The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Chih-jen Sung - One of the best experts on this subject based on the ideXlab platform.
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autoignition of crc diesel surrogates at low temperature combustion conditions Rapid Compression machine experiments and modeling
Combustion and Flame, 2020Co-Authors: Mengyuan Wang, Scott W Wagnon, Charles K Westbrook, William J Pitz, Kuiwen Zhang, Goutham Kukkadapu, Marco Mehl, Chih-jen SungAbstract:Abstract As federal programs require increasingly stringent engine emissions and fuel economy standards, these ambitions can only be met if next-generation combustion technology is developed focusing on high-efficiency and low-emissions engines. Recent research has indicated the need to operate engines at higher Compression ratios and with low temperature combustion (LTC) to achieve the needed gains in engine efficiency and reductions in emissions. Because there is a lack of understanding of the chemistry of diesel fuel components and their mixtures at these LTC conditions, this limits the ability to develop predictive chemical kinetic models that can be used to optimize engine combustion. The current study aims to fill in gaps in fundamental combustion data on surrogate fuel mixtures relevant to diesel fuels. Specifically, four multicomponent diesel surrogates formulated by the Coordinating Research Council (CRC) to emulate an ultra-low-sulfur research-grade #2 certification diesel fuel (CFA), namely V0a (4 components), V0b (5 components), V1 (8 components), and V2 (9 components), have been investigated in a Rapid Compression machine (RCM) through determination of total and first-stage ignition delay times. Autoignition characteristics of lean to rich fuel/O2/N2 mixtures, for the four CRC surrogates and CFA, have been measured using an RCM at LTC relevant pressures and temperatures, in the ranges of 10–20 bar and 650–1000 K, respectively. The equivalence ratios have been varied by independently changing the oxygen mole fraction and the fuel mole fraction in the test mixtures, thereby illustrating the individual effects of oxygen concentration and fuel loading on diesel autoignition. Autoignition results of these four CRC surrogates are compared among them and with those of CFA. Some degree of agreement in autoignition response between each CRC surrogate and CFA is observed, while discrepancies are also identified and discussed. In addition, a detailed chemical kinetic model for diesel surrogates has been developed and validated against these newly-acquired RCM data. This model shows reasonable agreement with the overall ignition delay time results of the current RCM experiments. Chemical kinetic analyses of the developed model were further conducted to help identify the reactions controlling the autoignition processes and the consumption of fuel components in CRC surrogates.
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Autoignition of trans -decalin, a diesel surrogate compound: Rapid Compression machine experiments and chemical kinetic modeling
Combustion and Flame, 2018Co-Authors: Mengyuan Wang, Scott W Wagnon, William J Pitz, Kuiwen Zhang, Goutham Kukkadapu, Marco Mehl, Chih-jen SungAbstract:Abstract Decahydronaphthalene (decalin), with both cis and trans isomers, is a bicyclic alkane that is found in aviation fuels, diesel fuels, and alternative fuels from tar sands and oil shales. Between the two decalin isomers, trans-decalin has a lower cetane number, is energetically more stable, and has a lower boiling point. Moreover, trans-decalin has often been chosen as a surrogate component to represent two-ring naphthenes in transportation fuels. Recognizing the importance of understanding the chemical kinetics of trans-decalin in the development of surrogate models, an experimental and modeling study has been conducted. Experimentally, the autoignition characteristics of trans-decalin were investigated using a Rapid Compression machine (RCM) by using trans-decalin/O2/N2 mixtures at compressed pressures of PC= 10–25 bar, low-to-intermediate compressed temperatures of TC= 620–895 K, and varying equivalence ratios of ϕ = 0.5, 1.0, and 2.0. These new experimental data demonstrate the effects of pressure, fuel loading, and oxygen concentration on autoignition of trans-decalin. The current RCM data of trans-decalin at lower temperatures were also found to complement well with the literature shock tube data of decalin (mixture of cis + trans) at higher temperatures. Furthermore, a chemical kinetic model for the oxidation of trans-decalin has been developed with new reaction rates and pathways, including, for the first time, a fully-detailed representation of low-temperature chemical kinetics for trans-decalin. This model shows good agreement with the overall ignition delay results of the current RCM experiments and the literature shock tube studies. Chemical kinetic analyses of the developed model were further conducted to help identify the fuel decomposition pathways and the reactions controlling the autoignition at varying conditions.
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autoignition study of 1 methylnaphthalene in a Rapid Compression machine
Energy & Fuels, 2017Co-Authors: Goutham Kukkadapu, Chih-jen SungAbstract:1-Methylnaphthalene (1-MN), also known as α-methylnaphthalene, is a substituted diaromatic hydrocarbon that is widely used as one of the representative aromatic hydrocarbons in surrogate fuels of diesel. The ignition characteristics of 1-MN have been investigated in the present study using a Rapid Compression machine (RCM) at compressed pressures of PC = 15–40 bar, low-to-intermediate compressed temperatures of TC = 837–980 K, and varying equivalence ratios of ϕ = 0.5, 1.0, and 1.5 in air. The current RCM ignition delay measurements were found to complement the existing shock tube ignition delay data in the literature. The performance of two of the latest literature chemical kinetic models in estimating the ignition characteristics of 1-MN has been assessed and discussed. In addition, reaction path analyses and brute force sensitivity analyses have been conducted to identify the important oxidation pathways of 1-MN described by the two literature models. Based on the results from these chemical kinetic an...
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on the uncertainty of temperature estimation in a Rapid Compression machine
Combustion and Flame, 2015Co-Authors: Bryan W Weber, Chih-jen Sung, Michael W RenfroAbstract:Abstract Rapid Compression machines (RCMs) have been widely used in the combustion literature to study the low-to-intermediate temperature ignition of many fuels. In a typical RCM, the pressure during and after the Compression stroke is measured. However, measurement of the temperature history in the RCM reaction chamber is challenging. Thus, the temperature is generally calculated by the isentropic relations between pressure and temperature, assuming that the adiabatic core hypothesis holds. To estimate the uncertainty in the calculated temperature, an uncertainty propagation analysis must be carried out. Our previous analyses assumed that the uncertainties of the parameters in the equation to calculate the temperature were normally distributed and independent, but these assumptions do not hold for typical RCM operating procedures. In this work, a Monte Carlo method is developed to estimate the uncertainty in the calculated temperature, while taking into account the correlation between parameters and the possibility of non-normal probability distributions. In addition, the Monte Carlo method is compared to an analysis that assumes normally distributed, independent parameters. Both analysis methods show that the magnitude of the initial pressure and the uncertainty of the initial temperature have strong influences on the magnitude of the uncertainty. Finally, the uncertainty estimation methods studied here provide a reference value for the uncertainty of the reference temperature in an RCM and can be generalized to other similar facilities.
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using Rapid Compression machines for chemical kinetics studies
Progress in Energy and Combustion Science, 2014Co-Authors: Chih-jen Sung, Henry J. CurranAbstract:Preparation of this review was supported by the Combustion Energy Frontier Research Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under Award Number E–SC0001198. CJS also wishes to acknowledge the financial support received from National Science Foundation, Department of Energy, Army Research Office, National Aeronautics and Space Administration, and Air Force Office of Scientific Research as well as from industry in supporting Rapid Compression machine research over the years
Henry J. Curran - One of the best experts on this subject based on the ideXlab platform.
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evaluation of non ideal piston stopping effects on the adiabatic core and ignition delay time simulation in Rapid Compression machines
Combustion and Flame, 2020Co-Authors: Chenglong Tang, Zuohua Huang, Meng Yang, Quande Wang, Peng Zhao, Henry J. CurranAbstract:Abstract Piston creep and rebound are two non-ideal piston stopping behaviors in the Rapid Compression machine. Compared to nominal piston stopping, piston rebound/creep will result in a smaller/bigger ‘adiabatic’ core zone volume in the reaction chamber and length/shorten the ignition delay time measurements. However, the ‘adiabatic core’ hypothesis can still be validated under these Compressions and ensures the applicability of zero-dimensional method in the model simulation.
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using Rapid Compression machines for chemical kinetics studies
Progress in Energy and Combustion Science, 2014Co-Authors: Chih-jen Sung, Henry J. CurranAbstract:Preparation of this review was supported by the Combustion Energy Frontier Research Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Basic Energy Sciences under Award Number E–SC0001198. CJS also wishes to acknowledge the financial support received from National Science Foundation, Department of Energy, Army Research Office, National Aeronautics and Space Administration, and Air Force Office of Scientific Research as well as from industry in supporting Rapid Compression machine research over the years
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an experimental and modeling study of shock tube and Rapid Compression machine ignition of n butylbenzene air mixtures
Combustion and Flame, 2014Co-Authors: Wayne K Metcalfe, Charles K Westbrook, William J Pitz, Marco Mehl, Hisashi Nakamura, Daniel Darcy, Colin J. Tobin, Henry J. CurranAbstract:Abstract In our previous work (D. Darcy, C.J. Tobin, K. Yasunaga, J.M. Simmie, J. Wurmel, W.K. Metcalfe, T. Niass, S.S. Ahmed, C.K. Westbrook, H.J. Curran, Combust. Flame 159 (2012) 2219–2232), ignition delay times of n-butylbenzene in air were measured using a shock tube over a temperature range of 980–1360 K, at reflected shock pressures of 1, 10, and 30 atm, and at equivalence ratios of 0.3, 0.5, 1.0 and 2.0. In the present study, these measurements have been extended to 50 atm and to lower temperatures using a Rapid Compression machine in the temperature range 730–1020 K, at compressed gas pressures of 10, 30 and 50 atm, over the same equivalence ratio range. Trends in ignition delay times over the wide temperature range were identified. The chemical kinetic model for n-butylbenzene, which was validated for the original shock tube data, was extended by adding low-temperature kinetics. The updated chemical kinetic model captures the general trend in reactivity of n-butylbenzene over the wide range of temperature, pressure and equivalence ratio conditions studied. Reaction flux analyses were carried out and it was found that fuel H-atom abstraction reactions forming the 4-phenylbut-4-yl radical, and its subsequent addition to molecular oxygen, is the primary source of reactivity in the low-temperature regime. High sensitivity to ignition delay time of the isomerization reactions of alkylperoxy, R O 2 ⇋ Q OOH , and peroxy-alkylhydroperoxide radicals, O 2 QOOH ⇋ carbonylhydroperoxide + O H , was also observed at low-temperatures. Comparisons are also made with experimental data obtained for n-propylbenzene over the same range of conditions and common trends are highlighted. It was found that, in general, n-butylbenzene was faster to ignite over the lower temperature range of 650–1000 K.
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a high pressure Rapid Compression machine study of n propylbenzene ignition
Combustion and Flame, 2014Co-Authors: Daniel Darcy, Wayne K Metcalfe, Marco Mehl, Hisashi Nakamura, Colin J. Tobin, W J Pitz, C K Westbrook, Henry J. CurranAbstract:Abstract This study presents new ignition delay data measured in a Rapid Compression machine over a wide range temperature, pressure and fuel/air ratio. This data is an extension of that measured previously (D. Darcy, C.J. Tobin, K. Yasunaga, J.M. Simmie, J. Wurmel, T. Niass, O. Mathieu, S.S. Ahmed, C.K. Westbrook, H.J. Curran, Combust. Flame, 159 (2012) 2219–2232.) for the oxidation of n-propylbenzene in a high-pressure shock tube. The data was obtained for equivalence ratios of 0.29, 0.48, 0.96, and 1.92, at compressed gas pressures of 10, 30 and 50 atm, and over the temperature range of 650–1000 K. Experimental data was also obtained at 50 atm for all equivalence ratios in our new heated high-pressure shock tube and this is also presented here. Comparisons between the data obtained in both the Rapid Compression machine and the shock tube facilities showed excellent agreement. A previously published chemical kinetic mechanism has been improved and a low-temperature reaction mechanism has been added to simulate ignition delay times at the lower temperature conditions of this study by adding the appropriate species and reactions including alkyl-peroxyl and hydroperoxy-alkyl radical chemistry. Special attention was given to R O 2 isomerizations and H O 2 elimination reactions involving the secondary benzylic site on n-propylbenzene to obtain good agreement with the present experimental results. In general, good agreement was obtained between the model and experiments and consistent trends were observed and these are discussed.
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the effect of diluent gases on ignition delay times in the shock tube and in the Rapid Compression machine
Combustion and Flame, 2007Co-Authors: Judith Wurmel, Henry J. Curran, E J Silke, M S O Conaire, John M SimmieAbstract:Abstract The diluent gas used in the preparation of test fuel/oxygen mixtures is inert and does not take part in the chemical reaction. However, it does have an effect on the measured ignition delay time both in Rapid Compression machines and in shock tubes—argon decelerates ignition in the RCM, but accelerates it in the shock tube under some conditions. This opposite effect is due to the times scales involved in these experimental devices. Typical ignition delay times in the RCM are in the region of 1–200 ms, while those in the shock tube are much shorter (10–1000 μs). Comparative RCM experiments and simulations for helium, argon, xenon, and nitrogen have shown extreme heat loss in the postCompression period, particularly for helium. Autoignition measurements of 2,3-dimethylpentane have highlighted a direct dependency of ignition delay time on the type of diluent used, where longer ignition delay time were recorded with argon. This increased ignition delay time is due to the extreme cooling of argon in the postCompression period. This observation was strengthened by comparative experiments with helium and argon, where the diluent effect was even stronger for helium, caused by its higher thermal conductivity. In the shock tube, the diluent effect is opposite to that in the RCM. For dilute mixtures of isooctane, calculations have predicted that mixtures with argon will ignite faster than those with nitrogen, based on the relative heat capacities of the two diluent gases. Overall, we conclude that the choice of diluent gases in experimental devices must be made with care, as ignition delay times can depend strongly on the type of diluent gas used.
Gaurav Mittal - One of the best experts on this subject based on the ideXlab platform.
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autoignition of ethanol in a Rapid Compression machine
Combustion and Flame, 2014Co-Authors: Gaurav Mittal, Sinead M Urke, Varun Anthony Davies, Ikash Parajuli, Wayne K Metcalfe, Henry J CurraAbstract:Abstract Ethanol is a renewable source of energy and significant attention has been directed to the development of a validated chemical kinetic mechanism for this fuel. The experimental data for the autoignition of ethanol in the low temperature range at elevated pressures are meager. In order to provide experimental data sets for mechanism validation at such conditions, the autoignition of homogeneous ethanol/oxidizer mixtures has been investigated in a Rapid Compression machine. Experiments cover a range of pressures (10–50 bar), temperatures (825–985 K) and equivalence ratios of 0.3–1.0. Ignition delay data are deduced from the experimental pressure traces. Under current experimental conditions of elevated pressures and low temperatures, chemistry pertaining to hydroperoxyl radicals assumes importance. A chemical kinetic mechanism that can accurately predict the autoignition characteristics of ethanol at low temperatures and elevated pressures has been developed and this mechanism is compared with other models available in the literature.
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a Rapid Compression machine with crevice containment
Combustion and Flame, 2013Co-Authors: Gaurav Mittal, Anil BhariAbstract:Abstract A Rapid Compression machine (RCM) incorporating ‘crevice containment’ is designed and fabricated. ‘Crevice containment’ maintains the advantage of suppression of piston-motion induced roll-up vortex while avoiding undesirable multi-dimensional effects of crevice. The geometry of the combustion chamber is optimized with computational fluid dynamic simulations. The designed RCM is demonstrated to provide highly reproducible experimental data at compressed gas pressures up to 100 bar. Pressure traces also reveal that ‘crevice containment’ leads to significant reduction in the post-Compression pressure drop. Further, the importance of ensuring instrumentation calibration and avoiding thermal shock of pressure sensor is highlighted to avoid systematic errors in measurements. High fidelity experiments are conducted for autoignition of hydrogen at compressed pressure of 50 bar. The experimental data is properly modeled by the kinetic mechanism from O’Conaire et al. [M. O’Conaire, H.J. Curran, J.M. Simmie, W.J. Pitz, C.K. Westbrook, Int. J. Chem. Kinet. 36 (11) (2004) 603–622] and discrepancy is noted from a recent mechanism [Z. Hong, D.F. Davidson, R.K. Hanson, Combust. Flame 158 (2011) 633–644].
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vortex formation in a Rapid Compression machine influence of physical and operating parameters
Fuel, 2012Co-Authors: Gaurav Mittal, Mandhapati Raju, Chih-jen SungAbstract:Abstract The performance of a Rapid Compression machine (RCM) with a creviced piston is assessed over a range of operating conditions through computational fluid dynamics simulations with systematic demonstration of the effects of compressed gas pressure, temperature, stroke length, and clearance on altering vortex formation and temperature homogeneity inside the reaction chamber. Simulated results show that as compressed gas pressure is reduced, the temperature homogeneity deteriorates due to the combined effect of thicker boundary layer and increased flow velocities. A further optimization of the creviced piston geometry is then required to completely suppress the roll-up vortex. Stroke length and clearance volume are also noted to significantly affect vortex formation. A basis for quantifying the extent of the roll-up vortex is suggested and the operating regime of an RCM with a creviced piston, that is free from the roll-up vortex, is delineated. This work emphasizes the importance of assessing the performance of an RCM over the associated range of operating conditions in order to obtain reliable chemical kinetics data.
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ignition delay study of moist hydrogen oxidizer mixtures using a Rapid Compression machine
International Journal of Hydrogen Energy, 2012Co-Authors: Chih-jen Sung, Yu Zhang, Gaurav MittalAbstract:Abstract Autoignition of moist hydrogen/oxidizer mixtures has been studied experimentally using a Rapid Compression machine (RCM). This work investigated the effect of water addition on ignition delays of stoichiometric hydrogen/oxidizer mixtures in the end of Compression temperature range of TC = 907–1048 K at three different end of Compression pressures viz. PC = 10 bar (1 MPa), 30 bar (3 MPa), and 70 bar (7 MPa). RCM experiments were conducted with 0%, 10%, and 40% molar percentages of water in the reactive mixture. At PC = 30 bar and 70 bar, the presence of 10% and 40% water vapor was shown to promote autoignition. However, at PC = 10 bar, water addition (10%) was seen to retard the reactivity, thereby increasing the ignition delay. Comparison with different reaction kinetic mechanisms reported in literature shows widely different results of simulated ignition delays for the temperature and pressure range studied, although most of the mechanism predictions demonstrate similar trend in ignition delay with water addition. A recent chemical kinetic mechanism, which shows good agreement with the present experiments at higher pressure but some discrepancy at lower pressure, was used for brute force sensitivity analysis in order to identify the important reactions for the dry mixtures in the temperature and pressure window investigated. An important reaction identified was further adjusted within the uncertainty limit as an attempt to improve the results from mechanism prediction for the ignition delay at low pressure (PC = 10 bar) without water addition. In addition, the modification in the reaction rate leads to good agreement between the experiment data and the mechanism prediction for the moist mixtures at varying compressed pressures.
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an aerosol Rapid Compression machine for studying energetic nanoparticle enhanced combustion of liquid fuels
Proceedings of the Combustion Institute, 2011Co-Authors: Casey Allen, Gaurav Mittal, Chih-jen Sung, Elisa ToulsonAbstract:The use of energetic nanoparticles offers a promising means of adjusting the reactivity of liquid fuels for enhanced combustion stability in next generation propulsion systems. This work outlines the development of a novel aerosol Rapid Compression machine (RCM) for studying the impact of energetic nanoparticles on reducing the ignition delay of liquid fuels, and a proof-of-concept demonstration is presented using ethanol and JP-8. Fuel droplets are generated using an ultrasonic nozzle. The seeding of 50 nm aluminum nanoparticles in the liquid fuel is achieved by using a combination of chemical surfactants in addition to mixing in an ultrasonic bath. The autoignition delay is measured for neat and nanoparticle-enhanced mixtures at compressed conditions of 772–830 K and 12–28 bar in the RCM. The results show that significant changes in the ignition delay can be observed using a low concentration (2%-weight) of energetic nanoparticles. For ethanol and JP-8, ignition delays were reduced by 32% and 50%, respectively. Measurements to verify the uniformity of aerosol dispersion in the RCM, the reproducibility of the RCM data, and a method for approximating compressed temperature are also presented.
John M Simmie - One of the best experts on this subject based on the ideXlab platform.
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the effect of diluent gases on ignition delay times in the shock tube and in the Rapid Compression machine
Combustion and Flame, 2007Co-Authors: Judith Wurmel, Henry J. Curran, E J Silke, M S O Conaire, John M SimmieAbstract:Abstract The diluent gas used in the preparation of test fuel/oxygen mixtures is inert and does not take part in the chemical reaction. However, it does have an effect on the measured ignition delay time both in Rapid Compression machines and in shock tubes—argon decelerates ignition in the RCM, but accelerates it in the shock tube under some conditions. This opposite effect is due to the times scales involved in these experimental devices. Typical ignition delay times in the RCM are in the region of 1–200 ms, while those in the shock tube are much shorter (10–1000 μs). Comparative RCM experiments and simulations for helium, argon, xenon, and nitrogen have shown extreme heat loss in the postCompression period, particularly for helium. Autoignition measurements of 2,3-dimethylpentane have highlighted a direct dependency of ignition delay time on the type of diluent used, where longer ignition delay time were recorded with argon. This increased ignition delay time is due to the extreme cooling of argon in the postCompression period. This observation was strengthened by comparative experiments with helium and argon, where the diluent effect was even stronger for helium, caused by its higher thermal conductivity. In the shock tube, the diluent effect is opposite to that in the RCM. For dilute mixtures of isooctane, calculations have predicted that mixtures with argon will ignite faster than those with nitrogen, based on the relative heat capacities of the two diluent gases. Overall, we conclude that the choice of diluent gases in experimental devices must be made with care, as ignition delay times can depend strongly on the type of diluent gas used.
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modeling and experimental investigation of methylcyclohexane ignition in a Rapid Compression machine
Proceedings of the Combustion Institute, 2007Co-Authors: William J Pitz, Charles K Westbrook, Henry J. Curran, Chitralkumar V Naik, Ni T Mhaolduin, J P Orme, John M SimmieAbstract:Abstract A new chemical kinetic reaction mechanism has been developed for the oxidation of methylcyclohexane (MCH), combining a new low temperature mechanism with a recently developed high temperature mechanism. Predictions from this kinetic model are compared with new experimentally measured ignition delay times from a Rapid Compression machine. Computed results were found to be particularly sensitive to isomerization rates of methylcyclohexylperoxy radicals. Three different methods were used to estimate rate constants for these isomerization reactions. Rate constants based on comparable alkylperoxy radical isomerizations corrected for the differences in the structure of MCH and the respective alkane, predicted ignition delay times in very poor agreement with the experimental results. The most significant drawback was the complete absence of a region of negative temperature coefficient (NTC) in the model results using this method, although a prominent NTC region was observed experimentally. Alternative estimates of the isomerization reaction rate constants, based on the results from previous experimental studies of low temperature cyclohexane oxidation, provided much better agreement with the present experiments, including the pronounced NTC behavior. The most important feature of the resulting methylcyclohexylperoxy radical isomerization reaction analysis was found to be the relative rates of isomerizations that proceed through 5-, 6-, and 7-membered transition state ring structures and their different impacts on the chain branching behavior of the overall mechanism. Theoretical implications of these results are discussed, with particular attention paid to how intramolecular H atom transfer reactions are influenced by the differences between linear alkane and cycloalkane structures.
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cfd studies of a twin piston Rapid Compression machine
Combustion and Flame, 2005Co-Authors: Judith Wurmel, John M SimmieAbstract:Abstract A transient 2-dimensional moving mesh CFD computer model was created, validated against experimental data, and used to investigate the flow and resulting temperature fields in a Rapid Compression machine. The sensitivity of the horizontally opposed twin-piston RCM to nonsynchronized and non-uniform piston strokes was determined and the effect of non-uniform heating on resulting pressure profiles was investigated. Predictions of the ignition temperature in a Rapid Compression machine are made very difficult due to the existence of a highly non-uniform temperature field at the end of the Compression stroke. An optimally designed piston head crevice, determined by a number of criteria, can largely overcome this problem by eliminating the mixing of the cool boundary layer gas with the hot compressed core gas. We used the CFD model to optimize the piston head crevices for our RCM and determined some new factors that are important when optimizing the piston head crevice design. Our best crevice design was then applied to a range of test gases and recommendations regarding the use of these as bath gases were made.
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the influence of fuel structure on combustion as demonstrated by the isomers of heptane a Rapid Compression machine study
Proceedings of the Combustion Institute, 2005Co-Authors: E J Silke, Henry J. Curran, John M SimmieAbstract:Abstract A detailed experimental study of the nine isomers of heptane has been performed in a Rapid Compression machine. Our interest lies in determining the role of molecular structure of the C 7 H 16 hydrocarbons on the rate of combustion of the various isomers. Ignition delay times were measured, and their dependence on the reaction conditions of temperature and pressure was studied, and in this way comparative reactivity profiles of the different isomers were obtained. Stoichiometric fuel and ‘air’ mixtures were studied in each case, at compressed gas pressure of 10, 15, and 20 atm for the n -heptane study, and at 15 atm for all other isomers, in the compressed gas temperature range of 640–960 K. Characteristic negative temperature coefficient behaviour was observed for each of the isomers. The more branched isomeric forms of heptane exhibited reduced reactivity, which correlated with the research octane number. In addition, the influence of fuel structure on burn rate was also studied. It was found that, similar to overall reactivity, the burn rate decreased with increasing octane number.
Tonghun Lee - One of the best experts on this subject based on the ideXlab platform.
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low temperature autoignition of conventional jet fuels and surrogate jet fuels with targeted properties in a Rapid Compression machine
Proceedings of the Combustion Institute, 2017Co-Authors: Daniel Valco, Tim Edwards, Kyungwook Min, Anna Oldani, Tonghun LeeAbstract:Abstract The autoignition characteristics of conventional jet fuels (category A) and alternative fuels with targeted properties (category C) are investigated using a Rapid Compression machine and the direct test chamber charge preparation approach. The category C fuels were purposefully built to anticipate special property variations that generally occur in alternative fuels. Ignition delay measurements were made to examine the effects of these unique fuels at low compressed temperatures (625 K ≤ T c ≤ 735 K), a compressed pressure of P c = 20 bar and equivalence ratios of ϕ = 0.25, 0.5 and 1.0 in synthetic dry air. Chemical makeup of the fuel shows insight into the effect of the amount of branching in isoalkanes and aromatic influences on autoignition. The results show noteworthy variability in the ignition properties at these low temperature and lean conditions. This variability may impact combustion performance when the engine is running outside the normal operational map or for new engine architectures in the future.
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low temperature autoignition behavior of surrogate jet fuels with targeted properties in a Rapid Compression machine
54th AIAA Aerospace Sciences Meeting 2016, 2016Co-Authors: Daniel Valco, Kyungwook Min, Anna Oldani, James T Edwards, Tonghun LeeAbstract:A Rapid Compression machine is used to study the autoignition characteristics of surrogate jet fuels with unique physical and/or chemical characteristics that may have an impact on the combustion properties. These surrogate fuels were specifically designed to study of the influence of chemical composition on autoignition, including the influence of branching in isoparaffins and effects of aromatic structures. The tests were conducted via a Rapid Compression machine that employed the direct test chamber charge preparation method which allows for high reproducibility of measurements. Ignition delay measurements are compared between the conventional military jet fuel and neat surrogate jet fuels. Measurements were made at a compressed pressure of 20 bar at equivalence ratios of 1.0, 0.5, and 0.25 in the low temperature region (625 K and 735 K). The results show significant variability in the ignition properties at these low temperature conditions based on the chemical structure. This variability may require attention when the engine is running outside the normal operational map or for new engine architectures in the future.
