge compression ignition (HCCI) engine combustion conditions. These simulations were used to investigate the heat release characteristics of the methyl-substituted C5 alcohols, and the results show relatively strong reactions at intermediate temperatures prior to hot ignition. C5 alcohol blending in PRF75 in HCCI combustion leads to a significant decrease of low-temperature heat release (LTHR) and a delay of the main combustion. The heat release features demonstrated by C5 alcohols can be used to improve the design and operation of advanced engine technologies.

An experimental and numerical analysis of the HCCI auto-ignition process of primary reference fuels, toluene reference fuels and diesel fuel in an engine, varying the engine parameters

Energy Technology Data Exchange (ETDEWEB)

Machrafi, Hatim; Cavadias, Simeon [UPMC Universite Paris 06, LGPPTS, Ecole Nationale Superieure de Chimie de Paris, 11, rue de Pierre et Marie Curie, 75005 Paris (France); UPMC Universite Paris 06, Institut Jean Le Rond D' Alembert, 2, place de la Gare de Ceinture, 78210 St Cyr-I' Ecole (France); Gilbert, Philippe [UPMC Universite Paris 06, Institut Jean Le Rond D' Alembert, 2, place de la Gare de Ceinture, 78210 St Cyr-I' Ecole (France)

2008-11-15

For a future HCCI engine to operate under conditions that adhere to environmental restrictions, reducing fuel consumption and maintaining or increasing at the same time the engine efficiency, the choice of the fuel is crucial. For this purpose, this paper presents an auto-ignition investigation concerning the primary reference fuels, toluene reference fuels and diesel fuel, in order to study the effect of linear alkanes, branched alkanes and aromatics on the auto-ignition. The auto-ignition of these fuels has been studied at inlet temperatures from 25 to 120 C, at equivalence ratios from 0.18 to 0.53 and at compression ratios from 6 to 13.5, in order to extend the range of investigation and to assess the usability of these parameters to control the auto-ignition. It appeared that both iso-octane and toluene delayed the ignition with respect to n-heptane, while toluene has the strongest effect. This means that aromatics have higher inhibiting effects than branched alkanes. In an increasing order, the inlet temperature, equivalence ratio and compression ratio had a promoting effect on the ignition delays. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process. (author)

Effect of Temperature, Pressure and Equivalence Ratio on Ignition Delay in Ignition Quality Tester (IQT): Diesel,n-Heptane, andiso-Octane Fuels under Low Temperature Conditions

KAUST Repository

Yang, Seung Yeon; Naser, Nimal; Chung, Suk-Ho; Cha, Junepyo

2015-01-01

-octane in relatively low temperature conditions to simulate unsteady spray ignition behavior. A KAUST Research ignition quality tester (KR-IQT) was utilized, which has a feature of varying temperature, pressure and equivalence ratio using a variable displacement fuel

Electrically tunable photonic true-time-delay line.

Science.gov (United States)

Barmenkov, Yuri O; Cruz, José Luis; Díez, Antonio; Andrés, Miguel V

2010-08-16

We present a new application of the acousto-optic superlattice modulation of a fiber Bragg grating based on the dynamic phase and group delay properties of this fiber-optic component. We demonstrate a tunable photonic true-time-delay line based on the group delay change of the light reflected from the grating sidebands. The delay is electrically tuned by adjusting the voltage applied to a piezoelectric transducer that generates the acoustic wave propagating along the grating. In our experiments, a true-time delay of 400 ps is continuously adjusted (300 ps within the 3 dB amplitude range of the first sideband), using a 12 cm long uniform grating.

Shock timing on the National Ignition Facility: The first precision tuning series

Directory of Open Access Journals (Sweden)

Robey H.F.

2013-11-01

Full Text Available Ignition implosions on the National Ignition Facility (NIF [Lindl et al., Phys. Plasmas 11, 339 (2004] are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision in order to keep the fuel on a low adiabat. The first series of precision tuning experiments on NIF have been performed. These experiments use optical diagnostics to directly measure the strength and timing of all four shocks inside the hohlraum-driven, cryogenic deuterium-filled capsule interior. The results of these experiments are presented demonstrating a significant decrease in the fuel adiabat over previously un-tuned implosions. The impact of the improved adiabat on fuel compression is confirmed in related deuterium-tritium (DT layered capsule implosions by measurement of fuel areal density (ρR, which show the highest fuel compression (ρR ∼ 1.0 g/cm2 measured to date.

Moments of the Wigner delay times

International Nuclear Information System (INIS)

Berkolaiko, Gregory; Kuipers, Jack

2010-01-01

The Wigner time delay is a measure of the time spent by a particle inside the scattering region of an open system. For chaotic systems, the statistics of the individual delay times (whose average is the Wigner time delay) are thought to be well described by random matrix theory. Here we present a semiclassical derivation showing the validity of random matrix results. In order to simplify the semiclassical treatment, we express the moments of the delay times in terms of correlation functions of scattering matrices at different energies. In the semiclassical approximation, the elements of the scattering matrix are given in terms of the classical scattering trajectories, requiring one to study correlations between sets of such trajectories. We describe the structure of correlated sets of trajectories and formulate the rules for their evaluation to the leading order in inverse channel number. This allows us to derive a polynomial equation satisfied by the generating function of the moments. Along with showing the agreement of our semiclassical results with the moments predicted by random matrix theory, we infer that the scattering matrix is unitary to all orders in the semiclassical approximation.

Studies into laser ignition of confined pyrotechnics

Energy Technology Data Exchange (ETDEWEB)

Ahmad, S.R.; Russell, D.A. [Centre for Applied Laser Spectroscopy, DASSR, Defence Academy, Cranfield University, Shrivenham, Swindon (United Kingdom)

2008-10-15

Ignition tests were carried out on three different pyrotechnics using laser energy from the multimode output from an Ar-Ion laser (av) at 500 nm and a near-IR diode laser pigtailed to a fibre optic cable and operating at 808 nm. The pyrotechnics investigated were: G20 black powder, SR44 and SR371C. The confined ignition tests were conducted in a specially designed ignition chamber. Pyrotechnics were ignited by a free space beam entering the chamber through an industrial sapphire window in the case of the Ar-ion laser. For the NIR diode laser, fibre was ducted through a block into direct contact with the pyrotechnic. The Ar-Ion laser was chosen as this was found to ignite all three pyrotechnics in the unconfined condition. It also allowed for a direct comparison of confined/unconfined results to be made. The threshold laser flux densities to initiate reproducible ignitions at this wavelength were found to be between {proportional_to}12.7 and {proportional_to}0.16 kW cm{sup -2}. Plotted on the ignition maps are the laser flux densities versus the start of ignition times for the three confined pyrotechnics. It was found from these maps that the times for confined ignition were substantially lower than those obtained for unconfined ignition under similar experimental conditions. For the NIR diode laser flux densities varied between {proportional_to}6.8 and {proportional_to}0.2 kW cm{sup -2}. The minimum ignition times for the NIR diode laser for SR371C ({proportional_to}11.2 ms) and G20 ({proportional_to}17.1 ms) were faster than those achieved by the use of the Ar-ion laser. However, the minimum ignition time was shorter ({proportional_to}11.7 ms) with the Ar-ion laser for SR44. (Abstract Copyright [2008], Wiley Periodicals, Inc.)

Time-Delay Interferometry

Directory of Open Access Journals (Sweden)

Massimo Tinto

2014-08-01

Full Text Available Equal-arm detectors of gravitational radiation allow phase measurements many orders of magnitude below the intrinsic phase stability of the laser injecting light into their arms. This is because the noise in the laser light is common to both arms, experiencing exactly the same delay, and thus cancels when it is differenced at the photo detector. In this situation, much lower level secondary noises then set the overall performance. If, however, the two arms have different lengths (as will necessarily be the case with space-borne interferometers, the laser noise experiences different delays in the two arms and will hence not directly cancel at the detector. In order to solve this problem, a technique involving heterodyne interferometry with unequal arm lengths and independent phase-difference readouts has been proposed. It relies on properly time-shifting and linearly combining independent Doppler measurements, and for this reason it has been called time-delay interferometry (TDI. This article provides an overview of the theory, mathematical foundations, and experimental aspects associated with the implementation of TDI. Although emphasis on the application of TDI to the Laser Interferometer Space Antenna (LISA mission appears throughout this article, TDI can be incorporated into the design of any future space-based mission aiming to search for gravitational waves via interferometric measurements. We have purposely left out all theoretical aspects that data analysts will need to account for when analyzing the TDI data combinations.

Photothermally activated motion and ignition using aluminum nanoparticles

International Nuclear Information System (INIS)

Abboud, Jacques E.; Chong Xinyuan; Zhang Mingjun; Zhang Zhili; Jiang Naibo; Roy, Sukesh; Gord, James R.

2013-01-01

The aluminum nanoparticles (Al NPs) are demonstrated to serve as active photothermal media, to enhance and control local photothermal energy deposition via the photothermal effect activated by localized surface plasmon resonance (LSPR) and amplified by Al NPs oxidation. The activation source is a 2-AA-battery-powered xenon flash lamp. The extent of the photothermally activated movement of Al NPs can be ∼6 mm. Ignition delay can be ∼0.1 ms. Both scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements of motion-only and after-ignition products confirm significant Al oxidation occurs through sintering and bursting after the flash exposure. Simulations suggest local heat generation is enhanced by LSPR. The positive-feedback effects from the local heat generation amplified by Al oxidation produce a large increase in local temperature and pressure, which enhances movement and accelerates ignition.

Global chaos synchronization with channel time-delay

International Nuclear Information System (INIS)

Jiang Guoping; Zheng Weixing; Chen Guanrong

2004-01-01

This paper addresses a practical issue in chaos synchronization where there is a time-delay in the receiver as compared with the transmitter. A new synchronization scheme and a general criterion for global chaos synchronization are proposed and developed from the approach of unidirectional linear error feedback coupling with time-delay. The chaotic Chua's circuit is used for illustration, where the coupling parameters are determined according to the criterion under which the global chaos synchronization of the time-delay coupled systems is achieved

Time-delayed feedback control of diffusion in random walkers

Science.gov (United States)

Ando, Hiroyasu; Takehara, Kohta; Kobayashi, Miki U.

2017-07-01

Time delay in general leads to instability in some systems, while specific feedback with delay can control fluctuated motion in nonlinear deterministic systems to a stable state. In this paper, we consider a stochastic process, i.e., a random walk, and observe its diffusion phenomenon with time-delayed feedback. As a result, the diffusion coefficient decreases with increasing delay time. We analytically illustrate this suppression of diffusion by using stochastic delay differential equations and justify the feasibility of this suppression by applying time-delayed feedback to a molecular dynamics model.

Ignition experiment - alternatives

International Nuclear Information System (INIS)

Knobloch, A.F.

1979-10-01

This report comprises three short papers on cost estimates, integral burn time and alternative versions of Tokamak ignition experiments. These papers were discussed at the ZEPHYR workshop with participants from IPP Garching, MIT Cambridge and PPPL Princeton (Garching July 30 - August 2 1979) (Chapters A, B, C). It is shown, that starting from a practical parameter independent minimum integral burn time of Tokamak ignition experiments (some 10 3 s) by adding a shield for protection of the magnet insulation (permitted neutron dose 10 9 rad) an integral burn time of some 10 4 s can be achieved for only about 30% more outlay. For a substantially longer integral burn time the outlay approaches rather quickly that for a Tokamak reactor. Some examples for alternatives to ZEPHYR are being given, including some with low or no compression. In a further chapter D some early results of evaluating an ignition experiment on the basis of the energy confinement scaling put forward by Coppi and Mazzucato are presented. As opposed to the case of the Alcator scaling used in chapters A through C the minimum integral burn time of Tokamak ignition experiments here depends on the plasma current. Provided neutral injectors up to about 160 keV are available compression boosting is not required with this scaling. The results presented have been obtained neglecting the effects of the toroidal field ripple. (orig.) 891 HT/orig. 892 RKD [de

Generalized Synchronization of Time-Delayed Discrete Systems

International Nuclear Information System (INIS)

Jing Jianyi; Min Lequan

2009-01-01

This paper establishes two theorems for two time-delayed (chaotic) discrete systems to achieve time-delayed generalized synchronization (TDGS). These two theorems uncover the general forms of two TDGS systems via a prescribed transformation. As examples, we convert the Lorenz three-dimensional chaotic map to an equal time-delayed system as the driving system, and construct the TDGS driven systems according to the Theorems 1 and 2. Numerical simulations demonstrate the effectiveness of the proposed theorems. (interdisciplinary physics and related areas of science and technology)

Time delay interferometry with moving spacecraft arrays

International Nuclear Information System (INIS)

Tinto, Massimo; Estabrook, F.B.; Armstrong, J.W.

2004-01-01

Space-borne interferometric gravitational wave detectors, sensitive in the low-frequency (millihertz) band, will fly in the next decade. In these detectors the spacecraft-to-spacecraft light-travel-times will necessarily be unequal, time varying, and (due to aberration) have different time delays on up and down links. The reduction of data from moving interferometric laser arrays in solar orbit will in fact encounter nonsymmetric up- and down-link light time differences that are about 100 times larger than has previously been recognized. The time-delay interferometry (TDI) technique uses knowledge of these delays to cancel the otherwise dominant laser phase noise and yields a variety of data combinations sensitive to gravitational waves. Under the assumption that the (different) up- and down-link time delays are constant, we derive the TDI expressions for those combinations that rely only on four interspacecraft phase measurements. We then turn to the general problem that encompasses time dependence of the light-travel times along the laser links. By introducing a set of noncommuting time-delay operators, we show that there exists a quite general procedure for deriving generalized TDI combinations that account for the effects of time dependence of the arms. By applying our approach we are able to re-derive the 'flex-free' expression for the unequal-arm Michelson combinations X 1 , and obtain the generalized expressions for the TDI combinations called relay, beacon, monitor, and symmetric Sagnac

The effects of the framing of time on delay discounting.

Science.gov (United States)

DeHart, William Brady; Odum, Amy L

2015-01-01

We examined the effects of the framing of time on delay discounting. Delay discounting is the process by which delayed outcomes are devalued as a function of time. Time in a titrating delay discounting task is often framed in calendar units (e.g., as 1 week, 1 month, etc.). When time is framed as a specific date, delayed outcomes are discounted less compared to the calendar format. Other forms of framing time; however, have not been explored. All participants completed a titrating calendar unit delay-discounting task for money. Participants were also assigned to one of two delay discounting tasks: time as dates (e.g., June 1st, 2015) or time in units of days (e.g., 5000 days), using the same delay distribution as the calendar delay-discounting task. Time framed as dates resulted in less discounting compared to the calendar method, whereas time framed as days resulted in greater discounting compared to the calendar method. The hyperboloid model fit best compared to the hyperbola and exponential models. How time is framed may alter how participants attend to the delays as well as how the delayed outcome is valued. Altering how time is framed may serve to improve adherence to goals with delayed outcomes. © Society for the Experimental Analysis of Behavior.

Time delay in a multichannel formalism

International Nuclear Information System (INIS)

Haberzettl, Helmut; Workman, Ron

2007-01-01

We reexamine the time-delay formalism of Wigner, Eisenbud, and Smith, which was developed to analyze both elastic and inelastic resonances. An error in the paper of Smith has propagated through the literature. We correct this error and show how the results of Eisenbud and Smith are related. We also comment on some recent time-delay studies, based on Smith's erroneous interpretation of the Eisenbud result

Time delays, population, and economic development

Science.gov (United States)

Gori, Luca; Guerrini, Luca; Sodini, Mauro

2018-05-01

This research develops an augmented Solow model with population dynamics and time delays. The model produces either a single stationary state or multiple stationary states (able to characterise different development regimes). The existence of time delays may cause persistent fluctuations in both economic and demographic variables. In addition, the work identifies in a simple way the reasons why economics affects demographics and vice versa.

Gravitational Lens Time Delays Using Polarization Monitoring

Directory of Open Access Journals (Sweden)

Andrew Biggs

2017-11-01

Full Text Available Gravitational lens time delays provide a means of measuring the expansion of the Universe at high redshift (and therefore in the ‘Hubble flow’ that is independent of local calibrations. It was hoped that many of the radio lenses found in the JVAS/CLASS survey would yield time delays as these were selected to have flat spectra and are dominated by multiple compact components. However, despite extensive monitoring with the Very Large Array (VLA, time delays have only been measured for three of these systems (out of 22. We have begun a programme to reanalyse the existing VLA monitoring data with the goal of producing light curves in polarized flux and polarization position angle, either to improve delay measurements or to find delays for new sources. Here, we present preliminary results on the lens system B1600+434 which demonstrate the presence of correlated and substantial polarization variability in each image.

Fusion ignition via a magnetically-assisted fast ignition approach

OpenAIRE

Wang, W. -M.; Gibbon, P.; Sheng, Z. -M.; Li, Y. T.; Zhang, J.

2016-01-01

Significant progress has been made towards laser-driven fusion ignition via different schemes, including direct and indirect central ignition, fast ignition, shock ignition, and impact ignition schemes. However, to reach ignition conditions, there are still various technical and physical challenges to be solved for all these schemes. Here, our multi-dimensional integrated simulation shows that the fast-ignition conditions could be achieved when two 2.8 petawatt heating laser pulses counter-pr...

Delay-dependent exponential stability of cellular neural networks with time-varying delays

International Nuclear Information System (INIS)

Zhang Qiang; Wei Xiaopeng; Xu Jin

2005-01-01

The global exponential stability of cellular neural networks (CNNs) with time-varying delays is analyzed. Two new sufficient conditions ensuring global exponential stability for delayed CNNs are obtained. The conditions presented here are related to the size of delay. The stability results improve the earlier publications. Two examples are given to demonstrate the effectiveness of the obtained results

Influence of Absorption of Thermal Radiation in the Surface Water Film on the Characteristics and Ignition Conditions

Directory of Open Access Journals (Sweden)

Syrodoy Samen V.

2016-01-01

Full Text Available The results of the mathematical modeling of homogeneous particle ignition process of coal-water fuel covered with water film have been presented in article. The set co-occurring physical (inert heating, evaporation of water film and thermochemical (thermal degradation, inflammation process have been considered. Heat inside the film has been considered as the model of radiation-conductive heat transfer. Delay times have been determined according to the results of numerical modeling of the ignition. It has been shown that the water film can have a significant impact on performance and the ignition conditions. It has been found that heating main fuel layer occurs in the process of evaporation of water film. For this reason, the next (after the evaporation of the water film thermal preparation (coal heating, thermal decomposition of the organic part of the fuel and inflammation occur faster.

Delay-Dependent Guaranteed Cost Control of an Interval System with Interval Time-Varying Delay

Directory of Open Access Journals (Sweden)

Xiao Min

2009-01-01

Full Text Available This paper concerns the problem of the delay-dependent robust stability and guaranteed cost control for an interval system with time-varying delay. The interval system with matrix factorization is provided and leads to less conservative conclusions than solving a square root. The time-varying delay is assumed to belong to an interval and the derivative of the interval time-varying delay is not a restriction, which allows a fast time-varying delay; also its applicability is broad. Based on the Lyapunov-Ktasovskii approach, a delay-dependent criterion for the existence of a state feedback controller, which guarantees the closed-loop system stability, the upper bound of cost function, and disturbance attenuation lever for all admissible uncertainties as well as out perturbation, is proposed in terms of linear matrix inequalities (LMIs. The criterion is derived by free weighting matrices that can reduce the conservatism. The effectiveness has been verified in a number example and the compute results are presented to validate the proposed design method.

Discrete-time BAM neural networks with variable delays

Science.gov (United States)

Liu, Xin-Ge; Tang, Mei-Lan; Martin, Ralph; Liu, Xin-Bi

2007-07-01

This Letter deals with the global exponential stability of discrete-time bidirectional associative memory (BAM) neural networks with variable delays. Using a Lyapunov functional, and linear matrix inequality techniques (LMI), we derive a new delay-dependent exponential stability criterion for BAM neural networks with variable delays. As this criterion has no extra constraints on the variable delay functions, it can be applied to quite general BAM neural networks with a broad range of time delay functions. It is also easy to use in practice. An example is provided to illustrate the theoretical development.

Discrete-time BAM neural networks with variable delays

International Nuclear Information System (INIS)

Liu Xinge; Tang Meilan; Martin, Ralph; Liu Xinbi

2007-01-01

This Letter deals with the global exponential stability of discrete-time bidirectional associative memory (BAM) neural networks with variable delays. Using a Lyapunov functional, and linear matrix inequality techniques (LMI), we derive a new delay-dependent exponential stability criterion for BAM neural networks with variable delays. As this criterion has no extra constraints on the variable delay functions, it can be applied to quite general BAM neural networks with a broad range of time delay functions. It is also easy to use in practice. An example is provided to illustrate the theoretical development

Time-delay analyzer with continuous discretization

International Nuclear Information System (INIS)

Bayatyan, G.L.; Darbinyan, K.T.; Mkrtchyan, K.K.; Stepanyan, S.S.

1988-01-01

A time-delay analyzer is described which when triggered by a start pulse of adjustable duration performs continuous discretization of the analyzed signal within nearly 22 ns time intervals, the recording in a memory unit with following slow read-out of the information to the computer and its processing. The time-delay analyzer consists of four CAMAC-VECTOR systems of unit width. With its help one can separate comparatively short, small-amplitude rare signals against the background of quasistationary noise processes. 4 refs.; 3 figs

The national ignition facility: path to ignition in the laboratory

International Nuclear Information System (INIS)

Moses, E.I.; Bonanno, R.E.; Haynam, C.A.; Kauffman, R.L.; MacGowan, B.J.; Patterson Jr, R.W.; Sawicki, R.H.; Van Wonterghem, B.M.

2007-01-01

The National Ignition Facility (NIF) is a 192-beam laser facility presently under construction at Lawrence Livermore National Laboratory. When completed, NIF will be a 1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion ignition of deuterium-tritium plasmas in ICF (Inertial Confinement Fusion) targets and to perform high energy density experiments in support of the U.S. nuclear weapons stockpile. The NIF facility will consist of 2 laser bays, 4 capacitor areas, 2 laser switchyards, the target area and the building core. The laser is configured in 4 clusters of 48 beams, 2 in each laser bay. Four of the NIF beams have been already commissioned to demonstrate laser performance and to commission the target area including target and beam alignment and laser timing. During this time, NIF has demonstrated on a single-beam basis that it will meet its performance goals and has demonstrated its precision and flexibility for pulse shaping, pointing, timing and beam conditioning. It also performed 4 important experiments for ICF and High Energy Density Science. Presently, the project is installing production hardware to complete the project in 2009 with the goal to begin ignition experiments in 2010. An integrated plan has been developed including the NIF operations, user equipment such as diagnostics and cryogenic target capability, and experiments and calculations to meet this goal. This talk will provide NIF status, the plan to complete NIF, and the path to ignition. (authors)

Effect of main injection timing for controlling the combustion phasing of a homogeneous charge compression ignition engine using a new dual injection strategy

International Nuclear Information System (INIS)

Das, Pranab; Subbarao, P.M.V.; Subrahmanyam, J.P.

2015-01-01

Highlights: • A new dual injection concept is developed by minimum geometry modification. • The occurrence of combustion parameters strongly depend on main injection timing. • At higher load, premixed equivalence ratio dominates over main injection timing. • Retarded of main injection timing tends to retard combustion phasing. • Slightly retarded main injection timing is recommended to avoid intense knocking. - Abstract: Homogeneous charge compression ignition combustion of diesel fuel is implemented using a novel dual injection strategy. A new experimental technique is developed to modify a single cylinder direct injection diesel engine to run on homogeneous combustion mode. Effect of main injection timing is investigated covering a range from 26 to 8 crank angle degrees before top dead center with an interval of 3°. Retarded main injection timing is identified as a control strategy for delaying combustion phasing and a means of controlled combustion phasing of direct injection homogeneous charge compression ignition combustion. Two load conditions were investigated and it was observed that at higher load, start of combustion depends more on fuel air equivalence ratio than main injection timing, whereas at low load, it significantly varies with varying main injection timing. Significant improvements in smoke and oxides of nitrogen emissions are observed when compared with the baseline conventional combustion. By studying different combustion parameters, it is observed that there is an improvement in performance and emissions with marginal loss in thermal efficiency when the main injection timing is 20° before top dead center. This is identified as the optimum main injection timing for such homogeneous combustion under the same operating condition

Time-delayed autosynchronous swarm control.

Science.gov (United States)

Biggs, James D; Bennet, Derek J; Dadzie, S Kokou

2012-01-01

In this paper a general Morse potential model of self-propelling particles is considered in the presence of a time-delayed term and a spring potential. It is shown that the emergent swarm behavior is dependent on the delay term and weights of the time-delayed function, which can be set to induce a stationary swarm, a rotating swarm with uniform translation, and a rotating swarm with a stationary center of mass. An analysis of the mean field equations shows that without a spring potential the motion of the center of mass is determined explicitly by a multivalued function. For a nonzero spring potential the swarm converges to a vortex formation about a stationary center of mass, except at discrete bifurcation points where the center of mass will periodically trace an ellipse. The analytical results defining the behavior of the center of mass are shown to correspond with the numerical swarm simulations.

Numerical simulation of a liquid droplet combustion experiment focusing on ignition process

International Nuclear Information System (INIS)

Yamaguchi, Akira; Tajima, Yuji

1999-11-01

SPHINCS (Sodium Fire phenomenology IN multi-Cell System) computer program has been developed for the safety analysis of sodium fire accident in a Fast Breeder Reactor. The program can deal with spray combustion and pool surface combustion. In this report the authors investigate a single droplet combustion phenomena focusing on an ignition process. The spray combustion model of SPHINCS is as follows. The liquid droplet-burning rate after ignition is based on the D-square law and a diffusion flame assumption. Before the droplet is ignited, the burning rate is evaluated by mass flux of oxidizer gases. Forced convection effect that skews the sphere shape of the flame zone surrounding a droplet is taken into consideration. It enhances the burning rate. The chemical equilibrium theory is used to determine the resultant fraction of reaction products of Na-O 2 -H 2 O system. It is noted that users have to give an ignition temperature based on empirical evidences. According to this model, it is obvious that a smaller liquid droplet with higher initial temperature tends to burn more easily. What is observed in a recent experiment is that the smallest liquid droplet (2mm diameter) did not ignited of itself and larger droplets (3.7mm and 4.5mm diameter) burnt at 300degC initial temperature. The current model for liquid droplet combustion cannot predict the experimental results. Therefore, in the present study, a surface reaction model has been developed to predict the ignition process. The model has been used to analyze a combustion experiment of a stationary liquid droplet. The authors investigate the validity of the physical modeling of the liquid droplet combustion and surface reaction. It has been found, as the results, that the model can predict the influence of the initial temperature on the temperature lower limit for spontaneous ignition and ignition delay time. Also investigated is the influence of the moisture on the ignition phenomena. From the present study, it has

Maximum likelihood window for time delay estimation

International Nuclear Information System (INIS)

Lee, Young Sup; Yoon, Dong Jin; Kim, Chi Yup

2004-01-01

Time delay estimation for the detection of leak location in underground pipelines is critically important. Because the exact leak location depends upon the precision of the time delay between sensor signals due to leak noise and the speed of elastic waves, the research on the estimation of time delay has been one of the key issues in leak lovating with the time arrival difference method. In this study, an optimal Maximum Likelihood window is considered to obtain a better estimation of the time delay. This method has been proved in experiments, which can provide much clearer and more precise peaks in cross-correlation functions of leak signals. The leak location error has been less than 1 % of the distance between sensors, for example the error was not greater than 3 m for 300 m long underground pipelines. Apart from the experiment, an intensive theoretical analysis in terms of signal processing has been described. The improved leak locating with the suggested method is due to the windowing effect in frequency domain, which offers a weighting in significant frequencies.

The Strong Lensing Time Delay Challenge (2014)

Science.gov (United States)

Liao, Kai; Dobler, G.; Fassnacht, C. D.; Treu, T.; Marshall, P. J.; Rumbaugh, N.; Linder, E.; Hojjati, A.

2014-01-01

Time delays between multiple images in strong lensing systems are a powerful probe of cosmology. At the moment the application of this technique is limited by the number of lensed quasars with measured time delays. However, the number of such systems is expected to increase dramatically in the next few years. Hundred such systems are expected within this decade, while the Large Synoptic Survey Telescope (LSST) is expected to deliver of order 1000 time delays in the 2020 decade. In order to exploit this bounty of lenses we needed to make sure the time delay determination algorithms have sufficiently high precision and accuracy. As a first step to test current algorithms and identify potential areas for improvement we have started a "Time Delay Challenge" (TDC). An "evil" team has created realistic simulated light curves, to be analyzed blindly by "good" teams. The challenge is open to all interested parties. The initial challenge consists of two steps (TDC0 and TDC1). TDC0 consists of a small number of datasets to be used as a training template. The non-mandatory deadline is December 1 2013. The "good" teams that complete TDC0 will be given access to TDC1. TDC1 consists of thousands of lightcurves, a number sufficient to test precision and accuracy at the subpercent level, necessary for time-delay cosmography. The deadline for responding to TDC1 is July 1 2014. Submissions will be analyzed and compared in terms of predefined metrics to establish the goodness-of-fit, efficiency, precision and accuracy of current algorithms. This poster describes the challenge in detail and gives instructions for participation.

Assessing the prospects for achieving double-shell ignition on the National Ignition Facility using vacuum hohlraums

International Nuclear Information System (INIS)

Amendt, Peter; Cerjan, C.; Hamza, A.; Hinkel, D. E.; Milovich, J. L.; Robey, H. F.

2007-01-01

The goal of demonstrating ignition on the National Ignition Facility [J. D. Lindl et al., Phys. Plasmas 11, 339 (2003)] has motivated a revisit of double-shell (DS) targets as a complementary path to the cryogenic baseline approach. Expected benefits of DS ignition targets include noncryogenic deuterium-tritium (DT) fuel preparation, minimal hohlraum-plasma-mediated laser backscatter, low threshold-ignition temperatures (≅4 keV) for relaxed hohlraum x-ray flux asymmetry tolerances, and minimal (two-) shock timing requirements. On the other hand, DS ignition presents several formidable challenges, encompassing room-temperature containment of high-pressure DT (≅790 atm) in the inner shell, strict concentricity requirements on the two shells ( 2 nanoporous aerogels with suspended Cu particles. A prototype demonstration of an ignition DS is planned for 2008, incorporating the needed novel nanomaterials science developments and the required fabrication tolerances for a realistic ignition attempt after 2010

Exponential stability for stochastic delayed recurrent neural networks with mixed time-varying delays and impulses: the continuous-time case

International Nuclear Information System (INIS)

Karthik Raja, U; Leelamani, A; Raja, R; Samidurai, R

2013-01-01

In this paper, the exponential stability for a class of stochastic neural networks with time-varying delays and impulsive effects is considered. By constructing suitable Lyapunov functionals and by using the linear matrix inequality optimization approach, we obtain sufficient delay-dependent criteria to ensure the exponential stability of stochastic neural networks with time-varying delays and impulses. Two numerical examples with simulation results are provided to illustrate the effectiveness of the obtained results over those already existing in the literature. (paper)

Optical resonators for true-time-delay beam steering

Science.gov (United States)

Gesell, Leslie H.; Evanko, Stephen M.

1996-06-01

Conventional true time delay beamforming and steering devices rely on switching between various lengths of delay line. Therefore only discrete delays are possible. Proposed is a new photonics concept for true time delay beamforming which provides a finely controlled continuum of delays with switching speeds on the order of 10's of nanoseconds or faster. The architecture uses an array of waveguide cavities with different resonate frequencies to channelize the signal. Each spectral component of the signal is phase shifted by an amount proportional to the frequency of that component and the desired time delay. These phase shifted spectral components are then summed to obtain the delayed signal. This paper provides an overview of the results of a Phase I SBIR contract where this concept has been refined and analyzed. The parameters for an operational system are determined and indication of the feasibility of this approach is given. Among the issues addressed are the requirements of the resonators and the methods necessary to implement fiber optic Bragg gratings as these resonators.

A comparison of Reactivity Controlled Compression Ignition (RCCI) and Gasoline Compression Ignition (GCI) strategies at high load, low speed conditions

International Nuclear Information System (INIS)

Kavuri, Chaitanya; Paz, Jordan; Kokjohn, Sage L.

2016-01-01

Highlights: • Targeting high load-low speed, optimizations of RCCI and GCI strategies were performed. • The two strategies were compared in terms of performance, controllability and stability. • The optimum cases had high gross indicated efficiency (∼47%) and low NOx emissions. • RCCI strategy showed better combustion control but had higher soot emissions. • GCI strategy was relatively more sensitive to fluctuations in charge conditions. - Abstract: Past research has shown that Reactivity Controlled Compression Ignition (RCCI) and Gasoline Compression Ignition (GCI) combustion are promising approaches to improve efficiency and reduce pollutant emissions. However, the benefits have generally been confined to mid-load operating conditions. To enable practical application, these approaches must be able to operate over the entire engine map. A particularly challenging area is high load, low speed operation. Accordingly, the present work uses detailed CFD modeling and engine experiments to compare RCCI and GCI combustion strategies at a high load, low speed condition. Computational optimizations of RCCI and GCI combustion were performed at 20 bar gross indicated mean effective pressure (IMEP) and 1300 rev/min. The optimum points from the two combustion strategies were verified using engine experiments and were used to make the comparisons between RCCI and GCI combustion. The comparison showed that both the strategies had very similar combustion characteristics with a near top dead center injection initiating combustion. A parametric study was performed to identify the key input parameters that control combustion for the RCCI and GCI strategies. For both strategies, the combustion phasing could be controlled by the start of injection (SOI) timing of the near TDC injection. The short ignition delay of diesel fuel gave the RCCI strategy better control over combustion than the GCI strategy, but also had a simultaneous tradeoff with soot emissions. With the GCI

Controlling flow time delays in flexible manufacturing cells

NARCIS (Netherlands)

Slomp, J.; Caprihan, R.; Bokhorst, J. A. C.

2009-01-01

Flow time delays in Flexible Manufacturing Cells (FMCs) are caused by transport and clamping/reclamping activities. This paper shows how dynamic scheduling parameters may control the flow times of jobs and the available task windows for flow time delays.

Lubricant induced pre-ignition in an optical spark-ignition engine

OpenAIRE

Dingle, Simon Frederick

2014-01-01

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London This work focuses on the introduction of lubricant into the combustion chamber and the effect that this has on pre-ignition. Apparently for the first time, the work presented provides detailed full-bore optical data for lubricant induced pre-ignition and improves understanding of the super-knock phenomena that affects modern downsized gasoline engines. A new single-cylinder optical r...

Truncated predictor feedback for time-delay systems

CERN Document Server

Zhou, Bin

2014-01-01

This book provides a systematic approach to the design of predictor based controllers for (time-varying) linear systems with either (time-varying) input or state delays. Differently from those traditional predictor based controllers, which are infinite-dimensional static feedback laws and may cause difficulties in their practical implementation, this book develops a truncated predictor feedback (TPF) which involves only finite dimensional static state feedback. Features and topics: A novel approach referred to as truncated predictor feedback for the stabilization of (time-varying) time-delay systems in both the continuous-time setting and the discrete-time setting is built systematically Semi-global and global stabilization problems of linear time-delay systems subject to either magnitude saturation or energy constraints are solved in a systematic manner Both stabilization of a single system and consensus of a group of systems (multi-agent systems) are treated in a unified manner by applying the truncated pre...

Central ignition scenarios for TFTR

International Nuclear Information System (INIS)

Zweben, S.J.; Redi, M.H.; Bateman, G.

1986-03-01

The possibility of obtaining ignition in TFTR by means of very centrally peaked density profiles is examined. It is shown that local central alpha heating can be made to exceed local central energy losses (''central ignition'') under global conditions for which Q greater than or equal to 1. Time dependent 1-D transport simulations show that the normal global ignition requirements are substantially relaxed for plasmas with peaked density profiles. 18 refs., 18 figs

Delay-dependent stability of neural networks of neutral type with time delay in the leakage term

International Nuclear Information System (INIS)

Li, Xiaodi; Cao, Jinde

2010-01-01

This paper studies the global asymptotic stability of neural networks of neutral type with mixed delays. The mixed delays include constant delay in the leakage term (i.e. 'leakage delay'), time-varying delays and continuously distributed delays. Based on the topological degree theory, Lyapunov method and linear matrix inequality (LMI) approach, some sufficient conditions are derived ensuring the existence, uniqueness and global asymptotic stability of the equilibrium point, which are dependent on both the discrete and distributed time delays. These conditions are expressed in terms of LMI and can be easily checked by the MATLAB LMI toolbox. Even if there is no leakage delay, the obtained results are less restrictive than some recent works. It can be applied to neural networks of neutral type with activation functions without assuming their boundedness, monotonicity or differentiability. Moreover, the differentiability of the time-varying delay in the non-neutral term is removed. Finally, two numerical examples are given to show the effectiveness of the proposed method

A ‘frozen electric-field’ approach to simulate repetitively pulsed nanosecond plasma discharges and ignition of hydrogen–air mixtures

International Nuclear Information System (INIS)

Nagaraja, Sharath; Yang, Vigor

2014-01-01

High-fidelity modelling of nanosecond repetitively pulsed discharges (NRPDs) is burdened by the multiple time and length scales and large chemistry mechanisms involved, which prohibit detailed analyses and parametric studies. In the present work, we propose a ‘frozen electric-field’ modelling approach to expedite the NRPD simulations without adverse effects on the solution accuracy. First, a burst of nanosecond voltage pulses is simulated self-consistently until the discharge reaches a stationary state. The calculated spatial distributions and temporal evolution of the electric field, electron density and electron energy during the last pulse are then stored in a library and the electrical characteristics of subsequent pulses are frozen at these values. This strategy allows the timestep for numerical integration to be increased by four orders of magnitude (from 10 −13 to 10 −9  s), thereby significantly improving the computational efficiency of the process. Reduced calculations of a burst of 50 discharge pulses show good agreement with the predictions from a complete plasma model (electrical characteristics calculated during each pulse). The error in species densities is less than 20% at the centre of the discharge volume and about 30% near the boundaries. The deviations in temperature, however, are much lower, at 5% in the entire domain. The model predictions are in excellent agreement with measured ignition delay times and temperatures in H 2 –air mixtures subject to dielectric barrier NRPD over a pressure range of 54–144 Torr with equivalence ratios of 0.7–1.2. The OH density increases with pressure and triggers low-temperature fuel oxidation, which leads to rapid temperature rise and ignition. The ignition delay decreases by a factor of 2, with an increase in pressure from 54 to 144 Torr. In contrast, an increase in the H 2 –air equivalence ratio from 0.7 to 1.2 marginally decreases the ignition delay by about 20%. This behaviour is

4-channel time delayed pulse generator

International Nuclear Information System (INIS)

Wetzel, L.F.S.; Rossi, J.O.; Del Bosco, E.

1987-02-01

It is described the project of a 4-channel delayed pulse generator employed to trigger the plasma centrifuge experiment of the Laboratorio Associado de Plasmas. The circuit delivers pulses with amplitude of 15V, full width at half maximum of 50μs and rise time of 0.7μs. The maximum time delay is 100ms. There are two channels with a fine adjustment of 0-1ms. The system can be manually or automatically driven. (author) [pt

Delay time and Hartman effect in strain engineered graphene

International Nuclear Information System (INIS)

Chen, Xi; Deng, Zhi-Yong; Ban, Yue

2014-01-01

Tunneling times, including group delay and dwell time, are studied for massless Dirac electrons transmitting through a one-dimensional barrier in strain-engineered graphene. The Hartman effect, the independence of group delay on barrier length, is induced by the strain effect, and associated with the transmission gap and the evanescent mode. The influence of barrier height/length and strain modulus/direction on the group delay is also discussed, which provides the flexibility to control the group delay with applications in graphene-based devices. The relationship between group delay and dwell time is finally derived to clarify the nature of the Hartman effect

Finite-Time Stability of Large-Scale Systems with Interval Time-Varying Delay in Interconnection

Directory of Open Access Journals (Sweden)

T. La-inchua

2017-01-01

Full Text Available We investigate finite-time stability of a class of nonlinear large-scale systems with interval time-varying delays in interconnection. Time-delay functions are continuous but not necessarily differentiable. Based on Lyapunov stability theory and new integral bounding technique, finite-time stability of large-scale systems with interval time-varying delays in interconnection is derived. The finite-time stability criteria are delays-dependent and are given in terms of linear matrix inequalities which can be solved by various available algorithms. Numerical examples are given to illustrate effectiveness of the proposed method.

Delay-Dependent Guaranteed Cost H∞ Control of an Interval System with Interval Time-Varying Delay

Directory of Open Access Journals (Sweden)

Zhongke Shi

2009-01-01

Full Text Available This paper concerns the problem of the delay-dependent robust stability and guaranteed cost H∞ control for an interval system with time-varying delay. The interval system with matrix factorization is provided and leads to less conservative conclusions than solving a square root. The time-varying delay is assumed to belong to an interval and the derivative of the interval time-varying delay is not a restriction, which allows a fast time-varying delay; also its applicability is broad. Based on the Lyapunov-Ktasovskii approach, a delay-dependent criterion for the existence of a state feedback controller, which guarantees the closed-loop system stability, the upper bound of cost function, and disturbance attenuation lever for all admissible uncertainties as well as out perturbation, is proposed in terms of linear matrix inequalities (LMIs. The criterion is derived by free weighting matrices that can reduce the conservatism. The effectiveness has been verified in a number example and the compute results are presented to validate the proposed design method.

Probability of ignition - a better approach than ignition margin

International Nuclear Information System (INIS)

Ho, S.K.; Perkins, L.J.

1989-01-01

The use of a figure of merit - the probability of ignition - is proposed for the characterization of the ignition performance of projected ignition tokamaks. Monte Carlo and analytic models have been developed to compute the uncertainty distribution function for ignition of a given tokamak design, in terms of the uncertainties inherent in the tokamak physics database. A sample analysis with this method indicates that the risks of not achieving ignition may be unacceptably high unless the accepted margins for ignition are increased. (author). Letter-to-the-editor. 12 refs, 2 figs, 2 tabs

Real-time traffic signal optimization model based on average delay time per person

Directory of Open Access Journals (Sweden)

Pengpeng Jiao

2015-10-01

Full Text Available Real-time traffic signal control is very important for relieving urban traffic congestion. Many existing traffic control models were formulated using optimization approach, with the objective functions of minimizing vehicle delay time. To improve people’s trip efficiency, this article aims to minimize delay time per person. Based on the time-varying traffic flow data at intersections, the article first fits curves of accumulative arrival and departure vehicles, as well as the corresponding functions. Moreover, this article transfers vehicle delay time to personal delay time using average passenger load of cars and buses, employs such time as the objective function, and proposes a signal timing optimization model for intersections to achieve real-time signal parameters, including cycle length and green time. This research further implements a case study based on practical data collected at an intersection in Beijing, China. The average delay time per person and queue length are employed as evaluation indices to show the performances of the model. The results show that the proposed methodology is capable of improving traffic efficiency and is very effective for real-world applications.

Electronic ignition system for internal combustion engines

Energy Technology Data Exchange (ETDEWEB)

Crowder, L W

1980-11-20

Mechanical ignition adjustment devices are sensitive to many effects, for example breakage, faults due to manufacturing tolerances, play in the linkage and the effect of a dirty or corrosive environment. It is therefore the purpose of the invention to provide an electronic ignition system which avoids the disadvantages of a mechanical system. The invention provides adjustment of the ignition point, which gives advance of the ignition timing with increasing speed. An output signal is formed, which supersedes the signal supplied by the electronic control system, so that the ignition is advanced. This also occurs with a larger crankshaft angle before top dead centre of the engine. The electronic control system combines with a source of AC time signals which has a generator as electrical transmitter and a DC battery and ignition coil. The rotor of the electrical generator is driven synchronised with the engine. Structural and functional details of the transistor control circuits are given in 5 patent claims.

The internal propagation of fusion flame with the strong shock of a laser driven plasma block for advanced nuclear fuel ignition

International Nuclear Information System (INIS)

Malekynia, B.; Razavipour, S. S.

2013-01-01

An accelerated skin layer may be used to ignite solid state fuels. Detailed analyses were clarified by solving the hydrodynamic equations for nonlinear force driven plasma block ignition. In this paper, the complementary mechanisms are included for the advanced fuel ignition: external factors such as lasers, compression, shock waves, and sparks. The other category is created within the plasma fusion as reheating of an alpha particle, the Bremsstrahlung absorption, expansion, conduction, and shock waves generated by explosions. With the new condition for the control of shock waves, the spherical deuterium-tritium fuel density should be increased to 75 times that of the solid state. The threshold ignition energy flux density for advanced fuel ignition may be obtained using temperature equations, including the ones for the density profile obtained through the continuity equation and the expansion velocity for the r ≠ 0 layers. These thresholds are significantly reduced in comparison with the ignition thresholds at x = 0 for solid advanced fuels. The quantum correction for the collision frequency is applied in the case of the delay in ion heating. Under the shock wave condition, the spherical proton-boron and proton-lithium fuel densities should be increased to densities 120 and 180 times that of the solid state. These plasma compressions are achieved through a longer duration laser pulse or X-ray. (physics of gases, plasmas, and electric discharges)

Autoignition of straight-run naphtha: A promising fuel for advanced compression ignition engines

KAUST Repository

Alabbad, Mohammed; Issayev, Gani; Badra, Jihad; Voice, Alexander K.; Giri, Binod; Djebbi, Khalil; Ahmed, Ahfaz; Sarathy, Mani; Farooq, Aamir

2017-01-01

Naphtha, a low-octane distillate fuel, has been proposed as a promising low-cost fuel for advanced compression ignition engine technologies. Experimental and modelling studies have been conducted in this work to assess autoignition characteristics of naphtha for use in advanced engines. Ignition delay times of a certified straight-run naphtha fuel, supplied by Haltermann Solutions, were measured in a shock tube and a rapid comparison machine over wide ranges of experimental conditions (20 and 60 bar, 620–1223 K, ϕ = 0.5, 1 and 2). The Haltermann straight-run naphtha (HSRN) has research octane number (RON) of 60 and motor octane number (MON) of 58.3, with carbon range spanning C3–C9. Reactivity of HSRN was compared, via experiments and simulations, with three suitably formulated surrogates: a two-component PRF (n-heptane/iso-octane) surrogate, a three-component TPRF (toluene/n-heptane/iso-octane) surrogate, and a six-component surrogate. All surrogates reasonably captured the ignition delays of HSRN at high and intermediate temperatures. However, at low temperatures (T < 750 K), the six-component surrogate performed the best in emulating the reactivity of naphtha fuel. Temperature sensitivity and rate of production analyses revealed that the presence of cyclo-alkanes in naphtha inhibits the overall fuel reactivity. Zero-dimensional engine simulations showed that PRF is a good autoignition surrogate for naphtha at high engine loads, however, the six-component surrogate is needed to match the combustion phasing of naphtha at low engine loads.

Autoignition of straight-run naphtha: A promising fuel for advanced compression ignition engines

KAUST Repository

Alabbad, Mohammed

2017-11-24

Naphtha, a low-octane distillate fuel, has been proposed as a promising low-cost fuel for advanced compression ignition engine technologies. Experimental and modelling studies have been conducted in this work to assess autoignition characteristics of naphtha for use in advanced engines. Ignition delay times of a certified straight-run naphtha fuel, supplied by Haltermann Solutions, were measured in a shock tube and a rapid comparison machine over wide ranges of experimental conditions (20 and 60 bar, 620–1223 K, ϕ = 0.5, 1 and 2). The Haltermann straight-run naphtha (HSRN) has research octane number (RON) of 60 and motor octane number (MON) of 58.3, with carbon range spanning C3–C9. Reactivity of HSRN was compared, via experiments and simulations, with three suitably formulated surrogates: a two-component PRF (n-heptane/iso-octane) surrogate, a three-component TPRF (toluene/n-heptane/iso-octane) surrogate, and a six-component surrogate. All surrogates reasonably captured the ignition delays of HSRN at high and intermediate temperatures. However, at low temperatures (T < 750 K), the six-component surrogate performed the best in emulating the reactivity of naphtha fuel. Temperature sensitivity and rate of production analyses revealed that the presence of cyclo-alkanes in naphtha inhibits the overall fuel reactivity. Zero-dimensional engine simulations showed that PRF is a good autoignition surrogate for naphtha at high engine loads, however, the six-component surrogate is needed to match the combustion phasing of naphtha at low engine loads.

An Experimental and Numerical Study of N-Dodecane/Butanol Blends for Compression Ignition Engines

KAUST Repository

Wakale, Anil Bhaurao; Mohamed, Samah; Naser, Nimal; Jaasim, Mohammed; Banerjee, Raja; Im, Hong G.; Sarathy, Mani

2018-01-01

Alcohols are potential blending agents for diesel that can be effectively used in compression ignition engines. This work investigates the use of n-butanol as a blending component for diesel fuel using experiments and simulations. Dodecane was selected as a surrogate for diesel fuel and various concentrations of n-butanol were added to study ignition characteristics. Ignition delay times for different n-butanol/dodecane blends were measured using the ignition quality tester at KAUST (KR-IQT). The experiments were conducted at pressure of 21 and 18 bar, temperature ranging from 703-843 K and global equivalence ratio of 0.85. A skeletal mechanism for n-dodecane and n-butanol blends with 203 species was developed for numerical simulations. The mechanism was developed by combining n-dodecane skeletal mechanism containing 106 species and a detailed mechanism for all the butanol isomers. The new mixture mechanism was validated for various pressure, temperature and equivalence ratio using a 0-D homogeneous reactor model from CHEMKIN for pure base fuels (n-dodecane and butanol). Computational fluid dynamics (CFD) code, CONVERGE was used to further validate the new mechanism. The new mechanism was able to reproduce the experimental results from IQT at different pressure and temperature conditions.

An Experimental and Numerical Study of N-Dodecane/Butanol Blends for Compression Ignition Engines

KAUST Repository

Wakale, Anil Bhaurao

2018-04-03

Alcohols are potential blending agents for diesel that can be effectively used in compression ignition engines. This work investigates the use of n-butanol as a blending component for diesel fuel using experiments and simulations. Dodecane was selected as a surrogate for diesel fuel and various concentrations of n-butanol were added to study ignition characteristics. Ignition delay times for different n-butanol/dodecane blends were measured using the ignition quality tester at KAUST (KR-IQT). The experiments were conducted at pressure of 21 and 18 bar, temperature ranging from 703-843 K and global equivalence ratio of 0.85. A skeletal mechanism for n-dodecane and n-butanol blends with 203 species was developed for numerical simulations. The mechanism was developed by combining n-dodecane skeletal mechanism containing 106 species and a detailed mechanism for all the butanol isomers. The new mixture mechanism was validated for various pressure, temperature and equivalence ratio using a 0-D homogeneous reactor model from CHEMKIN for pure base fuels (n-dodecane and butanol). Computational fluid dynamics (CFD) code, CONVERGE was used to further validate the new mechanism. The new mechanism was able to reproduce the experimental results from IQT at different pressure and temperature conditions.

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Energy Technology Data Exchange (ETDEWEB)

Korakianitis, T.; Namasivayam, A.M.; Crookes, R.J. [School of Engineering and Materials Science, Queen Mary University of London (United Kingdom)

2011-02-15

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO{sub x}) emissions, while producing lower emissions of carbon dioxide (CO{sub 2}), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO{sub x} emissions. High NO{sub x} emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO{sub x} and CO{sub 2} emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is

Visualizing ignition and combustion of methanol mixtures in a diesel engine; Methanol funmu no glow chakka to nensho no kashika

Energy Technology Data Exchange (ETDEWEB)

Inomoto, Y; Harada, T; Kusaka, J; Daisho, Y; Kihara, R; Saito, T [Waseda University, Tokyo (Japan)

1997-10-01

A glow-assisted ignition system tends to suffer from poor ignitability and slow flame propagation at low load in a direct-injection diesel engine fueled with methanol. To investigate the ignition process and improve such disadvantages, methanol sprays, their ignition and flames were visualized at high pressures and temperatures using a modified two-stroke engine. The results show that parameters influencing ignition, the location of a glow-plug, swirl level, pressure and temperature are important. In addition, a full kinetics calculation was conducted to predict the delay of methanol mixture ignition by taking into account 39 chemical species and 157 elementary reactions. 3 refs., 9 figs.

Impulsive control of time-delay systems using delayed impulse and its application to impulsive master-slave synchronization

International Nuclear Information System (INIS)

Sun Jitao; Han Qinglong; Jiang Xiefu

2008-01-01

This Letter is concerned with impulsive control of a class of nonlinear time-delay systems. Some uniform stability criteria for the closed-loop time-delay system under delayed impulsive control are derived by using piecewise Lyapunov functions. Then the criteria are applied to impulsive master-slave synchronization of some secure communication systems with transmission delays and sample delays under delayed impulsive control. Two numerical examples are given to illustrate the effectiveness of the derived results

Ignition Delay Properties of Alternative Fuels with Navy-Relevant Diesel Injectors

Science.gov (United States)

2014-06-01

nozzle tip. 8 Figure 3 EMD injector cross-sectional view, after [15]. c. Sturman Injector A Sturman research diesel injector was used to validate...PROPERTIES OF ALTERNATIVE FUELS WITH NAVY-RELEVANT DIESEL INJECTORS by Andrew J. Rydalch June 2014 Thesis Advisor: Christopher M. Brophy...Navy’s Green Fleet Initiative, this thesis researched the ignition characteristics for diesel replacement fuels used with Navy-relevant fuel injectors

Robust control of time-delay chaotic systems

International Nuclear Information System (INIS)

Hua Changchun; Guan Xinping

2003-01-01

Robust control problem of nonlinear time-delay chaotic systems is investigated. For such uncertain systems, we propose adaptive feedback controller and novel nonlinear feedback controller. They are both independent of the time delay and can render the corresponding closed-loop systems globally uniformly ultimately bounded stable. The simulations on controlling logistic system are made and the results show the controllers are feasible

Experimental characterization of diesel ignition and lift-off length using a single-hole ECN injector

International Nuclear Information System (INIS)

Benajes, Jesús; Payri, Raúl; Bardi, Michele; Martí-Aldaraví, Pedro

2013-01-01

In this work, lift-off length and ignition delay have been measured via chemiluminescence techniques in a wide range of conditions for a single-hole injector from the Engine Combustion Network (ECN) dataset and using a single component fuel (n-dodecane). In addition, Schlieren technique was used to characterize the ignition event using a new developed post-processing methodology capable of characterizing the “disappearance” phenomenon linked to the start of cool flames. Experiments have been carried out in a novel constant-pressure flow facility able of reproducing engine-like thermodynamic conditions. Results show that oxygen concentration seems to have a negligible impact on the start of cool flames. Empirical correlations have been obtained for the three measured parameters and they manifest similar trends of other previously published correlations for lift-off length and second stage ignition. These correlations also underline that the effect of oxygen concentration and ambient density is caught differently by chemiluminescence and Schlieren techniques, even though the absolute value of the measurements remains close. -- Highlights: • Ignition delay and LOL of an ECN injector are measured using the ECN standard diagnostics. • A novel processing is developed for Schlieren images to determine first and second stage ignition. • A sweep of injection pressure, density, temperature and oxygen concentration is performed. • A statistical analysis is done to provide an analytical description of the results

Novel delay-distribution-dependent stability analysis for continuous-time recurrent neural networks with stochastic delay

International Nuclear Information System (INIS)

Wang Shen-Quan; Feng Jian; Zhao Qing

2012-01-01

In this paper, the problem of delay-distribution-dependent stability is investigated for continuous-time recurrent neural networks (CRNNs) with stochastic delay. Different from the common assumptions on time delays, it is assumed that the probability distribution of the delay taking values in some intervals is known a priori. By making full use of the information concerning the probability distribution of the delay and by using a tighter bounding technique (the reciprocally convex combination method), less conservative asymptotic mean-square stable sufficient conditions are derived in terms of linear matrix inequalities (LMIs). Two numerical examples show that our results are better than the existing ones. (general)

Estimation of time-delayed mutual information and bias for irregularly and sparsely sampled time-series

International Nuclear Information System (INIS)

Albers, D.J.; Hripcsak, George

2012-01-01

Highlights: ► Time-delayed mutual information for irregularly sampled time-series. ► Estimation bias for the time-delayed mutual information calculation. ► Fast, simple, PDF estimator independent, time-delayed mutual information bias estimate. ► Quantification of data-set-size limits of the time-delayed mutual calculation. - Abstract: A method to estimate the time-dependent correlation via an empirical bias estimate of the time-delayed mutual information for a time-series is proposed. In particular, the bias of the time-delayed mutual information is shown to often be equivalent to the mutual information between two distributions of points from the same system separated by infinite time. Thus intuitively, estimation of the bias is reduced to estimation of the mutual information between distributions of data points separated by large time intervals. The proposed bias estimation techniques are shown to work for Lorenz equations data and glucose time series data of three patients from the Columbia University Medical Center database.

Pulse heating and ignition for off-centre ignited targets

International Nuclear Information System (INIS)

Mahdy, A.I.; Takabe, H.; Mima, K.

1999-01-01

An off-centre ignition model has been used to study the ignition conditions for laser targets related to the fast ignition scheme. A 2-D hydrodynamic code has been used, including alpha particle heating. The main goal of the study is the possibility of obtaining a high gain ICF target with fast ignition. In order to determine the ignition conditions, samples with various compressed core densities having different spark density-radius product (i.e. areal density) values were selected. The study was carried out in the presence of an external heating source, with a constant heating rate. A dependence of the ignition conditions on the heating rate of the external pulse is demonstrated. For a given set of ignition conditions, our simulation showed that an 11 ps pulse with 17 kJ of injected energy into the spark area was required to achieve ignition for a compressed core with a density of 200 g/cm 3 and 0.5 g/cm 2 spark areal density. It is shown that the ignition conditions are highly dependent on the heating rate of the external pulse. (author)

Robustness studies of ignition targets for the National Ignition Facility in two dimensions

International Nuclear Information System (INIS)

Clark, Daniel S.; Haan, Steven W.; Salmonson, Jay D.

2008-01-01

Inertial confinement fusion capsules are critically dependent on the integrity of their hot spots to ignite. At the time of ignition, only a certain fractional perturbation of the nominally spherical hot spot boundary can be tolerated and the capsule still achieve ignition. The degree to which the expected hot spot perturbation in any given capsule design is less than this maximum tolerable perturbation is a measure of the ignition margin or robustness of that design. Moreover, since there will inevitably be uncertainties in the initial character and implosion dynamics of any given capsule, all of which can contribute to the eventual hot spot perturbation, quantifying the robustness of that capsule against a range of parameter variations is an important consideration in the capsule design. Here, the robustness of the 300 eV indirect drive target design for the National Ignition Facility [Lindl et al., Phys. Plasmas 11, 339 (2004)] is studied in the parameter space of inner ice roughness, implosion velocity, and capsule scale. A suite of 2000 two-dimensional simulations, run with the radiation hydrodynamics code LASNEX, is used as the data base for the study. For each scale, an ignition region in the two remaining variables is identified and the ignition cliff is mapped. In accordance with the theoretical arguments of Levedahl and Lindl [Nucl. Fusion 37, 165 (1997)] and Kishony and Shvarts [Phys. Plasmas 8, 4925 (2001)], the location of this cliff is fitted to a power law of the capsule implosion velocity and scale. It is found that the cliff can be quite well represented in this power law form, and, using this scaling law, an assessment of the overall (one- and two-dimensional) ignition margin of the design can be made. The effect on the ignition margin of an increase or decrease in the density of the target fill gas is also assessed

Laser imprint and implications for direct drive ignition with the National Ignition Facility

International Nuclear Information System (INIS)

Weber, S.V.; Glendinning, S.G.; Kalantar, D.H.; Remington, B.A.; Rothenberg, J.E.

1996-01-01

For direct drive ICF, nonuniformities in laser illumination can seed ripples at the ablation front in a process called imprint. Such nonuniformities will grow during the capsule implosion and can penetrate the capsule shell impede ignition, or degrade burn. We have simulated imprint for a number of experiments on tile Nova laser. Results are in generally good agreement with experimental data. We leave also simulated imprint upon National Ignition Facility (NIF) direct drive ignition capsules. Imprint modulation amplitude comparable to the intrinsic surface finish of ∼40 nm is predicted for a laser bandwidth of 0.5 THz. Ablation front modulations experience growth factors up to several thousand, carrying modulation well into the nonlinear regime. Saturation modeling predicts that the shell should remain intact at the time of peak velocity, but penetration at earlier times appears more marginal

Ignition in the next step tokamak

International Nuclear Information System (INIS)

Johner, J.

1990-07-01

A 1/2-D model for thermal equilibrium of a thermonuclear plasma with transport described by an empirical global energy confinement time is described. Ignition in NET and ITER is studied for a number of energy confinement time scaling expressions. Ignited operation of these machines at the design value of the neutron wall load is shown to satisfy both beta and density constraints. The value of the confinement time enhancement factor required for such operation is found to be lower for the more recently proposed scaling expressions than it is for the oldest ones. With such new scalings, ignition could be obtained in H-mode in NET and ITER even with relatively flat density profiles

Overview of the Compact Ignition Tokamak

International Nuclear Information System (INIS)

Flanagan, C.A.

1986-01-01

The mission of CIT is to realize, study, and optimize fully ignited plasma discharges. The physics requirements have been established to provide reasonable assurance that the mission will be achieved: (1) plasma confinement guidelines consider all present scaling laws; ohmic, auxiliary heated L-mode, auxiliary heated H-mode, (2) figure-of-merit established: X = aB/q; this is proportional to ignition margin; X must be >25, (3) burn pulse duration set at ten times tau-E; an additional two times tau-E specified to heat to ignition, and (4) capability to operate both in limiter and divertor mode

Ignition and time-dependent fractional power operation of tokamak reactors

International Nuclear Information System (INIS)

Vold, E.L.; Mau, T.K.; Conn, R.W.

1986-01-01

The eventual utilization of a tokamak fusion reactor for commercial power necessitates a thorough understanding of the operational requirements at full and fractional power levels and during transitions from one operating level to another. In this study we examine the role of burn control in maintaining the reactor plasma at equilibrium to avoid thermal runaway during fractional power operation. Because these requirements rely so heavily on the assumptions that govern the plasma transport, this study focuses on time-dependent analyses and a comparison of ignition requirements using a range of energy confinement

Radiative Ignition of fine-ammonium perchlorate composite propellants

Energy Technology Data Exchange (ETDEWEB)

Cain, Jeremy; Brewster, M. Quinn [Department of Mechanical Science and Industrial Engineering, University of Illinois, Urbana, IL 61801 (United States)

2006-08-15

Radiative ignition of quasi-homogeneous mixtures of ammonium perchlorate (AP) and hydroxyterminated polybutadiene (HTPB) binder has been investigated experimentally. Solid propellants consisting of fine AP (2 {mu}m) and HTPB binder ({proportional_to}76/24% by mass) were ignited by CO{sub 2} laser radiation. The lower boundary of a go/no-go ignition map (minimum ignition time vs. heat flux) was obtained. Opacity was varied by adding carbon black up to 1% by mass. Ignition times ranged from 0.78 s to 0.076 s for incident fluxes ranging from 60 W/cm{sup 2} to 400 W/cm{sup 2}. It was found that AP and HTPB are sufficiently strongly absorbing of 10.6 {mu}m CO{sub 2} laser radiation (absorption coefficient {approx}250 cm{sup -1}) so that the addition of carbon black in amounts typical of catalysts or opacitymodifying agents (up to 1%) would have only a small influence on radiative ignition times at 10.6 {mu}m. A simple theoretical analysis indicated that the ignition time-flux data are consistent with in-depth absorption effects. Furthermore, this analysis showed that the assumption of surface absorption is not appropriate, even for this relatively opaque system. For broadband visible/near-infrared radiation, such as from burning metal/oxide particle systems, the effects of in-depth absorption would probably be even stronger. (Abstract Copyright [2006], Wiley Periodicals, Inc.)

Stability of Nonlinear Systems with Unknown Time-varying Feedback Delay

Science.gov (United States)

Chunodkar, Apurva A.; Akella, Maruthi R.

2013-12-01

This paper considers the problem of stabilizing a class of nonlinear systems with unknown bounded delayed feedback wherein the time-varying delay is 1) piecewise constant 2) continuous with a bounded rate. We also consider application of these results to the stabilization of rigid-body attitude dynamics. In the first case, the time-delay in feedback is modeled specifically as a switch among an arbitrarily large set of unknown constant values with a known strict upper bound. The feedback is a linear function of the delayed states. In the case of linear systems with switched delay feedback, a new sufficiency condition for average dwell time result is presented using a complete type Lyapunov-Krasovskii (L-K) functional approach. Further, the corresponding switched system with nonlinear perturbations is proven to be exponentially stable inside a well characterized region of attraction for an appropriately chosen average dwell time. In the second case, the concept of the complete type L-K functional is extended to a class of nonlinear time-delay systems with unknown time-varying time-delay. This extension ensures stability robustness to time-delay in the control design for all values of time-delay less than the known upper bound. Model-transformation is used in order to partition the nonlinear system into a nominal linear part that is exponentially stable with a bounded perturbation. We obtain sufficient conditions which ensure exponential stability inside a region of attraction estimate. A constructive method to evaluate the sufficient conditions is presented together with comparison with the corresponding constant and piecewise constant delay. Numerical simulations are performed to illustrate the theoretical results of this paper.

A fundamental investigation into the relationship between lubricant composition and fuel ignition quality

KAUST Repository

Kuti, Olawole Abiola

2015-11-01

A fundamental experiment involving the use of an ignition quality tester (IQT) was carried out to elucidate the effects of lubricant oil composition which could lead to low speed pre-ignition (LSPI) processes in direct injection spark ignition (DISI) engines. Prior to the IQT tests, lubricant base oils were analyzed using ultra-high resolution mass spectrometry to reveal their molecular composition. High molecular-weight hydrocarbons such as nC16H34, nC17H36, and nC18H38 were selected as surrogates of lubricant base oil constituents, and then mixed with iso-octane (iC8H18-gasoline surrogate) in proportions of 1 vol.% (iC8H18 = 99 vol.%) and 10 vol.% (iC8H18 = 90 vol.%) for the IQT experiments. In addition, lubricant base oils such as SN100 (Group I) and HC4 and HC6 (Group III) and a fully formulated lubricant (SAE 20W50) were mixed with iso-octane in the same proportions. The IQT results were conducted at an ambient pressure of 15 bar and a temperature range of 680-873 K. In the temperature range of 710-850 K, the addition of 10 vol.% base oils surrogates, base oils, and lubricating oil to the 90 vol.% iC8H18 reduces the average total ignition delay time by up to 54% for all mixtures, while the addition of 1 vol.% to 99 vol.% iC8H18 yielded a 7% reduction within the same temperature range. The shorter total ignition delay was attributed to the higher reactivity of the lubricant base oil constituents in the fuel mixtures. A correlation between reactivity of base oils and their molecular composition was tentatively established. These results suggest that the lubricants have the propensity of initiating LSPI in DISI engines. Furthermore, similar results for n-alkanes, lubricant base oils, and fully formulated commercial lubricants suggest that it is the hydrocarbon fraction that contributes primarily to enhanced reactivity, and not the inorganic or organometallic additives. © 2015 Elsevier Ltd. All rights reserved.

A fundamental investigation into the relationship between lubricant composition and fuel ignition quality

KAUST Repository

Kuti, Olawole Abiola; Yang, Seung Yeon; Hourani, Nadim; Naser, Nimal; Roberts, William L.; Chung, Suk-Ho; Sarathy, Mani

2015-01-01

A fundamental experiment involving the use of an ignition quality tester (IQT) was carried out to elucidate the effects of lubricant oil composition which could lead to low speed pre-ignition (LSPI) processes in direct injection spark ignition (DISI) engines. Prior to the IQT tests, lubricant base oils were analyzed using ultra-high resolution mass spectrometry to reveal their molecular composition. High molecular-weight hydrocarbons such as nC16H34, nC17H36, and nC18H38 were selected as surrogates of lubricant base oil constituents, and then mixed with iso-octane (iC8H18-gasoline surrogate) in proportions of 1 vol.% (iC8H18 = 99 vol.%) and 10 vol.% (iC8H18 = 90 vol.%) for the IQT experiments. In addition, lubricant base oils such as SN100 (Group I) and HC4 and HC6 (Group III) and a fully formulated lubricant (SAE 20W50) were mixed with iso-octane in the same proportions. The IQT results were conducted at an ambient pressure of 15 bar and a temperature range of 680-873 K. In the temperature range of 710-850 K, the addition of 10 vol.% base oils surrogates, base oils, and lubricating oil to the 90 vol.% iC8H18 reduces the average total ignition delay time by up to 54% for all mixtures, while the addition of 1 vol.% to 99 vol.% iC8H18 yielded a 7% reduction within the same temperature range. The shorter total ignition delay was attributed to the higher reactivity of the lubricant base oil constituents in the fuel mixtures. A correlation between reactivity of base oils and their molecular composition was tentatively established. These results suggest that the lubricants have the propensity of initiating LSPI in DISI engines. Furthermore, similar results for n-alkanes, lubricant base oils, and fully formulated commercial lubricants suggest that it is the hydrocarbon fraction that contributes primarily to enhanced reactivity, and not the inorganic or organometallic additives. © 2015 Elsevier Ltd. All rights reserved.

Improving Delay-Range-Dependent Stability Condition for Systems with Interval Time-Varying Delay

Directory of Open Access Journals (Sweden)

Wei Qian

2013-01-01

Full Text Available This paper discusses the delay-range-dependent stability for systems with interval time-varying delay. Through defining the new Lyapunov-Krasovskii functional and estimating the derivative of the LKF by introducing new vectors, using free matrices and reciprocally convex approach, the new delay-range-dependent stability conditions are obtained. Two well-known examples are given to illustrate the less conservatism of the proposed theoretical results.

Passivity analysis and synthesis for uncertain time-delay systems

Directory of Open Access Journals (Sweden)

Magdi S. Mahmoud

2001-01-01

Full Text Available In this paper, we investigate the robust passivity analysis and synthesis problems for a class of uncertain time-delay systems. This class of systems arises in the modelling effort of studying water quality constituents in fresh stream. For the analysis problem, we derive a sufficient condition for which the uncertain time-delay system is robustly stable and strictly passive for all admissible uncertainties. The condition is given in terms of a linear matrix inequality. Both the delay-independent and delay-dependent cases are considered. For the synthesis problem, we propose an observer-based design method which guarantees that the closed-loop uncertain time-delay system is stable and strictly passive for all admissible uncertainties. Several examples are worked out to illustrate the developed theory.

Time averaging, ageing and delay analysis of financial time series

Science.gov (United States)

Cherstvy, Andrey G.; Vinod, Deepak; Aghion, Erez; Chechkin, Aleksei V.; Metzler, Ralf

2017-06-01

We introduce three strategies for the analysis of financial time series based on time averaged observables. These comprise the time averaged mean squared displacement (MSD) as well as the ageing and delay time methods for varying fractions of the financial time series. We explore these concepts via statistical analysis of historic time series for several Dow Jones Industrial indices for the period from the 1960s to 2015. Remarkably, we discover a simple universal law for the delay time averaged MSD. The observed features of the financial time series dynamics agree well with our analytical results for the time averaged measurables for geometric Brownian motion, underlying the famed Black-Scholes-Merton model. The concepts we promote here are shown to be useful for financial data analysis and enable one to unveil new universal features of stock market dynamics.

Patient delay is the main cause of treatment delay in acute limb ischemia: an investigation of pre- and in-hospital time delay

DEFF Research Database (Denmark)

Londero, Louise Skovgaard; Nørgaard, Birgitte; Houlind, Kim Christian

2014-01-01

Abstract BACKGROUND: The prognosis of acute limb ischemia is severe, with amputation rates of up to 25% and in-hospital mortality of 9-15%. Delay in treatment increases the risk of major amputation and may be present at different stages, including patient delay, doctors´ delay and waiting time...... in the emergency department. It is important to identify existing problems in order to reduce time delay. The aim of this study was to collect data for patients with acute limb ischemia and to evaluate the time delay between the different events from onset of symptoms to specialist evaluation and further treatment...... (median (range)) was identified. From onset of symptoms to first contact with a doctor the time for all patients were 24 (0-1200) hours. Thirty patients needed immediate intervention. In the group of fourteen patients who had immediate operation, the median time from vascular evaluation...

Kalman filtering for time-delayed linear systems

Institute of Scientific and Technical Information of China (English)

LU Xiao; WANG Wei

2006-01-01

This paper is to study the linear minimum variance estimation for discrete- time systems. A simple approach to the problem is presented by developing re-organized innovation analysis for the systems with instantaneous and double time-delayed measurements. It is shown that the derived estimator involves solving three different standard Kalman filtering with the same dimension as the original system. The obtained results form the basis for solving some complicated problems such as H∞ fixed-lag smoothing, preview control, H∞ filtering and control with time delays.

Time delay systems theory, numerics, applications, and experiments

CERN Document Server

Ersal, Tulga; Orosz, Gábor

2017-01-01

This volume collects contributions related to selected presentations from the 12th IFAC Workshop on Time Delay Systems, Ann Arbor, June 28-30, 2015. The included papers present novel techniques and new results of delayed dynamical systems. The topical spectrum covers control theory, numerical analysis, engineering and biological applications as well as experiments and case studies. The target audience primarily comprises research experts in the field of time delay systems, but the book may also be beneficial for graduate students alike. .

Noise-induced coherence in bistable systems with multiple time delays

International Nuclear Information System (INIS)

Jiang Yu; Dong, Shi-Hai; Lozada-Cassou, M.

2004-01-01

We study the correlation properties of noise-driven bistable systems with multiple time-delay feedbacks. For small noisy perturbation and feedback magnitude, we derive the autocorrelation function and the power spectrum based on the two-state model with transition rates depending on the earlier states of the system. A comparison between the single and double time delays reveals that the auto correlation functions exhibit exponential decay with small undulation for the double time delays, in contrast with the remarkable oscillatory behavior at small time lags for the single time delay

Photoemission and photoionization time delays and rates

Science.gov (United States)

Gallmann, L.; Jordan, I.; Wörner, H. J.; Castiglioni, L.; Hengsberger, M.; Osterwalder, J.; Arrell, C. A.; Chergui, M.; Liberatore, E.; Rothlisberger, U.; Keller, U.

2017-01-01

Ionization and, in particular, ionization through the interaction with light play an important role in fundamental processes in physics, chemistry, and biology. In recent years, we have seen tremendous advances in our ability to measure the dynamics of photo-induced ionization in various systems in the gas, liquid, or solid phase. In this review, we will define the parameters used for quantifying these dynamics. We give a brief overview of some of the most important ionization processes and how to resolve the associated time delays and rates. With regard to time delays, we ask the question: how long does it take to remove an electron from an atom, molecule, or solid? With regard to rates, we ask the question: how many electrons are emitted in a given unit of time? We present state-of-the-art results on ionization and photoemission time delays and rates. Our review starts with the simplest physical systems: the attosecond dynamics of single-photon and tunnel ionization of atoms in the gas phase. We then extend the discussion to molecular gases and ionization of liquid targets. Finally, we present the measurements of ionization delays in femto- and attosecond photoemission from the solid–vacuum interface. PMID:29308414

Photoemission and photoionization time delays and rates

Directory of Open Access Journals (Sweden)

L. Gallmann

2017-11-01

Full Text Available Ionization and, in particular, ionization through the interaction with light play an important role in fundamental processes in physics, chemistry, and biology. In recent years, we have seen tremendous advances in our ability to measure the dynamics of photo-induced ionization in various systems in the gas, liquid, or solid phase. In this review, we will define the parameters used for quantifying these dynamics. We give a brief overview of some of the most important ionization processes and how to resolve the associated time delays and rates. With regard to time delays, we ask the question: how long does it take to remove an electron from an atom, molecule, or solid? With regard to rates, we ask the question: how many electrons are emitted in a given unit of time? We present state-of-the-art results on ionization and photoemission time delays and rates. Our review starts with the simplest physical systems: the attosecond dynamics of single-photon and tunnel ionization of atoms in the gas phase. We then extend the discussion to molecular gases and ionization of liquid targets. Finally, we present the measurements of ionization delays in femto- and attosecond photoemission from the solid–vacuum interface.

Relativity time-delay experiments utilizing 'Mariner' spacecraft

Science.gov (United States)

Esposito, P. B.; Anderson, J. D.

1974-01-01

Relativity predicts that the transit time of a signal propagated from the earth to a spacecraft and retransmitted back to earth ought to exhibit an additional, variable time delay. The present work describes some of the analytical techniques employed in experiments using Mariner spacecraft designed to test the accuracy of this prediction. Two types of data are analyzed in these relativity experiments; these include phase-coherent, two-way Doppler shift and round-trip, transit-time measurements. Results of Mariner 6 and 7 relativistic time-delay experiments are in agreement with Einstein's theory of general relativity with an uncertainty of 3%.

Experimental and Numerical Study of Jet Controlled Compression Ignition on Combustion Phasing Control in Diesel Premixed Compression Ignition Systems

Directory of Open Access Journals (Sweden)

Qiang Zhang

2014-07-01

Full Text Available In order to directly control the premixed combustion phasing, a Jet Controlled Compression Ignition (JCCI for diesel premixed compression ignition systems is investigated. Experiments were conducted on a single cylinder natural aspirated diesel engine without EGR at 3000 rpm. Numerical models were validated by load sweep experiments at fixed spark timing. Detailed combustion characteristics were analyzed based on the BMEP of 2.18 bar. The simulation results showed that the high temperature jets of reacting active radical species issued from the ignition chamber played an important role on the onset of combustion in the JCCI system. The combustion of diesel pre-mixtures was initiated rapidly by the combustion products issued from the ignition chamber. Moreover, the flame propagation was not obvious, similar to that in Pre-mixed Charge Compression Ignition (PCCI. Consequently, spark timing sweep experiments were conducted. The results showed a good linear relationship between spark timing in the ignition chamber and CA10 and CA50, which indicated the ability for direct combustion phasing control in diesel PCCI. The NOx and soot emissions gradually changed with the decrease of spark advance angle. The maximum reduction of NOx and soot were both over 90%, and HC and CO emissions were increased.

Effect of flow velocity and temperature on ignition characteristics in laser ignition of natural gas and air mixtures

Science.gov (United States)

Griffiths, J.; Riley, M. J. W.; Borman, A.; Dowding, C.; Kirk, A.; Bickerton, R.

2015-03-01

Laser induced spark ignition offers the potential for greater reliability and consistency in ignition of lean air/fuel mixtures. This increased reliability is essential for the application of gas turbines as primary or secondary reserve energy sources in smart grid systems, enabling the integration of renewable energy sources whose output is prone to fluctuation over time. This work details a study into the effect of flow velocity and temperature on minimum ignition energies in laser-induced spark ignition in an atmospheric combustion test rig, representative of a sub 15 MW industrial gas turbine (Siemens Industrial Turbomachinery Ltd., Lincoln, UK). Determination of minimum ignition energies required for a range of temperatures and flow velocities is essential for establishing an operating window in which laser-induced spark ignition can operate under realistic, engine-like start conditions. Ignition of a natural gas and air mixture at atmospheric pressure was conducted using a laser ignition system utilizing a Q-switched Nd:YAG laser source operating at 532 nm wavelength and 4 ns pulse length. Analysis of the influence of flow velocity and temperature on ignition characteristics is presented in terms of required photon flux density, a useful parameter to consider during the development laser ignition systems.

Start time delays in operating room: Different perspectives

Directory of Open Access Journals (Sweden)

Babita Gupta

2011-01-01

Full Text Available Background: Healthcare expenditure is a serious concern, with escalating costs failing to meet the expectations of quality care. The treatment capacities are limited in a hospital setting and the operating rooms (ORs. Their optimal utilization is vital in efficient hospital management. Starting late means considerable wait time for staff, patients and waste of resources. We planned an audit to assess different perspectives of the residents in surgical specialities and anesthesia and OR staff nurses so as to know the causative factors of operative delay. This can help develop a practical model to decrease start time delays in operating room (ORs. Aims: An audit to assess different perspectives of the Operating room (OR staff with respect to the varied causative factors of operative delay in the OR. To aid in the development of a practical model to decrease start time delays in ORs and facilitate on-time starts at Jai Prakash Narayan Apex Trauma centre (JPNATC, All India Institute of Medical Sciences (AIIMS, New Delhi. Methods: We prepared a questionnaire seeking the five main reasons of delay as per their perspective. Results: The available data was analysed. Analysis of the data demonstrated the common causative factors in start time operative delays as: a lack of proper planning, deficiencies in team work, communication gap and limited availability of trained supporting staff. Conclusions: The preparation of the equipment and required material for the OR cases must be done well in advance. Utilization of newer technology enables timely booking and scheduling of cases. Improved inter-departmental coordination and compliance with preanesthetic instructions needs to be ensured. It is essential that the anesthesiologists perform their work promptly, well in time . and supervise the proceedings as the OR manager. This audit is a step forward in defining the need of effective OR planning for continuous quality improvement.

Miniature free-piston homogeneous charge compression ignition engine-compressor concept - Part II: modeling HCCI combustion in small scales with detailed homogeneous gas phase chemical kinetics

Energy Technology Data Exchange (ETDEWEB)

Aichlmayr, H.T.; Kittelson, D.B.; Zachariah, M.R. [The University of Minnesota, Minneapolis (United States). Departments of Mechanical Engineering and Chemistry

2002-10-01

Operational maps for crankshaft-equipped miniature homogeneous charge compression ignition engines are established using performance estimation, detailed chemical kinetics, and diffusion models for heat transfer and radical loss. In this study, radical loss was found to be insignificant. In contrast, heat transfer was found to be increasingly significant for 10, 1, and 0.1 W engines, respectively. Also, temperature-pressure trajectories and ignition delay time maps are used to explore relationships between engine operational parameters and HCCI. Lastly, effects of engine operating conditions and design on the indicated fuel conversion efficiency are investigated. (author)

Time-delayed feedback control of coherence resonance chimeras

Science.gov (United States)

Zakharova, Anna; Semenova, Nadezhda; Anishchenko, Vadim; Schöll, Eckehard

2017-11-01

Using the model of a FitzHugh-Nagumo system in the excitable regime, we investigate the influence of time-delayed feedback on noise-induced chimera states in a network with nonlocal coupling, i.e., coherence resonance chimeras. It is shown that time-delayed feedback allows for the control of the range of parameter values where these chimera states occur. Moreover, for the feedback delay close to the intrinsic period of the system, we find a novel regime which we call period-two coherence resonance chimera.

Generalized synchronization-based multiparameter estimation in modulated time-delayed systems

Science.gov (United States)

Ghosh, Dibakar; Bhattacharyya, Bidyut K.

2011-09-01

We propose a nonlinear active observer based generalized synchronization scheme for multiparameter estimation in time-delayed systems with periodic time delay. A sufficient condition for parameter estimation is derived using Krasovskii-Lyapunov theory. The suggested tool proves to be globally and asymptotically stable by means of Krasovskii-Lyapunov method. With this effective method, parameter identification and generalized synchronization of modulated time-delayed systems with all the system parameters unknown, can be achieved simultaneously. We restrict our study for multiple parameter estimation in modulated time-delayed systems with single state variable only. Theoretical proof and numerical simulation demonstrate the effectiveness and feasibility of the proposed technique. The block diagram of electronic circuit for multiple time delay system shows that the method is easily applicable in practical communication problems.

Complex Time-Delay Systems Theory and Applications

CERN Document Server

Atay, Fatihcan M

2010-01-01

Time delays in dynamical systems arise as an inevitable consequence of finite speeds of information transmission. Realistic models increasingly demand the inclusion of delays in order to properly understand, analyze, design, and control real-life systems. The goal of this book is to present the state-of-the-art in research on time-delay dynamics in the framework of complex systems and networks. While the mathematical theory of delay equations is quite mature, its application to the particular problems of complex systems and complexity is a newly emerging field, and the present volume aims to play a pioneering role in this perspective. The chapters in this volume are authored by renowned experts and cover both theory and applications in a wide range of fields, with examples extending from neuroscience and biology to laser physics and vehicle traffic. Furthermore, all chapters include sufficient introductory material and extensive bibliographies, making the book a self-contained reference for both students and ...

Introduction to Focus Issue: Time-delay dynamics

Science.gov (United States)

Erneux, Thomas; Javaloyes, Julien; Wolfrum, Matthias; Yanchuk, Serhiy

2017-11-01

The field of dynamical systems with time delay is an active research area that connects practically all scientific disciplines including mathematics, physics, engineering, biology, neuroscience, physiology, economics, and many others. This Focus Issue brings together contributions from both experimental and theoretical groups and emphasizes a large variety of applications. In particular, lasers and optoelectronic oscillators subject to time-delayed feedbacks have been explored by several authors for their specific dynamical output, but also because they are ideal test-beds for experimental studies of delay induced phenomena. Topics include the control of cavity solitons, as light spots in spatially extended systems, new devices for chaos communication or random number generation, higher order locking phenomena between delay and laser oscillation period, and systematic bifurcation studies of mode-locked laser systems. Moreover, two original theoretical approaches are explored for the so-called Low Frequency Fluctuations, a particular chaotical regime in laser output which has attracted a lot of interest for more than 30 years. Current hot problems such as the synchronization properties of networks of delay-coupled units, novel stabilization techniques, and the large delay limit of a delay differential equation are also addressed in this special issue. In addition, analytical and numerical tools for bifurcation problems with or without noise and two reviews on concrete questions are proposed. The first review deals with the rich dynamics of simple delay climate models for El Nino Southern Oscillations, and the second review concentrates on neuromorphic photonic circuits where optical elements are used to emulate spiking neurons. Finally, two interesting biological problems are considered in this Focus Issue, namely, multi-strain epidemic models and the interaction of glucose and insulin for more effective treatment.

New Results on Passivity Analysis of Stochastic Neural Networks with Time-Varying Delay and Leakage Delay

Directory of Open Access Journals (Sweden)

YaJun Li

2015-01-01

Full Text Available The passivity problem for a class of stochastic neural networks systems (SNNs with varying delay and leakage delay has been further studied in this paper. By constructing a more effective Lyapunov functional, employing the free-weighting matrix approach, and combining with integral inequality technic and stochastic analysis theory, the delay-dependent conditions have been proposed such that SNNs are asymptotically stable with guaranteed performance. The time-varying delay is divided into several subintervals and two adjustable parameters are introduced; more information about time delay is utilised and less conservative results have been obtained. Examples are provided to illustrate the less conservatism of the proposed method and simulations are given to show the impact of leakage delay on stability of SNNs.

Gasoline surrogate modeling of gasoline ignition in a rapid compression machine and comparison to experiments

Energy Technology Data Exchange (ETDEWEB)

Mehl, M; Kukkadapu, G; Kumar, K; Sarathy, S M; Pitz, W J; Sung, S J

2011-09-15

-stage (when observed) and second-stage ignition delay times and of heat release rate. The experimental and computational results are used to gain insight into low and intermediate temperature processes during gasoline ignition.

A polar-drive shock-ignition design for the National Ignition Facility

Energy Technology Data Exchange (ETDEWEB)

Anderson, K. S.; McKenty, P. W.; Collins, T. J. B.; Craxton, R. S.; Delettrez, J. A.; Marozas, J. A.; Skupsky, S.; Shvydky, A. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Betti, R. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center, University of Rochester, Rochester, New York 14623 (United States); Departments of Mechanical Engineering and Physics, University of Rochester, Rochester, New York 14627 (United States); Hohenberger, M.; Theobald, W.; Lafon, M.; Nora, R. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623 (United States); Fusion Science Center, University of Rochester, Rochester, New York 14623 (United States)

2013-05-15

Shock ignition [R. Betti et al., Phys. Rev. Lett. 98, 155001 (2007)] is being pursued as a viable option to achieve ignition on the National Ignition Facility (NIF). Shock-ignition target designs use a high-intensity laser spike at the end of a low-adiabat assembly pulse to launch a spherically convergent strong shock to ignite the hot spot of an imploding capsule. A shock-ignition target design for the NIF is presented. One-dimensional simulations indicate an ignition threshold factor of 4.1 with a gain of 58. A polar-drive beam-pointing configuration for shock-ignition experiments on the NIF at 750 kJ is proposed. The capsule design is shown to be robust to the various one- and two-dimensional effects and nonuniformities anticipated on the NIF. The target is predicted to ignite with a gain of 38 when including all anticipated levels of nonuniformity and system uncertainty.

Synchronization of nonidentical chaotic neural networks with leakage delay and mixed time-varying delays

Directory of Open Access Journals (Sweden)

Cao Jinde

2011-01-01

Full Text Available Abstract In this paper, an integral sliding mode control approach is presented to investigate synchronization of nonidentical chaotic neural networks with discrete and distributed time-varying delays as well as leakage delay. By considering a proper sliding surface and constructing Lyapunov-Krasovskii functional, as well as employing a combination of the free-weighting matrix method, Newton-Leibniz formulation and inequality technique, a sliding mode controller is designed to achieve the asymptotical synchronization of the addressed nonidentical neural networks. Moreover, a sliding mode control law is also synthesized to guarantee the reachability of the specified sliding surface. The provided conditions are expressed in terms of linear matrix inequalities, and are dependent on the discrete and distributed time delays as well as leakage delay. A simulation example is given to verify the theoretical results.

The Ignition Target for the National Ignition Facility

International Nuclear Information System (INIS)

Atherton, L J; Moses, E I; Carlisle, K; Kilkenny, J

2007-01-01

The National Ignition Facility (NIF) is a 192 beam Nd-glass laser facility presently under construction at Lawrence Livermore National Laboratory (LLNL) for performing inertial confinement fusion (ICF) and experiments studying high energy density (HED) science. When completed in 2009, NIF will be able to produce 1.8 MJ, 500 TW of ultraviolet light for target experiments that will create conditions of extreme temperatures (>10 8 K), pressures (10-GBar) and matter densities (> 100 g/cm 3 ). A detailed program called the National Ignition Campaign (NIC) has been developed to enable ignition experiments in 2010, with the goal of producing fusion ignition and burn of a deuterium-tritium (DT) fuel mixture in millimeter-scale target capsules. The first of the target experiments leading up to these ignition shots will begin in 2008. Targets for the National Ignition Campaign are both complex and precise, and are extraordinarily demanding in materials fabrication, machining, assembly, cryogenics and characterization. An overview of the campaign for ignition will be presented, along with technologies for target fabrication, assembly and metrology and advances in growth and x-ray imaging of DT ice layers. The sum of these efforts represents a quantum leap in target precision, characterization, manufacturing rate and flexibility over current state-of-the-art

Effect of diesel pre-injection timing on combustion and emission characteristics of compression ignited natural gas engine

International Nuclear Information System (INIS)

Xu, Min; Cheng, Wei; Zhang, Hongfei; An, Tao; Zhang, Shaohua

2016-01-01

Highlights: • Pre-injection timing on combustion and emission of CING engine are studied. • Closely pre-injection operations leads to increase of combustion intensity. • Early pre-injection operations leads to lower combustion intensity. • Early pre-injection modes provide better NO x emission. - Abstract: Pre-injection strategy is considered to be one of the most important ways to improve diesel engine performance, emission and combustion. It is the same important factor in pilot diesel compression ignition natural gas (CING) engine. In this study, effects of pre-injection timing on combustion and emission performances were experimentally studied in a CING engine which was modified from a turbocharged six-cylinder diesel engine. The experiments were conducted at constant speed of 1400 rpm and different engine loads with a constant fuel injection pressure of 1100 bar. Main injection timing was fixed at 10 °CA BTDC in the advance process of pre-injection timing. The cylinder pressure, heart release rate (HRR), pressure rise rate (PRR), start of combustion (SOC) and coefficient of variation (COV IMEP ), as well as NO x , HC and CO emissions were analyzed. The results indicated that closely pre-injection operations lead to the advance of SOC which intensified combustion of in-cylinder mixture, thereby resulting in higher cylinder pressure, HRR and PRR, as well higher NO x emissions and lower HC and CO emissions. However, early pre-injection operations lead to lower cylinder pressure, HRR and PRR due to decreasing in combustion intensity. Pre-injection timing of 70 °CA BTDC is a conversion point in which influence of pre-injection fuel on ignition and combustion of natural gas nearly disappeared and lowest NO x emission could be obtained. Compared with single injection ignition mode, NO x emissions at the conversion point were reduced by 33%, 38% and 7% at engine load of 38%, 60% and 80% respectively. This is important for the conditions that ignition fuel

Dynamic ignition regime of condensed system by radiate heat flux

International Nuclear Information System (INIS)

Arkhipov, V A; Zolotorev, N N; Korotkikh, A G; Kuznetsov, V T

2017-01-01

The main ignition characteristics of high-energy materials are the ignition time and critical heat flux allowing evaluation of the critical conditions for ignition, fire and explosive safety for the test solid propellants. The ignition process is typically studied in stationary conditions of heat input at constant temperature of the heating surface, environment or the radiate heat flux on the sample surface. In real conditions, ignition is usually effected at variable time-dependent values of the heat flux. In this case, the heated layer is formed on the sample surface in dynamic conditions and significantly depends on the heat flux change, i.e. increasing or decreasing falling heat flux in the reaction period of the propellant sample. This paper presents a method for measuring the ignition characteristics of a high-energy material sample in initiation of the dynamic radiant heat flux, which includes the measurement of the ignition time when exposed to a sample time varying radiant heat flux given intensity. In case of pyroxyline containing 1 wt. % of soot, it is shown that the ignition times are reduced by 20–50 % depending on the initial value of the radiant flux density in initiation by increasing or decreasing radiant heat flux compared with the stationary conditions of heat supply in the same ambient conditions. (paper)

Effect of advanced injection timing on the performance of rapeseed oil in diesel engines

International Nuclear Information System (INIS)

Nwafor, O.M.I.; Rice, G.; Ogbonna, A.I.

2000-01-01

Combustion studies on both diesel fuel and vegetable oil fuels, with the standard and advanced injection timing, were carried out using the same engine and test procedures so that comparative assessments may be made. The diesel engine principle demands self-ignition of the fuel as it is injected at some degrees before top dead centre (BTDC) into the hot compressed cylinder gas. Longer delays between injection and ignition lead to unacceptable rates of pressure rise with the result of diesel knock because too much fuel is ready to take part in premixed combustion. Alternative fuels have been noted to exhibit longer delay periods and slower burning rate especially at low load operating conditions hence resulting in late combustion in the expansion stroke. Advanced injection timing is expected to compensate these effects. The engine has standard injection timing of 30degC BTDC. The injection was first advanced by 5.5degC given injection timing of 35.5degC BTDC. The engine performance was very erratic on this timing. The injection was then advanced by 3.5degC and the effects are presented in this paper. The engine performance was smooth especially at low load levels. The ignition delay was reduced through advanced injection but tended to incur a slight increase in fuel consumption. Moderate advanced injection timing is recommended for low speed operations. (Author)

Travelling wave solutions for some time-delayed equations through factorizations

International Nuclear Information System (INIS)

Fahmy, E.S.

2008-01-01

In this work, we use factorization method to find explicit particular travelling wave solutions for the following important nonlinear second-order partial differential equations: The generalized time-delayed Burgers-Huxley, time-delayed convective Fishers, and the generalized time-delayed Burgers-Fisher. Using the particular solutions for these equations we find the general solutions, two-parameter solution, as special cases

Finite-time stability of neutral-type neural networks with random time-varying delays

Science.gov (United States)

Ali, M. Syed; Saravanan, S.; Zhu, Quanxin

2017-11-01

This paper is devoted to the finite-time stability analysis of neutral-type neural networks with random time-varying delays. The randomly time-varying delays are characterised by Bernoulli stochastic variable. This result can be extended to analysis and design for neutral-type neural networks with random time-varying delays. On the basis of this paper, we constructed suitable Lyapunov-Krasovskii functional together and established a set of sufficient linear matrix inequalities approach to guarantee the finite-time stability of the system concerned. By employing the Jensen's inequality, free-weighting matrix method and Wirtinger's double integral inequality, the proposed conditions are derived and two numerical examples are addressed for the effectiveness of the developed techniques.

Heterogeneity of time delays determines synchronization of coupled oscillators.

Science.gov (United States)

Petkoski, Spase; Spiegler, Andreas; Proix, Timothée; Aram, Parham; Temprado, Jean-Jacques; Jirsa, Viktor K

2016-07-01

Network couplings of oscillatory large-scale systems, such as the brain, have a space-time structure composed of connection strengths and signal transmission delays. We provide a theoretical framework, which allows treating the spatial distribution of time delays with regard to synchronization, by decomposing it into patterns and therefore reducing the stability analysis into the tractable problem of a finite set of delay-coupled differential equations. We analyze delay-structured networks of phase oscillators and we find that, depending on the heterogeneity of the delays, the oscillators group in phase-shifted, anti-phase, steady, and non-stationary clusters, and analytically compute their stability boundaries. These results find direct application in the study of brain oscillations.

Effect of oxygen content on n-heptane auto-ignition characteristics in a HCCI engine

International Nuclear Information System (INIS)

Wu, Zhijun; Kang, Zhe; Deng, Jun; Hu, Zongjie; Li, Liguang

2016-01-01

Highlights: • n-Heptane HCCI combustion under air and oxygen intake was compared. • n-Heptane auto-ignition postponed due to higher specific heat capacity as oxygen increase. • The increment of heat release fraction during low temperature reaction is studied. • Oxygen enrichment lead to suppressed negative temperature coefficient. • The mechanism of low temperature reaction enhancement as oxygen increase is investigated. - Abstract: To take maximum advantage of the high efficiency of homogeneous charge compression ignition combustion mode and internal combustion Rankine cycle concept, in this study, the n-heptane auto-ignition characteristics have been investigated using a compression ignition internal combustion Rankine cycle engine test bench and a zero-dimensional thermodynamic model coupled with a detailed kinetic model. The n-heptane auto-ignition process shows that under both air and oxygen intake, a typical two-stage combustion in which oxygen enrichment has very minor effects on the n-heptane high temperature reaction. The higher specific heat capacity of oxygen compared with nitrogen leads to an overall increased specific heat capacity, which lowers the in-cylinder temperature during compression stroke, thereby delaying the low temperature reaction initial timing. The higher oxygen content also improves the H-atom abstraction, first O_2 addition, second O_2 addition and peroxyalkylhydroperoxide isomerization, thereby improving the overall reaction rate and the heat release fraction of low temperature reaction. As a result, the in-cylinder temperature at the end of low temperature reaction also increases, thereby shortening significantly the negative temperature coefficient duration compared with a combustion cycle using air as oxidizer.

STUDENT AWARD FINALIST: Oxygen Pathways in Streamer Discharge for Transient Plasma Ignition

Science.gov (United States)

Pendleton, S. J.; Bowman, S.; Singleton, D.; Watrous, J.; Carter, C.; Lempert, W.; Gundersen, M. A.

2011-10-01

The use of streamers for the ignition of fuels, also known as transient plasma ignition (TPI), has been shown in a variety of engines to improve combustion through decreased ignition delay, increased lean burn capability and increased energy release relative to conventional spark ignition. The mechanisms behind these improvements, however, remain poorly understood. Temperature measurements by optical emission spectroscopy demonstrate that ignition by TPI is a nonthermal process, and thus is almost entirely dependent on the production and presence of electron impact-created active species in the discharge afterglow. Of particular interest are active oxygen species due to their relatively long lifetimes at high pressures and the pivotal role they play in combustion reactions. In order to elucidate the oxygen pathways, here we report the investigation of the temporal evolution of the populations of atomic oxygen and ozone by use of two-photon absorption laser induced fluorescence (TALIF) and UV absorption, respectively. Experimental results are presented and compared to kinetic modeling of the streamers. Future experiments are proposed to better understand the physics behind TPI. Supported by NSF, AFOSR, NumerEx-ONR, AFRL-WPAFB.

Thermal ignition revisited with two-dimensional molecular dynamics: role of fluctuations in activated collisions

OpenAIRE

Sirmas, Nick; Radulescu, Matei I.

2016-01-01

The problem of thermal ignition in a homogeneous gas is revisited from a molecular dynamics perspective. A two-dimensional model is adopted, which assumes reactive disks of type A and B in a fixed area that react to form type C products if an activation threshold for impact is surpassed. Such a reaction liberates kinetic energy to the product particles, representative of the heat release. The results for the ignition delay are compared with those obtained from the continuum description assumi...

Adaptive modification of the delayed feedback control algorithm with a continuously varying time delay

International Nuclear Information System (INIS)

Pyragas, V.; Pyragas, K.

2011-01-01

We propose a simple adaptive delayed feedback control algorithm for stabilization of unstable periodic orbits with unknown periods. The state dependent time delay is varied continuously towards the period of controlled orbit according to a gradient-descent method realized through three simple ordinary differential equations. We demonstrate the efficiency of the algorithm with the Roessler and Mackey-Glass chaotic systems. The stability of the controlled orbits is proven by computation of the Lyapunov exponents of linearized equations. -- Highlights: → A simple adaptive modification of the delayed feedback control algorithm is proposed. → It enables the control of unstable periodic orbits with unknown periods. → The delay time is varied continuously according to a gradient descend method. → The algorithm is embodied by three simple ordinary differential equations. → The validity of the algorithm is proven by computation of the Lyapunov exponents.

Stability analysis of linear switching systems with time delays

International Nuclear Information System (INIS)

Li Ping; Zhong Shouming; Cui Jinzhong

2009-01-01

The issue of stability analysis of linear switching system with discrete and distributed time delays is studied in this paper. An appropriate switching rule is applied to guarantee the stability of the whole switching system. Our results use a Riccati-type Lyapunov functional under a condition on the time delay. So, switching systems with mixed delays are developed. A numerical example is given to illustrate the effectiveness of our results.

Time to ignition is influenced by both moisture content and soluble carbohydrates in live Douglas fir and Lodgepole pine needles

Science.gov (United States)

Matt Jolly; Sara McAllister; Mark Finney; Ann Hadlow

2010-01-01

Living plants are often the primary fuels burning in wildland fire but little is known about the factors that govern their ignition behavior. Moisture content has long been hypothesized to determine the characteristics of fires spreading in live fuels but moisture content alone fails to explain observed differences in the ignition of various species at different times...

Modelling biochemical networks with intrinsic time delays: a hybrid semi-parametric approach

Directory of Open Access Journals (Sweden)

Oliveira Rui

2010-09-01

Full Text Available Abstract Background This paper presents a method for modelling dynamical biochemical networks with intrinsic time delays. Since the fundamental mechanisms leading to such delays are many times unknown, non conventional modelling approaches become necessary. Herein, a hybrid semi-parametric identification methodology is proposed in which discrete time series are incorporated into fundamental material balance models. This integration results in hybrid delay differential equations which can be applied to identify unknown cellular dynamics. Results The proposed hybrid modelling methodology was evaluated using two case studies. The first of these deals with dynamic modelling of transcriptional factor A in mammalian cells. The protein transport from the cytosol to the nucleus introduced a delay that was accounted for by discrete time series formulation. The second case study focused on a simple network with distributed time delays that demonstrated that the discrete time delay formalism has broad applicability to both discrete and distributed delay problems. Conclusions Significantly better prediction qualities of the novel hybrid model were obtained when compared to dynamical structures without time delays, being the more distinctive the more significant the underlying system delay is. The identification of the system delays by studies of different discrete modelling delays was enabled by the proposed structure. Further, it was shown that the hybrid discrete delay methodology is not limited to discrete delay systems. The proposed method is a powerful tool to identify time delays in ill-defined biochemical networks.

Anticontrol of chaos in continuous-time systems via time-delay feedback.

Science.gov (United States)

Wang, Xiao Fan; Chen, Guanrong; Yu, Xinghuo

2000-12-01

In this paper, a systematic design approach based on time-delay feedback is developed for anticontrol of chaos in a continuous-time system. This anticontrol method can drive a finite-dimensional, continuous-time, autonomous system from nonchaotic to chaotic, and can also enhance the existing chaos of an originally chaotic system. Asymptotic analysis is used to establish an approximate relationship between a time-delay differential equation and a discrete map. Anticontrol of chaos is then accomplished based on this relationship and the differential-geometry control theory. Several examples are given to verify the effectiveness of the methodology and to illustrate the systematic design procedure. (c) 2000 American Institute of Physics.

A continuous time Cournot duopoly with delays

International Nuclear Information System (INIS)

Gori, Luca; Guerrini, Luca; Sodini, Mauro

2015-01-01

This paper extends the classical repeated duopoly model with quantity-setting firms of Bischi et al. (1998) by assuming that production of goods is subject to some gestation lags but exchanges take place continuously in the market. The model is expressed in the form of differential equations with discrete delays. By using some recent mathematical techniques and numerical experiments, results show some dynamic phenomena that cannot be observed when delays are absent. In addition, depending on the extent of time delays and inertia, synchronisation failure can arise even in the event of homogeneous firms.

Delay time in a single barrier for a movable quantum shutter

International Nuclear Information System (INIS)

Hernandez, Alberto

2010-01-01

The transient solution and delay time for a δ potential scatterer with a movable quantum shutter is calculated by solving analytically the time-dependent Schroedinger equation. The delay time is analyzed as a function of the distance between the shutter and the potential barrier and also as a function of the distance between the potential barrier and the detector. In both cases, it is found that the delay time exhibits a dynamical behavior and that it tends to a saturation value Δt sat in the limit of very short distances, which represents the maximum delay produced by the potential barrier near the interaction region. The phase time τ θ , on the other hand, is not an appropriate time scale for measuring the time delay near the interaction region, except if the shutter is moved far away from the potential. The role played by the antibound state of the system on the behavior of the delay time is also discussed.

Super-transient scaling in time-delay autonomous Boolean network motifs

Energy Technology Data Exchange (ETDEWEB)

D' Huys, Otti, E-mail: otti.dhuys@phy.duke.edu; Haynes, Nicholas D. [Department of Physics, Duke University, Durham, North Carolina 27708 (United States); Lohmann, Johannes [Department of Physics, Duke University, Durham, North Carolina 27708 (United States); Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin (Germany); Gauthier, Daniel J. [Department of Physics, Duke University, Durham, North Carolina 27708 (United States); Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)

2016-09-15

Autonomous Boolean networks are commonly used to model the dynamics of gene regulatory networks and allow for the prediction of stable dynamical attractors. However, most models do not account for time delays along the network links and noise, which are crucial features of real biological systems. Concentrating on two paradigmatic motifs, the toggle switch and the repressilator, we develop an experimental testbed that explicitly includes both inter-node time delays and noise using digital logic elements on field-programmable gate arrays. We observe transients that last millions to billions of characteristic time scales and scale exponentially with the amount of time delays between nodes, a phenomenon known as super-transient scaling. We develop a hybrid model that includes time delays along network links and allows for stochastic variation in the delays. Using this model, we explain the observed super-transient scaling of both motifs and recreate the experimentally measured transient distributions.

Development of a pre-ignition submodel for hydrogen engines

Energy Technology Data Exchange (ETDEWEB)

Al-Baghdadi, Sadiq [University of Babylon (Iraq). Dept. of Mechanical Engineering

2005-10-15

In hydrogen-fuelled spark ignition engine applications, the onset of pre-ignition remains one of the prime limitations that needs to be addressed to avoid its incidence and achieve superior performance. This paper describes a new pre-ignition submodel for engine modelling codes. The effects of changes in key operating variables, such as compression ratio, spark timing, intake pressure, and temperature on pre-ignition limiting equivalence ratios are established both analytically and experimentally. With the established pre-ignition model, it is possible not only to investigate whether pre-ignition is observed with changing operating and design parameters, but also to evaluate those parameters' effects on the maximum possible pre-ignition intensity. (author)

Advances in shock timing experiments on the National Ignition Facility

International Nuclear Information System (INIS)

Robey, H F; Celliers, P M; Moody, J D; Sater, J; Parham, T; Kozioziemski, B; Dylla- Spears, R; Ross, J S; LePape, S; Ralph, J E; Hohenberger, M; Dewald, E L; Berzak Hopkins, L; Kroll, J J; Yoxall, B E; Hamza, A V; Landen, O L; Edwards, M J; Boehly, T R; Nikroo, A

2016-01-01

Recent advances in shock timing experiments and analysis techniques now enable shock measurements to be performed in cryogenic deuterium-tritium (DT) ice layered capsule implosions on the National Ignition Facility (NIF). Previous measurements of shock timing in inertial confinement fusion (ICF) implosions were performed in surrogate targets, where the solid DT ice shell and central DT gas were replaced with a continuous liquid deuterium (D2) fill. These previous experiments pose two surrogacy issues: a material surrogacy due to the difference of species (D2 vs. DT) and densities of the materials used and a geometric surrogacy due to presence of an additional interface (ice/gas) previously absent in the liquid-filled targets. This report presents experimental data and a new analysis method for validating the assumptions underlying this surrogate technique. (paper)

Advances in shock timing experiments on the National Ignition Facility

Science.gov (United States)

Robey, H. F.; Celliers, P. M.; Moody, J. D.; Sater, J.; Parham, T.; Kozioziemski, B.; Dylla-Spears, R.; Ross, J. S.; LePape, S.; Ralph, J. E.; Hohenberger, M.; Dewald, E. L.; Berzak Hopkins, L.; Kroll, J. J.; Yoxall, B. E.; Hamza, A. V.; Boehly, T. R.; Nikroo, A.; Landen, O. L.; Edwards, M. J.

2016-03-01

Recent advances in shock timing experiments and analysis techniques now enable shock measurements to be performed in cryogenic deuterium-tritium (DT) ice layered capsule implosions on the National Ignition Facility (NIF). Previous measurements of shock timing in inertial confinement fusion (ICF) implosions were performed in surrogate targets, where the solid DT ice shell and central DT gas were replaced with a continuous liquid deuterium (D2) fill. These previous experiments pose two surrogacy issues: a material surrogacy due to the difference of species (D2 vs. DT) and densities of the materials used and a geometric surrogacy due to presence of an additional interface (ice/gas) previously absent in the liquid-filled targets. This report presents experimental data and a new analysis method for validating the assumptions underlying this surrogate technique.

Tunable delay time and Hartman effect in graphene magnetic barriers

International Nuclear Information System (INIS)

Ban, Yue; Wang, Lin-Jun; Chen, Xi

2015-01-01

Tunable group delay and Hartman effect have been investigated for massless Dirac electrons in graphene magnetic barriers. In the presence of magnetic field, dwell time is found to be equal to net group delay plus the group delay contributing from the lateral shifts. The group delay times are discussed in both cases of normal and oblique incidence, to clarify the nature of Hartman effect. In addition, the group delay in transmission can be modulated from subluminality to superluminality by adjusting the magnetic field, which may also lead to potential applications in graphene-based microelectronics

Study of calculated and measured time dependent delayed neutron yields

International Nuclear Information System (INIS)

Waldo, R.W.

1980-05-01

Time-dependent delayed neutron emission is of interest in reactor design, reactor dynamics, and nuclear physics studies. The delayed neutrons from neutron-induced fission of 232 U, 237 Np, 238 Pu, 241 Am, /sup 242m/Am, 245 Cm, and 249 Cf were studied for the first time. The delayed neutron emission from 232 Th, 233 U, 235 U, 238 U, 239 Pu, 241 Pu, and 242 Pu were measured as well. The data were used to develop an empirical expression for the total delayed neutron yield. The expression gives accurate results for a large variety of nuclides from 232 Th to 252 Cf. The data measuring the decay of delayed neutrons with time were used to derive another empirical expression predicting the delayed neutron emission with time. It was found that nuclides with similar mass-to-charge ratios have similar decay patterns. Thus the relative decay pattern of one nuclide can be established by any measured nuclide with a similar mass-to-charge ratio. A simple fission product yield model was developed and applied to delayed neutron precursors. It accurately predicts observed yield and decay characteristics. In conclusion, it is possible to not only estimate the total delayed neutron yield for a given nuclide but the time-dependent nature of the delayed neutrons as well. Reactors utilizing recycled fuel or burning actinides are likely to have inventories of fissioning nuclides that have not been studied until now. The delayed neutrons from these nuclides can now be incorporated so that their influence on the stability and control of reactors can be delineated. 8 figures, 39 tables

Lag synchronization of chaotic systems with time-delayed linear

Indian Academy of Sciences (India)

In this paper, the lag synchronization of chaotic systems with time-delayed linear terms via impulsive control is investigated. Based on the stability theory of impulsive delayed differential equations, some sufficient conditions are obtained guaranteeing the synchronized behaviours between two delayed chaotic systems.

Ignition experiment in a single-turn-coil tokamak

International Nuclear Information System (INIS)

Carrera, R.; Driga, M.; Gully, J.H.

1989-01-01

A novel concept for a fusion ignition experiment, IGNITEX proposed along the lines of previous ideas for a compact thermonuclear device is analyzed. A single-turn-coil tokamak is analyzed. A single-turn-coil tokamak supplied by homopolar generators can ohmically heat a DT plasma to ignition conditions and maintain a thermally stable ignited phase for about ten energy confinement times. The IGNITEX experiment can provide a simple and relatively inexpensive way to produce and control ignited plasmas for scientific study

Definition of Time Induction of Self-Ignition of the Substance on the Prognostic Extrapolation Depending on the Basis of Indicators Fire and Explosion Hazard

International Nuclear Information System (INIS)

Sechin, A; Kyrmakova, O; Osipenko, S

2016-01-01

In this article the research directed on development of a technique of definition of time of induction of the self-ignition of substances and materials which is an indicator of the beginning of development of an emergency is conducted. The experiment consisting in supervision over process of self-ignition of coal and oil deposits was the basis for research. On the basis of experimental data the curve expressing analytic - expected dependence of size of temperature of ignition on induction time was constructed. Proceeding from graphical representation of process, functional dependence of time of induction on a temperature indicator was received: y = 16920 • x 0 537 . By means of known indicators of such substances as bitumen oil oxidized (the combustible solid substance received by oxidation of residual product of oil refining) and tar oil (the combustible solid substance which is residual product of oil refining) and the received algorithm, verification of reliability of the received dependence and a technique of definition of time of induction of spontaneous ignition of deposits of oil in general was carried out. The practical importance of the conducted research is that having data on time of induction of process of self-ignition, by means of preventive measures becomes possible to avoid and prevent accidents in oil and oil processing branches, at the same time loss of property and loss of human life. (paper)

Effect of Timing and Location of Hotspot on Super Knock during Pre-ignition

KAUST Repository

Jaasim, Mohammed; Hernandez Perez, Francisco; Vedharaj, S.; Vallinayagam, R.; Dibble, Robert W.; Im, Hong G.

2017-01-01

Pre-ignition in SI engine is a critical issue that needs addressing as it may lead to super knock event. It is widely accepted that pre-ignition event emanates from hot spot(s) that can be anywhere inside the combustion chamber. The location

Evaporation and Ignition Characteristics of Water Emulsified Diesel under Conventional and Low Temperature Combustion Conditions

Directory of Open Access Journals (Sweden)

Zhaowen Wang

2017-07-01

Full Text Available The combination of emulsified diesel and low temperature combustion (LTC technology has great potential in reducing engine emissions. A visualization study on the spray and combustion characteristics of water emulsified diesel was conducted experimentally in a constant volume chamber under conventional and LTC conditions. The effects of ambient temperature on the evaporation, ignition and combustion characteristics of water emulsified diesel were studied under cold, evaporating and combustion conditions. Experimental results showed that the ambient temperature had little effect on the spray structures, in terms of the liquid core length, the spray shape and the spray area. However, higher ambient temperature slightly reduced the Sauter Mean Diameter (SMD of the spray droplets. The auto-ignition delay time increased significantly with the decrease of the ambient temperature. The ignition process always occurred at the entrainment region near the front periphery of the liquid core. This entrainment region was evolved from the early injected fuel droplets which were heated and mixed by the continuous entrainment until the local temperature and equivalence ratio reached the ignition condition. The maximum value of integrated natural flame luminosity (INFL reduced by 60% when the ambient temperature dropped from 1000 to 800 K, indicating a significant decrease of the soot emissions could be achieved by LTC combustion mode than the conventional diesel engines.

Ignition of Cellulosic Paper at Low Radiant Fluxes

Science.gov (United States)

White, K. Alan

1996-01-01

The ignition of cellulosic paper by low level thermal radiation is investigated. Past work on radiative ignition of paper is briefly reviewed. No experimental study has been reported for radiative ignition of paper at irradiances below 10 Watts/sq.cm. An experimental study of radiative ignition of paper at these low irradiances is reported. Experimental parameters investigated and discussed include radiant power levels incident on the sample, the method of applying the radiation (focussed vs. diffuse Gaussian source), the presence and relative position of a separate pilot ignition source, and the effects of natural convection (buoyancy) on the ignition process in a normal gravity environment. It is observed that the incident radiative flux (in W/sq.cm) has the greatest influence on ignition time. For a given flux level, a focussed Gaussian source is found to be advantageous to a more diffuse, lower amplitude, thermal source. The precise positioning of a pilot igniter relative to gravity and to the fuel sample affects the ignition process, but the precise effects are not fully understood. Ignition was more readily achieved and sustained with a horizontal fuel sample, indicating the buoyancy plays a role in the ignition process of cellulosic paper. Smoldering combustion of doped paper samples was briefly investigated, and results are discussed.

Synchronization of time-delayed systems with chaotic modulation and cryptography

International Nuclear Information System (INIS)

Banerjee, Santo

2009-01-01

This paper presents a method of synchronization between two time-delayed systems where the delay times are modulated by a common chaotic signal of the driving system. The technique is well applied to two identical autonomous continuous-time-delayed systems with numerical simulations. Finally, a new method of encryption is generated for digital messages. This method is illustrated with two different encryption processes for text as well as picture messages.

Progress in the indirect-drive National Ignition Campaign

International Nuclear Information System (INIS)

Landen, O L; Benedetti, R; Bleuel, D; Bradley, D K; Caggiano, J A; Callahan, D A; Celliers, P M; Cerjan, C J; Clark, D; Collins, G W; Dewald, E L; Dixit, S N; Doeppner, T; Eggert, J; Farley, D; Glenn, S M; Boehly, T R; Edgell, D; Glebov, V; Frenje, J A

2012-01-01

We have carried out precision optimization of inertial confinement fusion ignition scale implosions. We have achieved hohlraum temperatures in excess of the 300 eV ignition goal with hot-spot symmetry and shock timing near ignition specs. Using slower rise pulses to peak power and extended pulses resulted in lower hot-spot adiabat and higher main fuel areal density at about 80% of the ignition goal. Yields are within a factor of 5–6 of that required to initiate alpha dominated burn. It is likely we will require thicker shells (+15–20%) to reach ignition velocity without mixing of ablator material into the hot spot. (paper)

Heating and ignition of small wood cylinders

Science.gov (United States)

Wallace L. Fons

1950-01-01

The literature provides limited information on the time of ignition of wood under conditions of rapid heating such as occur in forest and structure fires. An investigation was made of ease of ignition as affected by such physical properties of wood as initial temperature, size, and moisture content and by temperature of ambient gas or rate of heating. Temperature-time...

Ignition and Inertial Confinement Fusion at The National Ignition Facility

International Nuclear Information System (INIS)

Moses, E.

2009-01-01

The National Ignition Facility (NIF), the world's largest and most powerful laser system for inertial confinement fusion (ICF) and for studying high-energy-density (HED) science, is now operational at Lawrence Livermore National Laboratory (LLNL). The NIF is now conducting experiments to commission the laser drive, the hohlraum and the capsule and to develop the infrastructure needed to begin the first ignition experiments in FY 2010. Demonstration of ignition and thermonuclear burn in the laboratory is a major NIF goal. NIF will achieve this by concentrating the energy from the 192 beams into a mm 3 -sized target and igniting a deuterium-tritium mix, liberating more energy than is required to initiate the fusion reaction. NIF's ignition program is a national effort managed via the National Ignition Campaign (NIC). The NIC has two major goals: execution of DT ignition experiments starting in FY2010 with the goal of demonstrating ignition and a reliable, repeatable ignition platform by the conclusion of the NIC at the end of FY2012. The NIC will also develop the infrastructure and the processes required to operate NIF as a national user facility. The achievement of ignition at NIF will demonstrate the scientific feasibility of ICF and focus worldwide attention on laser fusion as a viable energy option. A laser fusion-based energy concept that builds on NIF, known as LIFE (Laser Inertial Fusion Energy), is currently under development. LIFE is inherently safe and can provide a global carbon-free energy generation solution in the 21st century. This paper describes recent progress on NIF, NIC, and the LIFE concept.

Time-delay interferometric ranging for space-borne gravitational-wave detectors

International Nuclear Information System (INIS)

Tinto, Massimo; Vallisneri, Michele; Armstrong, J.W.

2005-01-01

Space-borne interferometric gravitational-wave detectors, sensitive in the low-frequency (mHz) band, will fly in the next decade. In these detectors, the spacecraft-to-spacecraft light-travel times will necessarily be unequal and time varying, and (because of aberration) will have different values on up- and down-links. In such unequal-armlength interferometers, laser-phase noise will be canceled by taking linear combinations of the laser-phase observables measured between pairs of spacecraft, appropriately time shifted by the light propagation times along the corresponding arms. This procedure, known as time-delay interferometry (TDI), requires an accurate knowledge of the light-time delays as functions of time. Here we propose a high-accuracy technique to estimate these time delays, and we study its use in the context of the Laser Interferometer Space Antenna (LISA) mission. We refer to this ranging technique, which relies on the TDI combinations themselves, as time-delay interferometric ranging (TDIR). For every TDI combination, we show that, by minimizing the rms power in that combination (averaged over integration times ∼10 4 s) with respect to the time-delay parameters, we obtain estimates of the time delays accurate enough to cancel laser noise to a level well below the secondary noises. Thus TDIR allows the implementation of TDI without the use of dedicated interspacecraft ranging systems, with a potential simplification of the LISA design. In this paper we define the TDIR procedure formally, and we characterize its expected performance via simulations with the Synthetic LISA software package

Goodwin accelerator model revisited with fixed time delays

Science.gov (United States)

Matsumoto, Akio; Merlone, Ugo; Szidarovszky, Ferenc

2018-05-01

Dynamics of Goodwin's accelerator business cycle model is reconsidered. The model is characterized by a nonlinear accelerator and an investment time delay. The role of the nonlinearity for the birth of persistent oscillations is fully discussed in the existing literature. On the other hand, not much of the role of the delay has yet been revealed. The purpose of this paper is to show that the delay really matters. In the original framework of Goodwin [6], it is first demonstrated that there is a threshold value of the delay: limit cycles arise for smaller values than the threshold and so do sawtooth oscillations for larger values. In the extended framework in which a consumption or saving delay, in addition to the investment delay, is introduced, three main results are demonstrated under assumption of the identical length of investment and consumption delays. The dynamics with consumption delay is basically the same as that of the single delay model. Second, in the case of saving delay, the steady state can coexist with the stable and unstable limit cycles in the stable case. Third, in the unstable case, there is an interval of delay in which the limit cycle or the sawtooth oscillation emerges depending on the choice of the constant initial function.

The individual effects of cetane number, oxygen content or fuel properties on the ignition delay, combustion characteristics, and cyclic variation of a turbocharged CRDI diesel engine – Part 1

International Nuclear Information System (INIS)

Labeckas, Gvidonas; Slavinskas, Stasys; Kanapkienė, Irena

2017-01-01

Highlights: • Diesel-HRD fuel blends involving ethanol (E) or biodiesel (B) were investigated in a turbocharged CRDI engine. • Improved cetane number of fuel blends ambiguously affected the ignition delay and maximum heat release rate. • Increased fuel-bound oxygen content enhanced combustion, heat release and in-cylinder pressure at 2500 rpm. • Fuel properties almost did not change premixed phase, but affected burn angle MBF 50 and the end of combustion. • Burn angles MBF 50 and MBF 90 were 1.0° and 5.7° CADs shorter when using oxygenated blend OE4 (3.6 wt%) at 2000 rpm. - Abstract: The study deals with the effects made by individual variation of cetane number, fuel-oxygen content, or widely differing properties of diesel-HRD fuel blends involving ethanol (E) or biodiesel (B) on the ignition delay, combustion phenomenon, maximum heat release rate, and the cyclic variation of a turbocharged CRDI diesel engine. The most important control factors one after another operated separately in this study to make a difference. Load characteristics were taken when running with a straight diesel and various (18) diesel-HRD fuel blends at maximum torque mode of 2000 rpm and speeds of 1500 and 2500 rpm to provide correct interpretation of the test results. Then, load (bmep) characteristics were plotted as a function of the relative air-fuel ratio (λ) and the analysis of combustion parameters was conducted for the ‘lambda’ values of λ = 1.30, 1.25 and 1.20, at the respective speeds of 1500, 2000 and 2500 rpm. Analysis of changes in the ignition delay, combustion characteristics, and the cyclic variation of parameters when using fuel blends of both origins was performed on comparative bases with the corresponding values measured with ‘base-line’ blends with CN = 51.2 or zero oxygen content and a straight diesel to reveal the potential developing trends. The enhanced cetane number of oxygenated fuels improved combustion and reduced cyclic variation when

Another definition for time delay

International Nuclear Information System (INIS)

Narnhofer, H.

1980-01-01

Time delay is defined by geometrical considerations which work in classical as well as in quantum mechanics, and its connection with the S-matrix and the virial is proven for potentials with V(x vector) and x vector V(x vector) vanishing as rsup(-1-epsilon) for r -> infinity. (Author)

Recent progress in ignition fusion research on the National Ignition Facility

International Nuclear Information System (INIS)

Leeper, Ramon J.

2011-01-01

This paper will review the ignition fusion research program that is currently being carried out on the National Ignition Facility (NIF) located at Lawrence Livermore National Laboratory. This work is being conducted under the auspices of the National Ignition Campaign (NIC) that is a broad collaboration of national laboratories and universities that together have developed a detailed research plan whose goal is ignition in the laboratory. The paper will begin with a description of the NIF facility and associated experimental facilities. The paper will then focus on the ignition target and hohlraum designs that will be tested in the first ignition attempts on NIF. The next topic to be introduced will be a description of the diagnostic suite that has been developed for the initial ignition experiments on NIF. The paper will then describe the experimental results that were obtained in experiments conducted during the fall of 2009 on NIF. Finally, the paper will end with a description of the detailed experimental plans that have been developed for the first ignition campaign that will begin later this year. (author)

On the linearity of cross-correlation delay times

Science.gov (United States)

Mercerat, E. D.; Nolet, G.

2012-12-01

We investigate the question whether a P-wave delay time Δ T estimated by locating the maximum of the cross-correlation function between data d(t) and a predicted test function s(t): γ (t) = ∫ t1t_2 s(τ ) d(τ -t) \\ {d}τ, provides an estimate of the Delta T that is (quasi-)linear with the relative velocity perturbation deltaln V_P}. Such linearity is intuitive if the data d(t) is an undeformed but delayed replica of the test signal, i.e. if d(t)=s(t-Delta T). Then the maximum of gamma (t) is shifted exactly by the delay Delta T, and linearity holds even for Delta T very large. In this case, we say that the body waves are in the ray theoretical regime and their delays, because of Fermat's Principle, depend quasi-linearly on the relative velocity (or slowness) perturbations deltaln V_P in the model. However, even if we correct for dispersion induced by the instrument response and by attenuation, body waves may show frequency dependent delay times that are caused by diffraction effects around lateral heterogeneities. It is not a-priori clear that linearity holds for Delta T, as is assumed in finite-frequency theory, if the waveforms of d(t) and s(t) differ substantially because of such dispersion. To test the linearity, we generate synthetic seismograms between two boreholes, and between the boreholes and the surface, in a 3D box of 200 × 120 × 120 m. The heterogeneity is a checkerboard with cubic anomalies of size 12 × 12 × 12 m. We test two different anomaly amplitudes: ± 2% and ± 5%, and measure Delta T using a test seismogram s(t) computed for an homogeneous medium. We also predict the delays for the 5% model from those in the 2% model by multiplying with 5/2. These predictions are in error by 10-20% of the delay, which is usually acceptable for tomography when compared with actual data errors. A slight bias in the prediction indicates that the Wielandt effect - the fact that negative delays suffer less wavefront healing than positive delays - is a

Advanced ignition for automotive engines

OpenAIRE

Pineda, Daniel Ivan

2017-01-01

Spark plugs have been igniting combustible mixtures like those found in automotive engines for over a century, and the principles of the associated ignition techniques using thermal plasma (inductive or capacitive sparks) have remained relatively unchanged during that time. However, internal combustion engines are increasingly operating with boosted intake pressures (i.e. turbo- or super-charged) in order to maintain power output while simultaneously reducing engine size and weight, and they ...

Finite-Time Attractivity for Diagonally Dominant Systems with Off-Diagonal Delays

Directory of Open Access Journals (Sweden)

T. S. Doan

2012-01-01

Full Text Available We introduce a notion of attractivity for delay equations which are defined on bounded time intervals. Our main result shows that linear delay equations are finite-time attractive, provided that the delay is only in the coupling terms between different components, and the system is diagonally dominant. We apply this result to a nonlinear Lotka-Volterra system and show that the delay is harmless and does not destroy finite-time attractivity.

Measurement of time delays in gated radiotherapy for realistic respiratory motions

International Nuclear Information System (INIS)

Chugh, Brige P.; Quirk, Sarah; Conroy, Leigh; Smith, Wendy L.

2014-01-01

Purpose: Gated radiotherapy is used to reduce internal motion margins, escalate target dose, and limit normal tissue dose; however, its temporal accuracy is limited. Beam-on and beam-off time delays can lead to treatment inefficiencies and/or geographic misses; therefore, AAPM Task Group 142 recommends verifying the temporal accuracy of gating systems. Many groups use sinusoidal phantom motion for this, under the tacit assumption that use of sinusoidal motion for determining time delays produces negligible error. The authors test this assumption by measuring gating time delays for several realistic motion shapes with increasing degrees of irregularity. Methods: Time delays were measured on a linear accelerator with a real-time position management system (Varian TrueBeam with RPM system version 1.7.5) for seven motion shapes: regular sinusoidal; regular realistic-shape; large (40%) and small (10%) variations in amplitude; large (40%) variations in period; small (10%) variations in both amplitude and period; and baseline drift (30%). Film streaks of radiation exposure were generated for each motion shape using a programmable motion phantom. Beam-on and beam-off time delays were determined from the difference between the expected and observed streak length. Results: For the system investigated, all sine, regular realistic-shape, and slightly irregular amplitude variation motions had beam-off and beam-on time delays within the AAPM recommended limit of less than 100 ms. In phase-based gating, even small variations in period resulted in some time delays greater than 100 ms. Considerable time delays over 1 s were observed with highly irregular motion. Conclusions: Sinusoidal motion shapes can be considered a reasonable approximation to the more complex and slightly irregular shapes of realistic motion. When using phase-based gating with predictive filters even small variations in period can result in time delays over 100 ms. Clinical use of these systems for patients

Measurement of time delays in gated radiotherapy for realistic respiratory motions

Energy Technology Data Exchange (ETDEWEB)

Chugh, Brige P.; Quirk, Sarah; Conroy, Leigh; Smith, Wendy L., E-mail: Wendy.Smith@albertahealthservices.ca [Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta T2N 4N2 (Canada)

2014-09-15

Purpose: Gated radiotherapy is used to reduce internal motion margins, escalate target dose, and limit normal tissue dose; however, its temporal accuracy is limited. Beam-on and beam-off time delays can lead to treatment inefficiencies and/or geographic misses; therefore, AAPM Task Group 142 recommends verifying the temporal accuracy of gating systems. Many groups use sinusoidal phantom motion for this, under the tacit assumption that use of sinusoidal motion for determining time delays produces negligible error. The authors test this assumption by measuring gating time delays for several realistic motion shapes with increasing degrees of irregularity. Methods: Time delays were measured on a linear accelerator with a real-time position management system (Varian TrueBeam with RPM system version 1.7.5) for seven motion shapes: regular sinusoidal; regular realistic-shape; large (40%) and small (10%) variations in amplitude; large (40%) variations in period; small (10%) variations in both amplitude and period; and baseline drift (30%). Film streaks of radiation exposure were generated for each motion shape using a programmable motion phantom. Beam-on and beam-off time delays were determined from the difference between the expected and observed streak length. Results: For the system investigated, all sine, regular realistic-shape, and slightly irregular amplitude variation motions had beam-off and beam-on time delays within the AAPM recommended limit of less than 100 ms. In phase-based gating, even small variations in period resulted in some time delays greater than 100 ms. Considerable time delays over 1 s were observed with highly irregular motion. Conclusions: Sinusoidal motion shapes can be considered a reasonable approximation to the more complex and slightly irregular shapes of realistic motion. When using phase-based gating with predictive filters even small variations in period can result in time delays over 100 ms. Clinical use of these systems for patients

Face to phase: pitfalls in time delay estimation from coherency phase

NARCIS (Netherlands)

Campfens, S.F.; van der Kooij, Herman; Schouten, Alfred Christiaan

2014-01-01

Coherency phase is often interpreted as a time delay reflecting a transmission delay between spatially separated neural populations. However, time delays estimated from corticomuscular coherency are conflicting and often shorter than expected physiologically. Recent work suggests that

A diamond detector for inertial confinement fusion X-ray bang-time measurements at the National Ignition Facility

Energy Technology Data Exchange (ETDEWEB)

MacPhee, A G; Brown, C; Burns, S; Celeste, J; Glenzer, S H; Hey, D; Jones, O S; Landen, O; Mackinnon, A J; Meezan, N; Parker, J; Edgell, D; Glebov, V Y; Kilkenny, J; Kimbrough, J

2010-11-09

An instrument has been developed to measure X-ray bang-time for inertial confinement fusion capsules; the time interval between the start of the laser pulse and peak X-ray emission from the fuel core. The instrument comprises chemical vapor deposited polycrystalline diamond photoconductive X-ray detectors with highly ordered pyrolytic graphite X-ray monochromator crystals at the input. Capsule bang-time can be measured in the presence of relatively high thermal and hard X-ray background components due to the selective band pass of the crystals combined with direct and indirect X-ray shielding of the detector elements. A five channel system is being commissioned at the National Ignition Facility at Lawrence Livermore National Laboratory for implosion optimization measurements as part of the National Ignition Campaign. Characteristics of the instrument have been measured demonstrating that X-ray bang-time can be measured with {+-} 30ps precision, characterizing the soft X-ray drive to +/- 1eV or 1.5%.

Physical characteristics of welding arc ignition process

Science.gov (United States)

Shi, Linan; Song, Yonglun; Xiao, Tianjiao; Ran, Guowei

2012-07-01

The existing research of welding arc mainly focuses on the stable combustion state and the research on the mechanism of welding arc ignition process is quite lack. The tungsten inert gas(TIG) touch arc ignition process is observed via a high speed camera and the high time resolution spectral diagnosis system. The changing phenomenon of main ionized element provided the electrons in the arc ignition is found. The metallic element is the main contributor to provide the electrons at the beginning of the discharging, and then the excitated shielding gas element replaces the function of the metallic element. The electron density during the period of the arc ignition is calculated by the Stark-broadened lines of Hα. Through the discussion with the repeatability in relaxation phenomenon, the statistical regularity in the arc ignition process is analyzed. The similar rules as above are observed through the comparison with the laser-assisted arc ignition experiments and the metal inert gas(MIG) arc ignition experiments. This research is helpful to further understanding on the generation mechanism of welding arc ignition and also has a certain academic and practical significance on enriching the welding physical theoretical foundation and improving the precise monitoring on automatic arc welding process.

Time-dependent delayed signatures from energetic photon interrogations

International Nuclear Information System (INIS)

Norman, Daren R.; Jones, James L.; Blackburn, Brandon W.; Haskell, Kevin J.; Johnson, James T.; Watson, Scott M.; Hunt, Alan W.; Spaulding, Randy; Harmon, Frank

2007-01-01

Pulsed photonuclear interrogation environments generated by 8-24 MeV electron linac are rich with time-dependent, material-specific, radiation signatures. Nitrogen-based explosives and nuclear materials can be detected by exploiting these signatures in different delayed-time regions. Numerical and experimental results presented in this paper show the unique time and energy dependence of these signatures. It is shown that appropriate delayed-time windows are essential to acquire material-specific signatures in pulsed photonuclear assessment environments. These developments demonstrate that pulsed, high-energy, photon-inspection environments can be exploited for time-dependent, material-specific signatures through the proper operation of specialized detectors and detection methods

Using Constant Time Delay to Teach Braille Word Recognition

Science.gov (United States)

Hooper, Jonathan; Ivy, Sarah; Hatton, Deborah

2014-01-01

Introduction: Constant time delay has been identified as an evidence-based practice to teach print sight words and picture recognition (Browder, Ahlbrim-Delzell, Spooner, Mims, & Baker, 2009). For the study presented here, we tested the effectiveness of constant time delay to teach new braille words. Methods: A single-subject multiple baseline…

Spark Ignition Characteristics of a L02/LCH4 Engine at Altitude Conditions

Science.gov (United States)

Kleinhenz, Julie; Sarmiento, Charles; Marshall, William

2012-01-01

The use of non-toxic propellants in future exploration vehicles would enable safer, more cost effective mission scenarios. One promising "green" alternative to existing hypergols is liquid methane/liquid oxygen. To demonstrate performance and prove feasibility of this propellant combination, a 100lbf LO2/LCH4 engine was developed and tested under the NASA Propulsion and Cryogenic Advanced Development (PCAD) project. Since high ignition energy is a perceived drawback of this propellant combination, a test program was performed to explore ignition performance and reliability versus delivered spark energy. The sensitivity of ignition to spark timing and repetition rate was also examined. Three different exciter units were used with the engine s augmented (torch) igniter. Propellant temperature was also varied within the liquid range. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks (in quiescent, room air). The escalating pressure and flow environment increases spark impedance and may at some point compromise an exciter s ability to deliver a spark. Reduced spark energies of these sparks result in more erratic ignitions and adversely affect ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1-6mJ, though multiple, similarly timed sparks of 55-75mJ were required for reliable ignition. An optimum time interval for spark application and ignition coincided with propellant introduction to the igniter and engine. Shifts of ignition timing were manifested by changes in the characteristics of the resulting ignition.

Spark Ignition Characteristics of a LO2/LCH4 Engine at Altitude Conditions

Science.gov (United States)

Kleinhenz, Julie; Sarmiento, Charles; Marshall, William

2012-01-01

The use of non-toxic propellants in future exploration vehicles would enable safer, more cost effective mission scenarios. One promising "green" alternative to existing hypergols is liquid methane/liquid oxygen. To demonstrate performance and prove feasibility of this propellant combination, a 100lbf LO2/LCH4 engine was developed and tested under the NASA Propulsion and Cryogenic Advanced Development (PCAD) project. Since high ignition energy is a perceived drawback of this propellant combination, a test program was performed to explore ignition performance and reliability versus delivered spark energy. The sensitivity of ignition to spark timing and repetition rate was also examined. Three different exciter units were used with the engine's augmented (torch) igniter. Propellant temperature was also varied within the liquid range. Captured waveforms indicated spark behavior in hot fire conditions was inconsistent compared to the well-behaved dry sparks (in quiescent, room air). The escalating pressure and flow environment increases spark impedance and may at some point compromise an exciter.s ability to deliver a spark. Reduced spark energies of these sparks result in more erratic ignitions and adversely affect ignition probability. The timing of the sparks relative to the pressure/flow conditions also impacted the probability of ignition. Sparks occurring early in the flow could trigger ignition with energies as low as 1-6mJ, though multiple, similarly timed sparks of 55-75mJ were required for reliable ignition. An optimum time interval for spark application and ignition coincided with propellant introduction to the igniter and engine. Shifts of ignition timing were manifested by changes in the characteristics of the resulting ignition.

An adaptive robust controller for time delay maglev transportation systems

Science.gov (United States)

Milani, Reza Hamidi; Zarabadipour, Hassan; Shahnazi, Reza

2012-12-01

For engineering systems, uncertainties and time delays are two important issues that must be considered in control design. Uncertainties are often encountered in various dynamical systems due to modeling errors, measurement noises, linearization and approximations. Time delays have always been among the most difficult problems encountered in process control. In practical applications of feedback control, time delay arises frequently and can severely degrade closed-loop system performance and in some cases, drives the system to instability. Therefore, stability analysis and controller synthesis for uncertain nonlinear time-delay systems are important both in theory and in practice and many analytical techniques have been developed using delay-dependent Lyapunov function. In the past decade the magnetic and levitation (maglev) transportation system as a new system with high functionality has been the focus of numerous studies. However, maglev transportation systems are highly nonlinear and thus designing controller for those are challenging. The main topic of this paper is to design an adaptive robust controller for maglev transportation systems with time-delay, parametric uncertainties and external disturbances. In this paper, an adaptive robust control (ARC) is designed for this purpose. It should be noted that the adaptive gain is derived from Lyapunov-Krasovskii synthesis method, therefore asymptotic stability is guaranteed.

Time delay of quantum scattering processes

International Nuclear Information System (INIS)

Martin, P.A.

1981-01-01

The author presents various aspects of the theory of the time delay of scattering processes. The author mainly studies non-relativistic two-body scattering processes, first summarizing briefly the theory of simple scattering systems. (Auth.)

Numerical Investigation of a Gasoline-Like Fuel in a Heavy-Duty Compression Ignition Engine Using Global Sensitivity Analysis

Energy Technology Data Exchange (ETDEWEB)

Pal, Pinaki; Probst, Daniel; Pei, Yuanjiang; Zhang, Yu; Traver, Michael; Cleary, David; Som, Sibendu

2017-03-28

Fuels in the gasoline auto-ignition range (Research Octane Number (RON) > 60) have been demonstrated to be effective alternatives to diesel fuel in compression ignition engines. Such fuels allow more time for mixing with oxygen before combustion starts, owing to longer ignition delay. Moreover, by controlling fuel injection timing, it can be ensured that the in-cylinder mixture is “premixed enough” before combustion occurs to prevent soot formation while remaining “sufficiently inhomogeneous” in order to avoid excessive heat release rates. Gasoline compression ignition (GCI) has the potential to offer diesel-like efficiency at a lower cost and can be achieved with fuels such as low-octane straight run gasoline which require significantly less processing in the refinery compared to today’s fuels. To aid the design and optimization of a compression ignition (CI) combustion system using such fuels, a global sensitivity analysis (GSA) was conducted to understand the relative influence of various design parameters on efficiency, emissions and heat release rate. The design parameters included injection strategies, exhaust gas recirculation (EGR) fraction, temperature and pressure at intake valve closure and injector configuration. These were varied simultaneously to achieve various targets of ignition timing, combustion phasing, overall burn duration, emissions, fuel consumption, peak cylinder pressure and maximum pressure rise rate. The baseline case was a three-dimensional closed-cycle computational fluid dynamics (CFD) simulation with a sector mesh at medium load conditions. Eleven design parameters were considered and ranges of variation were prescribed to each of these. These input variables were perturbed in their respective ranges using the Monte Carlo (MC) method to generate a set of 256 CFD simulations and the targets were calculated from the simulation results. GSA was then applied as a screening tool to identify the input parameters having the most

2-Methylfuran: A bio-derived octane booster for spark-ignition engines

KAUST Repository

Sarathy, Mani

2018-04-02

The efficiency of spark-ignition engines is limited by the phenomenon of knock, which is caused by auto-ignition of the fuel-air mixture ahead of the spark-initiated flame front. The resistance of a fuel to knock is quantified by its octane index; therefore, increasing the octane index of a spark-ignition engine fuel increases the efficiency of the respective engine. However, raising the octane index of gasoline increases the refining costs, as well as the energy consumption during production. The use of alternative fuels with synergistic blending effects presents an attractive option for improving octane index. In this work, the octane enhancing potential of 2-methylfuran (2-MF), a next-generation biofuel, has been examined and compared to other high-octane components (i.e., ethanol and toluene). A primary reference fuel with an octane index of 60 (PRF60) was chosen as the base fuel since it closely represents refinery naphtha streams, which are used as gasoline blend stocks. Initial screening of the fuels was done in an ignition quality tester (IQT). The PRF60/2-MF (80/20 v/v%) blend exhibited longer ignition delay times compared to PRF60/ethanol (80/20 v/v%) blend and PRF60/toluene (80/20 v/v%) blend, even though pure 2-MF is more reactive than both ethanol and toluene. The mixtures were also tested in a cooperative fuels research (CFR) engine under research octane number and motor octane number like conditions. The PRF60/2-MF blend again possesses a higher octane index than other blending components. A detailed chemical kinetic analysis was performed to understand the synergetic blending effect of 2-MF, using a well-validated PRF/2-MF kinetic model. Kinetic analysis revealed superior suppression of low-temperature chemistry with the addition of 2-MF. The results from simulations were further confirmed by homogeneous charge compression ignition engine experiments, which established its superior low-temperature heat release (LTHR) suppression compared to ethanol

Effects of time delay on stochastic resonance of the stock prices in financial system

Energy Technology Data Exchange (ETDEWEB)

Li, Jiang-Cheng [Department of Physics, Yunnan University, Kunming, 650091 (China); Li, Chun [Department of Computer Science, Puer Teachers' College, Puer 665000 (China); Mei, Dong-Cheng, E-mail: meidch@ynu.edu.cn [Department of Physics, Yunnan University, Kunming, 650091 (China)

2014-06-13

The effect of time delay on stochastic resonance of the stock prices in finance system was investigated. The time delay is introduced into the Heston model driven by the extrinsic and intrinsic periodic information for stock price. The signal power amplification (SPA) was calculated by numerical simulation. The results indicate that an optimal critical value of delay time maximally enhances the reverse-resonance in the behaviors of SPA as a function of long-run variance of volatility or cross correlation coefficient between noises for both cases of intrinsic and extrinsic periodic information. Moreover, in both cases, being a critical value in the delay time, when the delay time takes value below the critical value, reverse-resonance increases with the delay time increasing, however, when the delay time takes value above the critical value, the reverse-resonance decrease with the delay time increasing. - Highlights: • The effects of delay time on stochastic resonance of the stock prices was investigated. • There is an optimal critical value of delay time maximally enhances the reverse-resonance • The reverse-resonance increases with the delay time increasing as the delay time takes value below the critical value • The reverse-resonance decrease with the delay time increasing as the delay time takes value above the critical value.

Effects of time delay on stochastic resonance of the stock prices in financial system

International Nuclear Information System (INIS)

Li, Jiang-Cheng; Li, Chun; Mei, Dong-Cheng

2014-01-01

The effect of time delay on stochastic resonance of the stock prices in finance system was investigated. The time delay is introduced into the Heston model driven by the extrinsic and intrinsic periodic information for stock price. The signal power amplification (SPA) was calculated by numerical simulation. The results indicate that an optimal critical value of delay time maximally enhances the reverse-resonance in the behaviors of SPA as a function of long-run variance of volatility or cross correlation coefficient between noises for both cases of intrinsic and extrinsic periodic information. Moreover, in both cases, being a critical value in the delay time, when the delay time takes value below the critical value, reverse-resonance increases with the delay time increasing, however, when the delay time takes value above the critical value, the reverse-resonance decrease with the delay time increasing. - Highlights: • The effects of delay time on stochastic resonance of the stock prices was investigated. • There is an optimal critical value of delay time maximally enhances the reverse-resonance • The reverse-resonance increases with the delay time increasing as the delay time takes value below the critical value • The reverse-resonance decrease with the delay time increasing as the delay time takes value above the critical value

Gain curves and hydrodynamic modeling for shock ignition

International Nuclear Information System (INIS)

Lafon, M.; Ribeyre, X.; Schurtz, G.

2010-01-01

Ignition of a precompressed thermonuclear fuel by means of a converging shock is now considered as a credible scheme to obtain high gains for inertial fusion energy. This work aims at modeling the successive stages of the fuel time history, from compression to final thermonuclear combustion, in order to provide the gain curves of shock ignition (SI). The leading physical mechanism at work in SI is pressure amplification, at first by spherical convergence, and by collision with the shock reflected at center during the stagnation process. These two effects are analyzed, and ignition conditions are provided as functions of the shock pressure and implosion velocity. Ignition conditions are obtained from a non-isobaric fuel assembly, for which we present a gain model. The corresponding gain curves exhibit a significantly lower ignition threshold and higher target gains than conventional central ignition.

Review of the National Ignition Campaign 2009-2012

International Nuclear Information System (INIS)

Lindl, John; Landen, Otto; Edwards, John; Moses, Ed

2014-01-01

The National Ignition Campaign (NIC) was a multi-institution effort established under the National Nuclear Security Administration of DOE in 2005, prior to the completion of the National Ignition Facility (NIF) in 2009. The scope of the NIC was the planning and preparation for and the execution of the first 3 yr of ignition experiments (through the end of September 2012) as well as the development, fielding, qualification, and integration of the wide range of capabilities required for ignition. Besides the operation and optimization of the use of NIF, these capabilities included over 50 optical, x-ray, and nuclear diagnostic systems, target fabrication facilities, experimental platforms, and a wide range of NIF facility infrastructure. The goal of ignition experiments on the NIF is to achieve, for the first time, ignition and thermonuclear burn in the laboratory via inertial confinement fusion and to develop a platform for ignition and high energy density applications on the NIF. The goal of the NIC was to develop and integrate all of the capabilities required for a precision ignition campaign and, if possible, to demonstrate ignition and gain by the end of FY12. The goal of achieving ignition can be divided into three main challenges. The first challenge is defining specifications for the target, laser, and diagnostics with the understanding that not all ignition physics is fully understood and not all material properties are known. The second challenge is designing experiments to systematically remove these uncertainties. The third challenge is translating these experimental results into metrics designed to determine how well the experimental implosions have performed relative to expectations and requirements and to advance those metrics toward the conditions required for ignition. This paper summarizes the approach taken to address these challenges, along with the progress achieved to date and the challenges that remain. At project completion in 2009, NIF lacked

STUDY OF CHIP IGNITION AND CHIP MORPHOLOGY AFTER MILLING OF MAGNESIUM ALLOYS

Directory of Open Access Journals (Sweden)

Ireneusz Zagórski

2016-12-01

Full Text Available The paper analyses the impact of specified technological parameters of milling (vc, fz, ap on time to ignition. Stages leading to chip ignition were analysed. Metallographic images of magnesium chip were presented. No significant difference was observed in time to ignition in different chip fractions. Moreover, the surface of chips was free of products of ignition and signs of strong oxidation.

Low-complexity controllers for time-delay systems

CERN Document Server

Özbay, Hitay; Bonnet, Catherine; Mounier, Hugues

2014-01-01

This volume in the newly established series Advances in Delays and Dynamics (ADD@S) provides a collection of recent results on the design and analysis of Low Complexity Controllers for Time Delay Systems. A widely used indirect method to obtain low order controllers for time delay systems is to design a controller for the reduced order model of the plant. In the dual indirect approach, an infinite dimensional controller is designed first for the original plant model; then, the controller is approximated by keeping track of the degradation in performance and stability robustness measures. The present volume includes new techniques used at different stages of the indirect approach. It also includes new direct design methods for fixed structure and low order controllers. On the other hand, what is meant by low complexity controller is not necessarily low order controller. For example, Smith predictor or similar type of controllers include a copy of the plant internally in the controller, so they are technically ...

Determination of Uncalibrated Phase Delays for Real-Time PPP

Science.gov (United States)

Hinterberger, Fabian; Weber, Robert; Huber, Katrin; Lesjak, Roman

2014-05-01

Today PPP is a well-known technique of GNSS based positioning used for a wide range of post-processing applications. Using observations of a single GNSS receiver and applying precise orbit and clock information derived from global GNSS networks highly precise positions can be obtained. The atmospheric delays are usually mitigated by linear combination (ionosphere) and parameter estimation (troposphere). Within the last years also the demand for real-time PPP increased. In 2012, the IGS real-time working group started a pilot project to broadcast real-time precise orbits and clock correction streams. Nevertheless, real-time PPP is in its starting phase and currently only few applications make use of the technique although SSR-Messages are already implemented in RTCM3.1. The problems of still limited accuracy compared to Network-RTK as well as long convergence times might be solved by almost instantaneous integer ambiguity resolution at zero-difference level which is a major topic of current scientific investigations. Therefore a national consortium has carried out over the past 2 years the research project PPP-Serve (funded by the Austrian Research Promotion Agency - FFG), which aimed at the development of appropriate algorithms for real-time PPP with special emphasis on the ambiguity resolution of zero-difference observations. We have established a module which calculates based on GPS-reference station data-streams of a dense network (obtained from IGS via BKG) so-called wide-lane and narrow-lane satellite specific calibration phase delays. While the wide-lane phase delays are almost stable over longer periods, the estimation of narrow-lane phase delays has to be re-established every 24 hours. These phase-delays are submitted via a real-time module to the rover where they are used for point positioning via a PPP-model. This presentation deals with the process and obstacles of calculating the wide-lane and narrow-lane phase-delays (based on SD -observations between

Lesions Responsible for Delayed Oral Transit Time in Post-stroke Dysphagia.

Science.gov (United States)

Moon, Hyun Im; Yoon, Seo Yeon; Yi, Tae Im; Jeong, Yoon Jeong; Cho, Tae Hwan

2017-10-11

Some stroke patients show oral phase dysphagia, characterized by a markedly prolonged oral transit time that hinders oral feeding. The aim of this study was to clarify the clinical characteristics and lesions responsible for delayed swallowing. We reviewed 90 patients with stroke. The oral processing time plus the postfaucial aggregation time required to swallow semisolid food was assessed. The patients were divided into two groups according to oral transit time, and we analyzed the differences in characteristics such as demographic factors, lesion factors, and cognitive function. Logistic regression analyses were performed to examine the predictors of delayed oral transit time. Lesion location and volume were measured on brain magnetic resonance images. We generated statistic maps of lesions related to delayed oral phase in swallowing using voxel-based lesion symptom mapping (VLSM). The group of patients who showed delayed oral transit time had significantly low cognitive function. Also, in a regression model, delayed oral phase was predicted with low K-MMSE (Korean version of the Mini Mental Status Exam). Using VLSM, we found the lesion location to be associated with delayed oral phase after adjusting for K-MMSE score. Although these results did not reach statistical significance, they showed the lesion pattern with predominant distribution in the left frontal lobe. Delayed oral phase in post-stroke patients was not negligible clinically. Patients' cognitive impairments affect the oral transit time. When adjusting it, we found a trend that the lesion responsible for delayed oral phase was located in the left frontal lobe, though the association did not reach significance. The delay might be related to praxis function.

Micromachined silicon parallel acoustic delay lines as time-delayed ultrasound detector array for real-time photoacoustic tomography

Science.gov (United States)

Cho, Y.; Chang, C.-C.; Wang, L. V.; Zou, J.

2016-02-01

This paper reports the development of a new 16-channel parallel acoustic delay line (PADL) array for real-time photoacoustic tomography (PAT). The PADLs were directly fabricated from single-crystalline silicon substrates using deep reactive ion etching. Compared with other acoustic delay lines (e.g., optical fibers), the micromachined silicon PADLs offer higher acoustic transmission efficiency, smaller form factor, easier assembly, and mass production capability. To demonstrate its real-time photoacoustic imaging capability, the silicon PADL array was interfaced with one single-element ultrasonic transducer followed by one channel of data acquisition electronics to receive 16 channels of photoacoustic signals simultaneously. A PAT image of an optically-absorbing target embedded in an optically-scattering phantom was reconstructed, which matched well with the actual size of the imaged target. Because the silicon PADL array allows a signal-to-channel reduction ratio of 16:1, it could significantly simplify the design and construction of ultrasonic receivers for real-time PAT.

Micromachined silicon parallel acoustic delay lines as time-delayed ultrasound detector array for real-time photoacoustic tomography

International Nuclear Information System (INIS)

Cho, Y; Chang, C-C; Zou, J; Wang, L V

2016-01-01

This paper reports the development of a new 16-channel parallel acoustic delay line (PADL) array for real-time photoacoustic tomography (PAT). The PADLs were directly fabricated from single-crystalline silicon substrates using deep reactive ion etching. Compared with other acoustic delay lines (e.g., optical fibers), the micromachined silicon PADLs offer higher acoustic transmission efficiency, smaller form factor, easier assembly, and mass production capability. To demonstrate its real-time photoacoustic imaging capability, the silicon PADL array was interfaced with one single-element ultrasonic transducer followed by one channel of data acquisition electronics to receive 16 channels of photoacoustic signals simultaneously. A PAT image of an optically-absorbing target embedded in an optically-scattering phantom was reconstructed, which matched well with the actual size of the imaged target. Because the silicon PADL array allows a signal-to-channel reduction ratio of 16:1, it could significantly simplify the design and construction of ultrasonic receivers for real-time PAT. (paper)

Investigating antennas as ignition aid for automotive HID lamps

International Nuclear Information System (INIS)

Bergner, A; Engelhardt, M; Bienholz, S; Ruhrmann, C; Hoebing, T; Groeger, S; Mentel, J; Awakowicz, P

2015-01-01

This paper considers the ignition of mercury-free high-intensity discharge (HID) lamps for car headlights. Due to safety reasons, these lamps need to have a fast run-up phase which is ensured, amongst other things, by a high Xe pressure of roughly 15 bar (cold) in the discharge vessel. The high Xe pressure causes an increased ignition voltage compared with former mercury-containing automotive HID lamps or low-pressure lamps used for general-lighting applications. The increase in ignition voltage can be limited if the electric field in front of the electrodes is raised by an uplifting of the electrical conductivity along the outer wall of the inner bulb either by a conductive layer on its surface or by a dielectric barrier discharge (DBD) within the outer bulb. This paper considers on the one hand conventional antennas deposited by physical vapour deposition (PVD) and on the other hand a combination of these antennas with a DBD within the outer-bulb operated in 100 mbar Ar as ignition aids. In both cases the antenna potential and antenna width are varied. Additionally, the effects of antenna thickness and antenna material are investigated. The ignition voltage, ignition current and light emission during ignition are measured on a nanosecond timescale. Furthermore, for the very first time, the ignition process is recorded in four consecutive intensified charge-coupled device images using a high-speed camera system with a time resolution in the range of nanoseconds. It was found that antennas strongly reduce the ignition voltage of automotive HID lamps. Active antennas reduce the ignition voltage significantly more than passive antennas, proportional to the conductance of the antenna. Combining conventional antennas with an outer-bulb discharge reduces the ignition voltage from 19 kV without any ignition aid to the intrinsic ignition voltage of the lamp below 10 kV, in the best case. (paper)

Time delay for resonant vibrational excitation in electron--molecule collisions

International Nuclear Information System (INIS)

Gauyacq, J.P.

1990-01-01

An analysis of the time delay associated with vibrational excitation in electron--molecule collision is presented. It consists of a direct study of the time dependence of the process for three model systems. An electron wave packet, that is narrow in time, is sent on the target and the amplitudes in the different inelastic channels are studied as functions of time. The time delay is found to correspond to very different time effects: broadenings, shifts in time of the wave packet, but also complex distortions that cannot be represented by a time delay. The direct analysis of the scattered wave also provides new insights into the vibrational excitation process. It should be a useful tool to analyze complex collision processes

Losing track of time through delayed body representations.

Science.gov (United States)

Fritz, Thomas H; Steixner, Agnes; Boettger, Joachim; Villringer, Arno

2015-01-01

The ability to keep track of time is perceived as crucial in most human societies. However, to lose track of time may also serve an important social role, associated with recreational purpose. To this end a number of social technologies are employed, some of which may relate to a manipulation of time perception through a modulation of body representation. Here, we investigated an influence of real-time or delayed videos of own-body representations on time perception in an experimental setup with virtual mirrors. Seventy participants were asked to either stay in the installation until they thought that a defined time (90 s) had passed, or they were encouraged to stay in the installation as long as they wanted and after exiting were asked to estimate the duration of their stay. Results show that a modulation of body representation by time-delayed representations of the mirror-video displays influenced time perception. Furthermore, these time-delayed conditions were associated with a greater sense of arousal and intoxication. We suggest that feeding in references to the immediate past into working memory could be the underlying mental mechanism mediating the observed modulation of time perception. We argue that such an influence on time perception would probably not only be achieved visually, but might also work with acoustic references to the immediate past (e.g., with music).

Losing track of time through delayed body representations

Directory of Open Access Journals (Sweden)

Thomas Hans Fritz

2015-04-01

Full Text Available The ability to keep track of time is perceived as crucial in most human societies. However, to lose track of time may also serve an important social role, associated with recreational purpose. To this end a number of social technologies are employed, some of which may relate to a manipulation of time perception through a modulation of body representation. Here we investigated an influence of real-time or delayed videos of own-body representations on time perception in an experimental setup with virtual mirrors. Seventy participants were asked to either stay in the installation until they thought that a defined time (90 s had passed, or they were encouraged to stay in the installation as long as they wanted and after exiting were asked to estimate the duration of their stay. Results show that a modulation of body representation by time-delayed representations of the mirror-video displays influenced time perception. Furthermore, these time-delayed conditions were associated with a greater sense of arousal and intoxication. We suggest that feeding in references to the immediate past into working memory could be the underlying mental mechanism mediating the observed modulation of time perception. We argue that such an influence on time perception would probably not only be achieved visually, but might also work with acoustic references to the immediate past (e.g., with music.

Stochastic nonlinear time series forecasting using time-delay reservoir computers: performance and universality.

Science.gov (United States)

Grigoryeva, Lyudmila; Henriques, Julie; Larger, Laurent; Ortega, Juan-Pablo

2014-07-01

Reservoir computing is a recently introduced machine learning paradigm that has already shown excellent performances in the processing of empirical data. We study a particular kind of reservoir computers called time-delay reservoirs that are constructed out of the sampling of the solution of a time-delay differential equation and show their good performance in the forecasting of the conditional covariances associated to multivariate discrete-time nonlinear stochastic processes of VEC-GARCH type as well as in the prediction of factual daily market realized volatilities computed with intraday quotes, using as training input daily log-return series of moderate size. We tackle some problems associated to the lack of task-universality for individually operating reservoirs and propose a solution based on the use of parallel arrays of time-delay reservoirs. Copyright © 2014 Elsevier Ltd. All rights reserved.

New delay-dependent absolute stability criteria for Lur'e systems with time-varying delay

Science.gov (United States)

Chen, Yonggang; Bi, Weiping; Li, Wenlin

2011-07-01

In this article, the absolute stability problem is investigated for Lur'e systems with time-varying delay and sector-bounded nonlinearity. By employing the delay fractioning idea, the new augmented Lyapunov functional is first constructed. Then, by introducing some slack matrices and by reserving the useful term when estimating the upper bound of the derivative of Lyapunov functional, the new delay-dependent absolute stability criteria are derived in terms of linear matrix inequalities. Several numerical examples are presented to show the effectiveness and the less conservativeness of the proposed method.

Low power arcjet thruster pulse ignition

Science.gov (United States)

Sarmiento, Charles J.; Gruber, Robert P.

1987-01-01

An investigation of the pulse ignition characteristics of a 1 kW class arcjet using an inductive energy storage pulse generator with a pulse width modulated power converter identified several thruster and pulse generator parameters that influence breakdown voltage including pulse generator rate of voltage rise. This work was conducted with an arcjet tested on hydrogen-nitrogen gas mixtures to simulate fully decomposed hydrazine. Over all ranges of thruster and pulser parameters investigated, the mean breakdown voltages varied from 1.4 to 2.7 kV. Ignition tests at elevated thruster temperatures under certain conditions revealed occasional breakdowns to thruster voltages higher than the power converter output voltage. These post breakdown discharges sometimes failed to transition to the lower voltage arc discharge mode and the thruster would not ignite. Under the same conditions, a transition to the arc mode would occur for a subsequent pulse and the thruster would ignite. An automated 11 600 cycle starting and transition to steady state test demonstrated ignition on the first pulse and required application of a second pulse only two times to initiate breakdown.

Contactless Electric Igniter for Vehicle to Lower Exhaust Emission and Fuel Consumption

Directory of Open Access Journals (Sweden)

Chih-Lung Shen

2014-01-01

Full Text Available An electric igniter for engine/hybrid vehicles is presented. The igniter comprises a flyback converter, a voltage-stacked capacitor, a PIC-based controller, a differential voltage detector, and an ignition coil, of which structure is non-contact type. Since the electric igniter adopts a capacitor to accumulate energy for engine ignition instead of traditional contacttype approach, it enhances the igniting performance of a spark plug effectively. As a result, combustion efficiency is promoted, fuel consumption is saved, and exhaust emission is reduced. The igniter not only is good for fuel efficiency but also can reduce HC and CO emission significantly, which therefore is an environmentally friendly product. The control core of the igniter is implemented on a single chip, which lowers discrete component count, reduces system volume, and increases reliability. In addition, the ignition timing can be programmed so that a timing regulator can be removed from the proposed system, simplifying its structure. To verify the feasibility and functionality of the igniter, key waveforms are measured and real-car experiments are performed as well.

Managing contamination delay to improve Timing Speculation architectures

Directory of Open Access Journals (Sweden)

Naga Durga Prasad Avirneni

2016-08-01

Full Text Available Timing Speculation (TS is a widely known method for realizing better-than-worst-case systems. Aggressive clocking, realizable by TS, enable systems to operate beyond specified safe frequency limits to effectively exploit the data dependent circuit delay. However, the range of aggressive clocking for performance enhancement under TS is restricted by short paths. In this paper, we show that increasing the lengths of short paths of the circuit increases the effectiveness of TS, leading to performance improvement. Also, we propose an algorithm to efficiently add delay buffers to selected short paths while keeping down the area penalty. We present our algorithm results for ISCAS-85 suite and show that it is possible to increase the circuit contamination delay by up to 30% without affecting the propagation delay. We also explore the possibility of increasing short path delays further by relaxing the constraint on propagation delay and analyze the performance impact.

New Approach to Study the Ignition Processes of Organic Coal-Water Fuels in an Oxidizer Flow

Directory of Open Access Journals (Sweden)

Valiullin T.R.

2016-01-01

Full Text Available To converge the conditions of organic water-coal fuel composition combustion in the typical power equipment we developed a new approach and installed an experimental setup, eliminating the traditional fixing the fuel droplets on the thermocouples or rods. Specialized cone-shaped chamber was used to implement the process of lingering of organic water-coal fuel droplets. Necessary and sufficient conditions for the lingering of organic water-coal fuel droplets were established. We determined the parameters of the system (droplet size of 0.4-0.6 mm, temperatures 823-903 K and the velocity of the oxidizer flow 1.5-6 m/s at which the droplets were consistently ignited in the process of lingering. Minimum temperatures and ignition delay times of organic water-coal fuel droplets based on brown coal, used motor, turbine, transformer oils, kerosene, gasoline and water were defined.

A delay-dependent LMI approach to dynamics analysis of discrete-time recurrent neural networks with time-varying delays

International Nuclear Information System (INIS)

Song, Qiankun; Wang, Zidong

2007-01-01

In this Letter, the analysis problem for the existence and stability of periodic solutions is investigated for a class of general discrete-time recurrent neural networks with time-varying delays. For the neural networks under study, a generalized activation function is considered, and the traditional assumptions on the boundedness, monotony and differentiability of the activation functions are removed. By employing the latest free-weighting matrix method, an appropriate Lyapunov-Krasovskii functional is constructed and several sufficient conditions are established to ensure the existence, uniqueness, and globally exponential stability of the periodic solution for the addressed neural network. The conditions are dependent on both the lower bound and upper bound of the time-varying time delays. Furthermore, the conditions are expressed in terms of the linear matrix inequalities (LMIs), which can be checked numerically using the effective LMI toolbox in MATLAB. Two simulation examples are given to show the effectiveness and less conservatism of the proposed criteria

Delay-Dependent Asymptotic Stability of Cohen-Grossberg Models with Multiple Time-Varying Delays

Directory of Open Access Journals (Sweden)

Xiaofeng Liao

2007-01-01

Full Text Available Dynamical behavior of a class of Cohen-Grossberg models with multiple time-varying delays is studied in detail. Sufficient delay-dependent criteria to ensure local and global asymptotic stabilities of the equilibrium of this network are derived by constructing suitable Lyapunov functionals. The obtained conditions are shown to be less conservative and restrictive than those reported in the known literature. Some numerical examples are included to demonstrate our results.

Delay-Dependent Stability Criteria of Uncertain Periodic Switched Recurrent Neural Networks with Time-Varying Delays

Directory of Open Access Journals (Sweden)

Xing Yin

2011-01-01

uncertain periodic switched recurrent neural networks with time-varying delays. When uncertain discrete-time recurrent neural network is a periodic system, it is expressed as switched neural network for the finite switching state. Based on the switched quadratic Lyapunov functional approach (SQLF and free-weighting matrix approach (FWM, some linear matrix inequality criteria are found to guarantee the delay-dependent asymptotical stability of these systems. Two examples illustrate the exactness of the proposed criteria.

Spatial determination of magnetic avalanche ignition points

International Nuclear Information System (INIS)

Jaafar, Reem; McHugh, S.; Suzuki, Yoko; Sarachik, M.P.; Myasoedov, Y.; Zeldov, E.; Shtrikman, H.; Bagai, R.; Christou, G.

2008-01-01

Using time-resolved measurements of local magnetization in the molecular magnet Mn 12 -ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends

Spatial determination of magnetic avalanche ignition points

Energy Technology Data Exchange (ETDEWEB)

Jaafar, Reem; McHugh, S.; Suzuki, Yoko [Physics Department, City College of the City University of New York, New York, NY 10031 (United States); Sarachik, M.P. [Physics Department, City College of the City University of New York, New York, NY 10031 (United States)], E-mail: sarachik@sci.ccny.cuny.edu; Myasoedov, Y.; Zeldov, E.; Shtrikman, H. [Department Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Bagai, R.; Christou, G. [Department of Chemistry, University of Florida, Gainesville, FL 32611 (United States)

2008-03-15

Using time-resolved measurements of local magnetization in the molecular magnet Mn{sub 12}-ac, we report studies of magnetic avalanches (fast magnetization reversals) with non-planar propagating fronts, where the curved nature of the magnetic fronts is reflected in the time-of-arrival at micro-Hall sensors placed at the surface of the sample. Assuming that the avalanche interface is a spherical bubble that grows with a radius proportional to time, we are able to locate the approximate ignition point of each avalanche in a two-dimensional cross-section of the crystal. We find that although in most samples the avalanches ignite at the long ends, as found in earlier studies, there are crystals in which ignition points are distributed throughout an entire weak region near the center, with a few avalanches still originating at the ends.

Stability analysis of fractional-order Hopfield neural networks with time delays.

Science.gov (United States)

Wang, Hu; Yu, Yongguang; Wen, Guoguang

2014-07-01

This paper investigates the stability for fractional-order Hopfield neural networks with time delays. Firstly, the fractional-order Hopfield neural networks with hub structure and time delays are studied. Some sufficient conditions for stability of the systems are obtained. Next, two fractional-order Hopfield neural networks with different ring structures and time delays are developed. By studying the developed neural networks, the corresponding sufficient conditions for stability of the systems are also derived. It is shown that the stability conditions are independent of time delays. Finally, numerical simulations are given to illustrate the effectiveness of the theoretical results obtained in this paper. Copyright © 2014 Elsevier Ltd. All rights reserved.

Modelling piloted ignition of wood and plastics

NARCIS (Netherlands)

Blijderveen, M.; Bramer, Eduard A.; Brem, Gerrit

2012-01-01

To gain insight in the startup of an incinerator, this article deals with piloted ignition. A newly developed model is described to predict the piloted ignition times of wood, PMMA and PVC. The model is based on the lower flammability limit and the adiabatic flame temperature at this limit. The

Discrete-time recurrent neural networks with time-varying delays: Exponential stability analysis

International Nuclear Information System (INIS)

Liu, Yurong; Wang, Zidong; Serrano, Alan; Liu, Xiaohui

2007-01-01

This Letter is concerned with the analysis problem of exponential stability for a class of discrete-time recurrent neural networks (DRNNs) with time delays. The delay is of the time-varying nature, and the activation functions are assumed to be neither differentiable nor strict monotonic. Furthermore, the description of the activation functions is more general than the recently commonly used Lipschitz conditions. Under such mild conditions, we first prove the existence of the equilibrium point. Then, by employing a Lyapunov-Krasovskii functional, a unified linear matrix inequality (LMI) approach is developed to establish sufficient conditions for the DRNNs to be globally exponentially stable. It is shown that the delayed DRNNs are globally exponentially stable if a certain LMI is solvable, where the feasibility of such an LMI can be easily checked by using the numerically efficient Matlab LMI Toolbox. A simulation example is presented to show the usefulness of the derived LMI-based stability condition

Incorporation of Time Delayed Measurements in a Discrete-time Kalman Filter

DEFF Research Database (Denmark)

Larsen, Thomas Dall; Andersen, Nils Axel; Ravn, Ole

1998-01-01

In many practical systems there is a delay in some of the sensor devices, for instance vision measurements that may have a long processing time. How to fuse these measurements in a Kalman filter is not a trivial problem if the computational delay is critical. Depending on how much time...... using past and present estimates of the Kalman filter and calculating an optimal gain for this extrapolated measurement...... there is at hand, the designer has to make trade offs between optimality and computational burden of the filter. In this paper various methods in the literature along with a new method proposed by the authors will be presented and compared. The new method is based on “extrapolating” the measurement to present time...

Computational Fluid Dynamics Study on the Effects of RATO Timing on the Scale Model Acoustic Test

Science.gov (United States)

Nielsen, Tanner; Williams, B.; West, Jeff

2015-01-01

The Scale Model Acoustic Test (SMAT) is a 5% scale test of the Space Launch System (SLS), which is currently being designed at Marshall Space Flight Center (MSFC). The purpose of this test is to characterize and understand a variety of acoustic phenomena that occur during the early portions of lift off, one being the overpressure environment that develops shortly after booster ignition. The SLS lift off configuration consists of four RS-25 liquid thrusters on the core stage, with two solid boosters connected to each side. Past experience with scale model testing at MSFC (in ER42), has shown that there is a delay in the ignition of the Rocket Assisted Take Off (RATO) motor, which is used as the 5% scale analog of the solid boosters, after the signal to ignite is given. This delay can range from 0 to 16.5ms. While this small of a delay maybe insignificant in the case of the full scale SLS, it can significantly alter the data obtained during the SMAT due to the much smaller geometry. The speed of sound of the air and combustion gas constituents is not scaled, and therefore the SMAT pressure waves propagate at approximately the same speed as occurs during full scale. However, the SMAT geometry is much smaller allowing the pressure waves to move down the exhaust duct, through the trench, and impact the vehicle model much faster than occurs at full scale. To better understand the effect of the RATO timing simultaneity on the SMAT IOP test data, a computational fluid dynamics (CFD) analysis was performed using the Loci/CHEM CFD software program. Five different timing offsets, based on RATO ignition delay statistics, were simulated. A variety of results and comparisons will be given, assessing the overall effect of RATO timing simultaneity on the SMAT overpressure environment.

Fundamental and Subharmonic Resonances of Harmonically Oscillation with Time Delay State Feedback

Directory of Open Access Journals (Sweden)

A.F. EL-Bassiouny

2006-01-01

Full Text Available Time delays occur in many physical systems. In particular, when automatic control is used with structural or mechanical systems, there exists a delay between measurement of the system state and corrective action. The concept of an equivalent damping related to the delay feedback is proposed and the appropriate choice of the feedback gains and the time delay is discussed from the viewpoint of vibration control. We investigate the fundamental resonance and subharmonic resonance of order one-half of a harmonically oscillation under state feedback control with a time delay. By using the multiple scale perturbation technique, the first order approximation of the resonances are derived and the effect of time delay on the resonances is investigated. The fixed points correspond to a periodic motion for the starting system and we show the external excitation-response and frequency-response curves. We analyze the effect of time delay and the other different parameters on these oscillations.

1D radiation analysis for the fusion ignition experiment ZEPHYR

International Nuclear Information System (INIS)

Brockmann, H.; Ohlig, U.; Krause, H.

1979-11-01

For the proposed tokamak ignition experiment ZEPHYR a nuclear radiation analysis is performed for both the prompt radiation during a discharge and the delayed radiation after discharges. This analysis is restricted to a one-dimensional geometrical approximation of the apparatus. Nuclear heating data are derived for the prompt radiation and the shielding concept is investigated. Results for the delayed radiation are given for three activation scenarios, that are anticipated for machine operation. The cooling phase after one of these scenarios is investigated in some detail in order to trace the dominant contributions to biological dose rates back to machine components and to specific activation reactions. (orig.)

Asymptotic stability of discrete-time systems with time-varying delay subject to saturation nonlinearities

International Nuclear Information System (INIS)

Chen, S.-F.

2009-01-01

The asymptotic stability problem for discrete-time systems with time-varying delay subject to saturation nonlinearities is addressed in this paper. In terms of linear matrix inequalities (LMIs), a delay-dependent sufficient condition is derived to ensure the asymptotic stability. A numerical example is given to demonstrate the theoretical results.

Laser Ignition Technology for Bi-Propellant Rocket Engine Applications

Science.gov (United States)

Thomas, Matthew E.; Bossard, John A.; Early, Jim; Trinh, Huu; Dennis, Jay; Turner, James (Technical Monitor)

2001-01-01

The fiber optically coupled laser ignition approach summarized is under consideration for use in igniting bi-propellant rocket thrust chambers. This laser ignition approach is based on a novel dual pulse format capable of effectively increasing laser generated plasma life times up to 1000 % over conventional laser ignition methods. In the dual-pulse format tinder consideration here an initial laser pulse is used to generate a small plasma kernel. A second laser pulse that effectively irradiates the plasma kernel follows this pulse. Energy transfer into the kernel is much more efficient because of its absorption characteristics thereby allowing the kernel to develop into a much more effective ignition source for subsequent combustion processes. In this research effort both single and dual-pulse formats were evaluated in a small testbed rocket thrust chamber. The rocket chamber was designed to evaluate several bipropellant combinations. Optical access to the chamber was provided through small sapphire windows. Test results from gaseous oxygen (GOx) and RP-1 propellants are presented here. Several variables were evaluated during the test program, including spark location, pulse timing, and relative pulse energy. These variables were evaluated in an effort to identify the conditions in which laser ignition of bi-propellants is feasible. Preliminary results and analysis indicate that this laser ignition approach may provide superior ignition performance relative to squib and torch igniters, while simultaneously eliminating some of the logistical issues associated with these systems. Further research focused on enhancing the system robustness, multiplexing, and window durability/cleaning and fiber optic enhancements is in progress.

Chemical Kinetics of Hydrocarbon Ignition in Practical Combustion Systems

International Nuclear Information System (INIS)

Westbrook, C.K.

2000-01-01

Chemical kinetic factors of hydrocarbon oxidation are examined in a variety of ignition problems. Ignition is related to the presence of a dominant chain branching reaction mechanism that can drive a chemical system to completion in a very short period of time. Ignition in laboratory environments is studied for problems including shock tubes and rapid compression machines. Modeling of the laboratory systems are used to develop kinetic models that can be used to analyze ignition in practical systems. Two major chain branching regimes are identified, one consisting of high temperature ignition with a chain branching reaction mechanism based on the reaction between atomic hydrogen with molecular oxygen, and the second based on an intermediate temperature thermal decomposition of hydrogen peroxide. Kinetic models are then used to describe ignition in practical combustion environments, including detonations and pulse combustors for high temperature ignition, and engine knock and diesel ignition for intermediate temperature ignition. The final example of ignition in a practical environment is homogeneous charge, compression ignition (HCCI) which is shown to be a problem dominated by the kinetics intermediate temperature hydrocarbon ignition. Model results show why high hydrocarbon and CO emissions are inevitable in HCCI combustion. The conclusion of this study is that the kinetics of hydrocarbon ignition are actually quite simple, since only one or two elementary reactions are dominant. However, there are many combustion factors that can influence these two major reactions, and these are the features that vary from one practical system to another

Confinement scaling and ignition in tokamaks

International Nuclear Information System (INIS)

Perkins, F.W.; Sun, Y.C.

1985-10-01

A drift wave turbulence model is used to compute the scaling and magnitude of central electron temperature and confinement time of tokamak plasmas. The results are in accord with experiment. Application to ignition experiments shows that high density (1 to 2) . 10 15 cm -3 , high field, B/sub T/ > 10 T, but low temperature T approx. 6 keV constitute the optimum path to ignition

Local Stability of AIDS Epidemic Model Through Treatment and Vertical Transmission with Time Delay

Science.gov (United States)

Novi W, Cascarilla; Lestari, Dwi

2016-02-01

This study aims to explain stability of the spread of AIDS through treatment and vertical transmission model. Human with HIV need a time to positively suffer AIDS. The existence of a time, human with HIV until positively suffer AIDS can be delayed for a time so that the model acquired is the model with time delay. The model form is a nonlinear differential equation with time delay, SIPTA (susceptible-infected-pre AIDS-treatment-AIDS). Based on SIPTA model analysis results the disease free equilibrium point and the endemic equilibrium point. The disease free equilibrium point with and without time delay are local asymptotically stable if the basic reproduction number is less than one. The endemic equilibrium point will be local asymptotically stable if the time delay is less than the critical value of delay, unstable if the time delay is more than the critical value of delay, and bifurcation occurs if the time delay is equal to the critical value of delay.

Characteristics of Syngas Auto-ignition at High Pressure and Low Temperature Conditions with Thermal Inhomogeneities

KAUST Repository

Pal, Pinaki; Mansfield, Andrew B.; Wooldridge, Margaret S.; Im, Hong G.

2015-01-01

Effects of thermal inhomogeneities on syngas auto-ignition at high-pressure low-temperature conditions, relevant to gas turbine operation, are investigated using detailed one-dimensional numerical simulations. Parametric tests are carried out for a range of thermodynamic conditions (T = 890-1100 K, P = 3-20 atm) and composition (Ф = 0.1, 0.5). Effects of global thermal gradients and localized thermal hot spots are studied. In the presence of a thermal gradient, the propagating reaction front transitions from spontaneous ignition to deflagration mode as the initial mean temperature decreases. The critical mean temperature separating the two distinct auto-ignition modes is computed using a predictive criterion and found to be consistent with front speed and Damkohler number analyses. The hot spot study reveals that compression heating of end-gas mixture by the propagating front is more pronounced at lower mean temperatures, significantly advancing the ignition delay. Moreover, the compression heating effect is dependent on the domain size.

Characteristics of Syngas Auto-ignition at High Pressure and Low Temperature Conditions with Thermal Inhomogeneities

KAUST Repository

Pal, Pinaki

2015-05-31

Effects of thermal inhomogeneities on syngas auto-ignition at high-pressure low-temperature conditions, relevant to gas turbine operation, are investigated using detailed one-dimensional numerical simulations. Parametric tests are carried out for a range of thermodynamic conditions (T = 890-1100 K, P = 3-20 atm) and composition (Ф = 0.1, 0.5). Effects of global thermal gradients and localized thermal hot spots are studied. In the presence of a thermal gradient, the propagating reaction front transitions from spontaneous ignition to deflagration mode as the initial mean temperature decreases. The critical mean temperature separating the two distinct auto-ignition modes is computed using a predictive criterion and found to be consistent with front speed and Damkohler number analyses. The hot spot study reveals that compression heating of end-gas mixture by the propagating front is more pronounced at lower mean temperatures, significantly advancing the ignition delay. Moreover, the compression heating effect is dependent on the domain size.

Finite time synchronization of memristor-based Cohen-Grossberg neural networks with mixed delays

Science.gov (United States)

2017-01-01

Finite time synchronization, which means synchronization can be achieved in a settling time, is desirable in some practical applications. However, most of the published results on finite time synchronization don’t include delays or only include discrete delays. In view of the fact that distributed delays inevitably exist in neural networks, this paper aims to investigate the finite time synchronization of memristor-based Cohen-Grossberg neural networks (MCGNNs) with both discrete delay and distributed delay (mixed delays). By means of a simple feedback controller and novel finite time synchronization analysis methods, several new criteria are derived to ensure the finite time synchronization of MCGNNs with mixed delays. The obtained criteria are very concise and easy to verify. Numerical simulations are presented to demonstrate the effectiveness of our theoretical results. PMID:28931066

Finite time synchronization of memristor-based Cohen-Grossberg neural networks with mixed delays.

Science.gov (United States)

Chen, Chuan; Li, Lixiang; Peng, Haipeng; Yang, Yixian

2017-01-01

Finite time synchronization, which means synchronization can be achieved in a settling time, is desirable in some practical applications. However, most of the published results on finite time synchronization don't include delays or only include discrete delays. In view of the fact that distributed delays inevitably exist in neural networks, this paper aims to investigate the finite time synchronization of memristor-based Cohen-Grossberg neural networks (MCGNNs) with both discrete delay and distributed delay (mixed delays). By means of a simple feedback controller and novel finite time synchronization analysis methods, several new criteria are derived to ensure the finite time synchronization of MCGNNs with mixed delays. The obtained criteria are very concise and easy to verify. Numerical simulations are presented to demonstrate the effectiveness of our theoretical results.

Finite time synchronization of memristor-based Cohen-Grossberg neural networks with mixed delays.

Directory of Open Access Journals (Sweden)

Chuan Chen

Full Text Available Finite time synchronization, which means synchronization can be achieved in a settling time, is desirable in some practical applications. However, most of the published results on finite time synchronization don't include delays or only include discrete delays. In view of the fact that distributed delays inevitably exist in neural networks, this paper aims to investigate the finite time synchronization of memristor-based Cohen-Grossberg neural networks (MCGNNs with both discrete delay and distributed delay (mixed delays. By means of a simple feedback controller and novel finite time synchronization analysis methods, several new criteria are derived to ensure the finite time synchronization of MCGNNs with mixed delays. The obtained criteria are very concise and easy to verify. Numerical simulations are presented to demonstrate the effectiveness of our theoretical results.

How many segments are necessary to characterize delayed colonic transit time?

Science.gov (United States)

Bouchoucha, Michel; Devroede, Ghislain; Bon, Cyriaque; Raynaud, Jean-Jacques; Bejou, Bakhtiar; Benamouzig, Robert

2015-10-01

Measuring colonic transit time with radiopaque markers is simple, inexpensive, and very useful in constipated patients. Yet, the algorithm used to identify colonic segments is subjective, rather than founded on prior experimentation. The aim of the present study is to describe a rational way to determine the colonic partition in the measurement of colonic transit time. Colonic transit time was measured in seven segments: ascending colon, hepatic flexure, right and left transverse colon, splenic flexure, descending colon, and rectosigmoid in 852 patients with functional bowel and anorectal disorders. An unsupervised algorithm for modeling Gaussian mixtures served to estimate the number of subgroups from this oversegmented colonic transit time. After that, we performed a k-means clustering that separated the observations into homogenous groups of patients according to their oversegmented colonic transit time. The Gaussian mixture followed by the k-means clustering defined 4 populations of patients: "normal and fast transit" (n = 548) and three groups of patients with delayed colonic transit time "right delay" (n = 82) in which transit is delayed in the right part of the colon, "left delay" (n = 87) with transit delayed in the left part of colon and "outlet constipation" (n = 135) for patients with transit delayed in the terminal intestine. Only 3.7 % of patients were "erroneously" classified in the 4 groups recognized by clustering. This unsupervised analysis of segmental colonic transit time shows that the classical division of the colon and the rectum into three segments is sufficient to characterize delayed segmental colonic transit time.

A Fast Time-Delay Calculation Method in Through-Wall-Radar Detection Scenario

Directory of Open Access Journals (Sweden)

Zhang Qi

2016-01-01

Full Text Available In TWR (Through Wall Radar signal processing procedure, time delay estimation is one of the key steps in target localization and high resolution imaging. In time domain imaging procedure such as back projection imaging algorithm, round trip propagation time delay at the path of “transmitter-target-receiver” needs to be calculated for each pixel in imaging region. In typical TWR scenario, transmitter and receiver are at one side and targets at the other side of a wall. Based on two-dimensional searching algorithm or solving two variables equation of four times, traditional time delay calculation algorithms are complex and time consuming, and cannot be used to real-time imaging procedure. In this paper, a new fast time-delay (FTD algorithm is presented. Because of that incident angle at one side equals to refracting angle at the other side, an equation of lateral distance through the wall can be established. By solving this equation, the lateral distance can be obtained and total propagation time delay can be calculated subsequently. Through processing simulation data, the result shows that new algorithm can be applied effectively to real-time time-delay calculation in TWR signal processing.

Relativistic time delays in the Dirac approach to nucleon-nucleus scattering

International Nuclear Information System (INIS)

Suzuki, T.

1993-01-01

In connection with a characteristic feature of the effective optical potential in the Dirac approach two types of time delays are considered in the relativistic eikonal approximation. One is obtained from the scattering amplitude and the other given by the wave packet motion in the interaction region. These time delays turn out to differ in sign at intermediate energies, in contrast to the agreement between corresponding nonrelativistic time delays. (orig.)

Delay-Range-Dependent H∞ Control for Automatic Mooring Positioning System with Time-Varying Input Delay

Directory of Open Access Journals (Sweden)

Xiaoyu Su

2014-01-01

Full Text Available Aiming at the economy and security of the positioning system in semi-submersible platform, the paper presents a new scheme based on the mooring line switching strategy. Considering the input delay in switching process, H∞ control with time-varying input delay is designed to calculate the control forces to resist disturbing forces. In order to reduce the conservativeness, the information of the lower bound of delay is taken into account, and a Lyapunov function which contains the range of delay is constructed. Besides, the input constraint is considered to avoid breakage of mooring lines. The sufficient conditions for delay-range-dependent stabilization are derived in terms of LMI, and the controller is also obtained. The effectiveness of the proposed approach is illustrated by a realistic design example.

Firing patterns transition and desynchronization induced by time delay in neural networks

Science.gov (United States)

Huang, Shoufang; Zhang, Jiqian; Wang, Maosheng; Hu, Chin-Kun

2018-06-01

We used the Hindmarsh-Rose (HR) model (Hindmarsh and Rose, 1984) to study the effect of time delay on the transition of firing behaviors and desynchronization in neural networks. As time delay is increased, neural networks exhibit diversity of firing behaviors, including regular spiking or bursting and firing patterns transitions (FPTs). Meanwhile, the desynchronization of firing and unstable bursting with decreasing amplitude in neural system, are also increasingly enhanced with the increase of time delay. Furthermore, we also studied the effect of coupling strength and network randomness on these phenomena. Our results imply that time delays can induce transition and desynchronization of firing behaviors in neural networks. These findings provide new insight into the role of time delay in the firing activities of neural networks, and can help to better understand the firing phenomena in complex systems of neural networks. A possible mechanism in brain that can cause the increase of time delay is discussed.

Time delay induced different synchronization patterns in repulsively coupled chaotic oscillators

Science.gov (United States)

Yao, Chenggui; Yi, Ming; Shuai, Jianwei

2013-09-01

Time delayed coupling plays a crucial role in determining the system's dynamics. We here report that the time delay induces transition from the asynchronous state to the complete synchronization (CS) state in the repulsively coupled chaotic oscillators. In particular, by changing the coupling strength or time delay, various types of synchronous patterns, including CS, antiphase CS, antiphase synchronization (ANS), and phase synchronization, can be generated. In the transition regions between different synchronous patterns, bistable synchronous oscillators can be observed. Furthermore, we show that the time-delay-induced phase flip bifurcation is of key importance for the emergence of CS. All these findings may light on our understanding of neuronal synchronization and information processing in the brain.

Photonic-Enabled RF Canceller with Tunable Time-Delay Taps

Science.gov (United States)

2016-12-05

Photonic -Enabled RF Canceller with Tunable Time-Delay Taps Kenneth E. Kolodziej, Sivasubramaniam Yegnanarayanan, Bradley T. Perry MIT Lincoln...canceller design that uses photonics and a vector modulator architecture to provide a high number of canceller taps with tunable time-delays, which allow...microwave photonics , RF cancellation. I. INTRODUCTION In-Band Full-Duplex (IBFD) technologies are being consid- ered for 5th generation (5G) wireless

Experimental investigation of the auto-ignition characteristics of oxygenated reference fuel compounds

Science.gov (United States)

Walton, Stephen Michael

The increased use of biofuels presents an opportunity to improve combustion performance while simultaneously reducing greenhouse gases and pollutant emissions. This work focused on improving the fundamental understanding of the auto-ignition chemistry of oxygenated reference fuel compounds. A systematic study of the effects of ester structure on ignition chemistry was performed using the University of Michigan Rapid Compression Facility. The ignition properties of the ester compounds were investigated over a broad range of pressures (P=5-20 atm) and temperatures (T=850-1150 K) which are directly relevant to advanced combustion engine strategies. Ignition delay times for five esters were determined using the RCF. The esters were selected to systematically consider the chemical structure of the compounds. Three esters were saturated: methyl butanoate, butyl methanoate, and ethyl propanoate; and two were unsaturated: methyl crotonate and methyl trans-3-hexenoate. The unsaturated esters were more reactive than their saturated counterparts, with the largest unsaturated ester, methyl trans-3-hexenoate having the highest reactivity. Two isomers of the saturated esters, butyl methanoate and ethyl propanoate, were more reactive than the isomer methyl butanoate. The results are explained if we assume that butyl methanoate and ethyl propanoate form intermediate ring structures which decompose more rapidly than esters such as methyl butanoate, which do not form ring structures. Modeling studies of the reaction chemistry were conducted for methyl butanoate and ethyl propanoate, for which detailed mechanisms were available in the literature. The new experimental data indicated that literature rate coefficients for some of the methyl butanoate/HO2 reactions were too fast. Modifying these within the theoretical uncertainties for the reaction rates, led to excellent agreement between the model predictions and the experimental data. Comparison of the modeling results with the

Spontaneous ignition of methane-air mixtures in a wide range of pressures

NARCIS (Netherlands)

Zhukov, VP; Sechenov, VA; Starikovskii, AY

2003-01-01

The ignition delay in methane-air mixtures (phi = 0.5) within the range of temperatures of 1200-1700 K and pressures of 3-450 atm behind reflected shock waves in a shock tube is measured on the basis of emission of the electron-excited OH radical (transition A(2)Sigma(+) - X(2)Pi) at the wavelength

Fuel effects on illumination ignition delay and soot lift-off length in diesel combustion

NARCIS (Netherlands)

Frijters, P.J.M.; Vallen, R.G.M.; Somers, L.M.T.; Luijten, C.C.M.; Baert, R.S.G.; Skevis, G.

2007-01-01

Ignition behavior of different fuels is investigated by recording broadband soot luminosity at high speed (60 kHz).The tested fuels are regular low sulphur EN 590:2004 fuel, EN 14214:2003 (FAME), n-heptane and IDEA (2component surrogate fuel), all with a Cetane Index between 51 and 57. For this an

New distributions of the statistical time delay of electrical breakdown in nitrogen

International Nuclear Information System (INIS)

Markovic, V Lj; Gocic, S R; Stamenkovic, S N

2006-01-01

Two new distributions of the statistical time delay of electrical breakdown in nitrogen are reported in this paper. The Gaussian and Gauss-exponential distributions of statistical time delay have been obtained on the basis of thousands of time delay measurements on a gas tube with a plane-parallel electrode system. Distributions of the statistical time delay are theoretically founded on binomial distribution for the occurrence of initiating electrons and described by using simple analytical and numerical models. The shapes of distributions depend on the electron yields in the interelectrode space originating from residual states. It is shown that a distribution of the statistical time delay changes from exponential and Gauss-exponential to Gaussian distribution due to the influence of residual ionization

Extracting the relevant delays in time series modelling

DEFF Research Database (Denmark)

Goutte, Cyril

1997-01-01

selection, and more precisely stepwise forward selection. The method is compared to other forward selection schemes, as well as to a nonparametric tests aimed at estimating the embedding dimension of time series. The final application extends these results to the efficient estimation of FIR filters on some......In this contribution, we suggest a convenient way to use generalisation error to extract the relevant delays from a time-varying process, i.e. the delays that lead to the best prediction performance. We design a generalisation-based algorithm that takes its inspiration from traditional variable...

Discrete-Time Sliding-Mode Control of Uncertain Systems with Time-Varying Delays via Descriptor Approach

Directory of Open Access Journals (Sweden)

Maode Yan

2008-01-01

Full Text Available This paper considers the problem of robust discrete-time sliding-mode control (DT-SMC design for a class of uncertain linear systems with time-varying delays. By applying a descriptor model transformation and Moon's inequality for bounding cross terms, a delay-dependent sufficient condition for the existence of stable sliding surface is given in terms of linear matrix inequalities (LMIs. Based on this existence condition, the synthesized sliding mode controller can guarantee the sliding-mode reaching condition of the specified discrete-time sliding surface for all admissible uncertainties and time-varying delays. An illustrative example verifies the effectiveness of the proposed method.

Development of a simulation model for compression ignition engine running with ignition improved blend

Directory of Open Access Journals (Sweden)

Sudeshkumar Ponnusamy Moranahalli

2011-01-01

Full Text Available Department of Automobile Engineering, Anna University, Chennai, India. The present work describes the thermodynamic and heat transfer models used in a computer program which simulates the diesel fuel and ignition improver blend to predict the combustion and emission characteristics of a direct injection compression ignition engine fuelled with ignition improver blend using classical two zone approach. One zone consists of pure air called non burning zone and other zone consist of fuel and combustion products called burning zone. First law of thermodynamics and state equations are applied in each of the two zones to yield cylinder temperatures and cylinder pressure histories. Using the two zone combustion model the combustion parameters and the chemical equilibrium composition were determined. To validate the model an experimental investigation has been conducted on a single cylinder direct injection diesel engine fuelled with 12% by volume of 2- ethoxy ethanol blend with diesel fuel. Addition of ignition improver blend to diesel fuel decreases the exhaust smoke and increases the thermal efficiency for the power outputs. It was observed that there is a good agreement between simulated and experimental results and the proposed model requires low computational time for a complete run.

Study of the shock ignition scheme in inertial confinement fusion

International Nuclear Information System (INIS)

Lafon, M.

2011-01-01

The Shock Ignition (SI) scheme is an alternative to classical ignition schemes in Inertial Confinement Fusion. Its singularity relies on the relaxation of constraints during the compression phase and fulfilment of ignition conditions by launching a short and intense laser pulse (∼500 ps, ∼300 TW) on the pre-assembled fuel at the end of the implosion.In this thesis, it has been established that the SI process leads to a non-isobaric fuel configuration at the ignition time thus modifying the ignition criteria of Deuterium-Tritium (DT) against the conventional schemes. A gain model has been developed and gain curves have been inferred and numerically validated. This hydrodynamical modeling has demonstrated that the SI process allows higher gain and lower ignition energy threshold than conventional ignition due to the high hot spot pressure at ignition time resulting from the ignitor shock propagation.The radiative hydrodynamic CHIC code developed at the CELIA laboratory has been used to determine parametric dependences describing the optimal conditions for target design leading to ignition. These numerical studies have enlightened the potential of SI with regards to saving up laser energy, obtain high gains but also to safety margins and ignition robustness.Finally, the results of the first SI experiments performed in spherical geometry on the OMEGA laser facility (NY, USA) are presented. An interpretation of the experimental data is proposed from mono and bidimensional hydrodynamic simulations. Then, different trails are explored to account for the differences observed between experimental and numerical data and alternative solutions to improve performances are suggested. (author) [fr