Autoignition

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Andre L Oehma - One of the best experts on this subject based on the ideXlab platform.

  • influence of intermediate temperature heat release on Autoignition reactivity of single stage ignition fuels with varying octane sensitivity
    Proceedings of the Combustion Institute, 2020
    Co-Authors: Kwang Hee Yoo, Alexande K Voice, Andre L Oehma
    Abstract:

    Abstract This study investigates the effects of intermediate temperature heat release (ITHR) on Autoignition reactivity of full boiling range gasolines with different octane sensitivity through intake temperature and simulated exhaust gas recirculation (EGR) sweeps in a homogenous charge compression ignition (HCCI) engine. To isolate the ITHR effects, low temperature reactivity was suppressed through the use of high intake temperature and low intake oxygen mole fraction. For quantification of ITHR, a new method was applied to the engine data by examining the maximum value of the second derivative of heat release rate. Combustion phasing comparisons of fuels with octane sensitivity showed that fuel with less octane sensitivity became more reactive as intake temperature and simulated EGR ratio decreased, while fuel with higher octane sensitivity had a reverse trend. For all of the fuels that were tested, the amount of ITHR increased as the intake temperature and oxygen mole fraction increased. These ITHR trends, depending on octane sensitivity, were almost identical with the trends of combustion phasing, showing that ITHR significantly affects fuel Autoignition reactivity and determines octane sensitivity.

  • impact of fuel composition and intake pressure on lean Autoignition of surrogate gasoline fuels in a cfr engine
    Energy & Fuels, 2017
    Co-Authors: Vickey Kalaska, Dongil Kang, Andre L Oehma
    Abstract:

    The critical compression ratio (CCR) criterion (defined as the minimum compression ratio at which the fuel shows initial signs of Autoignition) was examined for various gasoline surrogate fuels in a motored engine. This investigation builds on the concept of CCR which is a good indicator of a fuel’s Autoignition characteristics, to study the fuel compositional effects with increasing intake manifold pressure. The blends consisted of binary and ternary mixtures of n-heptane and/or iso-octane, and a fuel of interest. These fuels of interest were higher octane components; toluene, ethanol, and iso-butanol. A lean condition (Φ = 0.25) with varying intake pressure (atmospheric to 3 bar, abs) and at a constant intake temperature of 155 °C was used to investigate the ignition behavior of all the blends. Two sets of blends consisted of varying percentages of fuels of interest, formulated to approximately have research octane numbers (RON) at 80 and 100. For comparison, neat iso-octane was selected as the represen...

  • Autoignition of pentane isomers in a spark ignition engine
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Song Cheng, Dongil Kang, Stanislav V Ohac, Yi Yang, Andre L Oehma
    Abstract:

    Abstract This paper describes a study on the Autoignition of three pentane isomers (n-, neo- and iso-pentane) in a Cooperative Fuel Research (CFR) engine operating at standard, ASTM knocking conditions. The Research Octane Numbers (RONs) of these three fuels are first measured and compared to historical data. Autoignition of pentane/air mixtures in the CFR engine are then simulated using a two-zone model with detailed chemical kinetics. Initial and boundary conditions for these kinetic simulations are systematically calibrated using engine simulation software. Two published, detailed kinetic mechanisms for these fuels are tested with a published NO sub-mechanism incorporated into them. Simulations using both of these mechanisms demonstrate Autoignition in the engine for all three pentanes, and that residual NO promotes Autoignition, as found in previous studies. Differences between these two mechanisms and the engine experiments are nonetheless observed, and these differences are consistent with those observed in simulations of published rapid compression machine (RCM) data. Comparison of the RCM and the CFR engine modelling also suggests the need for high accuracy experiments and high-fidelity models due to the significant impact that small differences in Autoignition timing can potentially produce in real engines.

  • Autoignition studies of c5 isomers in a motored engine
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Dongil Kang, Song Cheng, Stanislav V Ohac, Andre L Oehma, Yi Yang
    Abstract:

    Abstract This study explores the Autoignition characteristics of three C5 isomers, namely n -pentane, 2-methylbutane ( iso -pentane) and 2,2-dimethylpropane ( neo -pentane). These measurements are intended to enhance understanding of C5 Autoignition chemistry, and provide experimental data to guide improvements to a general hydrocarbon oxidation mechanism. To that end, the Autoignition behavior of these three C5 isomers was investigated in a modified CFR engine at an intake temperature of 120 °C and a fixed engine speed of 600 rpm to determine the critical compression ratio (CCR) at which hot ignition occurs. To find the critical compression ratio, the engine compression ratio (CR) was gradually increased to the point where CO in the engine exhaust rapidly decreased and significant high temperature heat release was observed, while holding equivalence ratio constant. Fundamental ignition behaviors such as the CCR and the calculated percentage of low temperature heat release (%LTHR) demonstrate the impact of chain length and methyl substitutions on ignition reactivity. The %LTHR shows a stronger two stage heat release for n- pentane than for neo- pentane observed at critical ignition conditions. In contrast, single stage heat release is observed for iso- pentane, leading to the weakest overall oxidation reactivity of the three isomers. Key reaction paths forming conjugate alkenes and C 5 oxygenated species control the Autoignition reactivity of n- pentane and iso- pentane within the low temperature and NTC regimes. However, neo- pentane forms no conjugate alkene due to its unique molecular structure, and instead produces iso -butene to retard its oxidation.

  • experimental investigation of the Autoignition behavior of surrogate gasoline fuels in a constant volume combustion bomb apparatus and its relevance to hcci combustion
    Energy & Fuels, 2012
    Co-Authors: Pete L Perez, Andre L Oehma
    Abstract:

    The Autoignition behavior of 21 surrogate gasoline fuels formulated with n-heptane, isooctane, methylcyclohexane, toluene, and 1-hexene using an augmented simplex-lattice mixture design was studied in an Ignition Quality Tester (IQT) and in a single-cylinder engine operating under homogeneous charge compression ignition (HCCI) conditions. The measured ignition delays were highly correlated to fuel composition, while the observed correlation between ignition delay and research (RON) and motor (MON) octane numbers was poor. The statistical modeling using canonical Scheffe polynomials indicated strong effects from n-heptane (Autoignition enhancer), toluene, and isooctane (Autoignition inhibitors), while methylcyclohexane and 1-hexene showed minor effects, acting essentially as inactive components in this system. The analysis of global burning rates showed that there was a limited correlation between burning rate and ignition delay, which suggests the possibility to control ignition delay and burning rate ind...

Chihje Sung - One of the best experts on this subject based on the ideXlab platform.

  • Autoignition of gasoline surrogates at low temperature combustion conditions
    Combustion and Flame, 2015
    Co-Authors: Goutham Kukkadapu, Kamal Kuma, Chihje Sung, Marco Mehl, William J. Pitz
    Abstract:

    Abstract Understanding the Autoignition characteristics of gasoline is essential for the development and design of advanced combustion engines based on low temperature combustion (LTC) technology. Formulation of an appropriate gasoline surrogate and advances in its comprehensive chemical kinetic model are required to model Autoignition of gasoline under LTC conditions. Ignition delays of two surrogates proposed in literature for a research grade gasoline (RD387), including a three-component mixture of iso -octane, n -heptane, and toluene and a four-component mixture with the addition of an olefin (2-pentene), were measured in this study using a rapid compression machine (RCM). The present RCM experiments focused on two fuel lean conditions in air corresponding to equivalence ratios of ϕ  = 0.3 and 0.5, at two compressed pressures of P C  = 20 bar and 40 bar in the compressed temperature range of T C  = 665–950 K. Comparison of the measured ignition delays of two gasoline surrogates with those of RD387 reported in our previous study shows that the four-component surrogate performs better in emulating the Autoignition characteristics of RD387. In addition, numerical simulations were carried out to assess the comprehensiveness of the corresponding gasoline surrogate model from Lawrence Livermore National Laboratory. The performance of the chemical kinetic model was noted to be pressure dependent, and the agreement between the experimental and simulated results was found to depend on the operating conditions. A good agreement was observed at a compressed pressure of 20 bar, while a reduced reactivity was predicted by the chemical kinetic model at 40 bar. Brute force sensitivity analysis was also conducted at varying pressures, temperatures, and equivalence ratios to identify the reactions that influence simulated ignition delay times. Finally, further studies for improving the surrogate kinetic model were discussed and suggested.

  • comparative Autoignition trends in butanol isomers at elevated pressure
    Energy & Fuels, 2013
    Co-Authors: Ya W Webe, Chihje Sung
    Abstract:

    Autoignition experiments of stoichiometric mixtures of s-, t-, and i-butanol in air have been performed using a heated rapid compression machine (RCM). At compressed pressures of 15 and 30 bar and ...

  • a comparative experimental study of the Autoignition characteristics of alternative and conventional jet fuel oxidizer mixtures
    Fuel, 2010
    Co-Authors: Kamal Kuma, Chihje Sung
    Abstract:

    Abstract Autoignition characteristics of an alternative (non-petroleum) and two conventional jet fuels are investigated and compared using a heated rapid compression machine. The alternative jet fuel studied is known as “S-8”, which is a hydrocarbon mixture rich in C 7 –C 18 linear and branched alkanes and is produced by Syntroleum via the Fischer–Tropsch process using synthesis gas derived from natural gas. Specifically, ignition delay times for S-8/oxidizer mixtures are measured at compressed charge pressures corresponding to 7, 15, and 30 bar, in the low-to-intermediate temperature region ranging from 615 to 933 K, and for equivalence ratios varying from 0.43 to 2.29. For the conditions investigated for S-8, two-stage ignition response is observed. The negative temperature coefficient (NTC) behavior of the ignition delay time, typical of higher order hydrocarbons, is also noted. Further, the dependences of both the first-stage and the overall ignition delays on parameters such as pressure, temperature, and mixture composition are reported. A comparison between the Autoignition responses obtained using S-8 and two petroleum-derived jet fuels, Jet-A and JP-8, is also conducted to establish an understanding of the relative reactivity of the three jet fuels. It is found that under the same operating conditions, while the three jet fuels share the common features of two-stage ignition characteristics and a NTC trend for ignition delays over a similar temperature range, S-8 has the shortest overall ignition delay times, followed by Jet-A and JP-8. The difference in ignition propensity signifies the effect of fuel composition and structure on Autoignition characteristics.

  • Autoignition of toluene and benzene at elevated pressures in a rapid compression machine
    Combustion and Flame, 2007
    Co-Authors: Gaurav Mittal, Chihje Sung
    Abstract:

    Abstract Autoignition of toluene and benzene is investigated in a rapid compression machine at conditions relevant to HCCI (homogeneous charge compression ignition) combustion. Experiments are conducted for homogeneous mixtures over a range of equivalence ratios at compressed pressures from 25 to 45 bar and compressed temperatures from 920 to 1100 K. Experiments varying oxygen concentration while keeping the mole fraction of toluene constant reveal a strong influence of oxygen in promoting ignition. Additional experiments varying fuel mole fraction at a fixed equivalence ratio show that ignition delay becomes shorter with increasing fuel concentration. Moreover, Autoignition of benzene shows significantly higher activation energy than that of toluene. In addition, the experimental pressure traces for toluene show behavior of heat release significantly different from the results of Davidson et al. [D.F. Davidson, B.M. Gauthier, R.K. Hanson, Proc. Combust. Inst. 30 (2005) 1175–1182]. Predictability of various detailed kinetic mechanisms is also compared. Results demonstrate that the existing mechanisms for toluene and benzene fail to predict the experimental data with respect to ignition delay and heat release. Flux analysis is further conducted to identify the dominant reaction pathways and the reactions responsible for the mismatch of experimental and simulated data.

E Mastorakos - One of the best experts on this subject based on the ideXlab platform.

  • direct numerical simulations of premixed methane flame initiation by pilot n heptane spray Autoignition
    Combustion and Flame, 2016
    Co-Authors: Elena Demosthenous, Giulio Orghesi, E Mastorakos
    Abstract:

    Abstract Autoignition of n-heptane sprays in a methane/air mixture and the subsequent methane premixed flame ignition, a constant volume configuration relevant to pilot-ignited dual fuel engines, was investigated by DNS. It was found that reducing the pilot fuel quantity, increases its Autoignition time. This is attributed to the faster disappearance of the most reactive mixture fraction (predicted from homogeneous reactor calculations) which is quite rich. Consequently, ignition of the n-heptane occurs at leaner mixtures. The premixed methane flame is eventually ignited due to heating gained by the pressure rise caused by the n-heptane oxidation, and heat and mass transfer of intermediates from the n-heptane Autoignition kernels. For large amounts of the pilot fuel, the combustion of the n-heptane results in significant adiabatic compression of the methane–air mixture. Hence the slow methane oxidation is accelerated and is further promoted by the presence of species in the oxidizer stream originating from the already ignited regions. For small amounts of the pilot fuel intermediates reach the oxidizer stream faster due to the very lean mixtures surrounding the n-heptane ignition kernels. Therefore, the premixed methane oxidation is initiated at intermediate temperatures. Depending on the amount of n-heptane, different statistical behaviour of the methane oxidation is observed when this is investigated in a reaction progress variable space. In particular for large amounts of n-heptane the methane oxidation follows roughly an Autoignition regime, whereas for small amounts of n-heptane methane oxidation is similar to a canonical premixed flame. The data can be used for validation of various turbulent combustion models for dual-fuel combustion.

  • simulations of Autoignition and laminar premixed flames in methane air mixtures diluted with hot products
    Combustion Science and Technology, 2014
    Co-Authors: Jennife A Sidey, E Mastorakos, Robe L Gordo
    Abstract:

    This article considers constant-pressure Autoignition and freely propagating premixed flames of cold methane/air mixtures mixed with equilibrium hot products at high enough dilution levels to burn within the moderate to intense low oxygen dilution (MILD) combustion regime. The analysis is meant to provide further insight on MILD regime boundaries and to identify the effect of hot products speciation. As the mass fraction of hot products in the reactants mixture increases, Autoignition occurs earlier. Species profiles show that the products/reactants mixture approximately equilibrates to a new state over a quick transient well before the main Autoignition event, but as dilution becomes very high, this equilibration transient becomes more prominent and eventually merges with the primary ignition event. The dilution level at which these two reactive zones merge corresponds well with that marking the transition into the MILD regime, as defined according to conventional criteria. Similarly, premixed flame simu...

  • experimental investigation of the effects of turbulence and mixing on Autoignition chemistry
    Flow Turbulence and Combustion, 2011
    Co-Authors: Christos N Markides, E Mastorakos
    Abstract:

    The Autoignition of acetylene, released from a finite-sized circular nozzle into a turbulent coflow of hot air confined in a pipe, has been the subject of a recent experimental study to supplement previous work for hydrogen and n-heptane. As with hydrogen and n-heptane, Autoignition appears in the form of well-defined localized spots. Quantitative information is presented concerning the effects of turbulence intensity, turbulent lengthscale and injector diameter on the location of Autoignition. The effects of these parameters on inhomogeneous Autoignition have not been investigated experimentally before. The present study establishes that increasing the bulk velocity increases the Autoignition length, as was reported for hydrogen and n-heptane. For the same turbulence intensity, the Autoignition length increases as the injector diameter increases and as the turbulent lengthscale decreases. A simultaneous decrease in turbulence intensity and increase in lengthscale causes a reduction in Autoignition length. Further, the frequency of appearance of the Autoignition spots has also been measured. It is found to increase when Autoignition occurs closer to the injector, and also at higher velocities. The observed trends are consistent with expectations arising from the dependence of the mixture fraction and the scalar dissipation rate on the geometrical and flow parameters. The data can be used for the validation of turbulent combustion models.

  • ignition of turbulent non premixed flames
    Progress in Energy and Combustion Science, 2009
    Co-Authors: E Mastorakos
    Abstract:

    Abstract The initiation of turbulent non-premixed combustion of gaseous fuels through Autoignition and through spark ignition is reviewed, motivated by the increasing relevance of these phenomena for new combustion technologies. The fundamentals of the associated turbulent-chemistry interactions are emphasized. Background information from corresponding laminar flow problems, relevant turbulent combustion modelling approaches, and the ignition of turbulent sprays are included. For both Autoignition and spark ignition, examination of the reaction zones in mixture fraction space is revealing. We review experimental and numerical data on the stochastic nature of the emergence of Autoignition kernels and of the creation of kernels and subsequent flame establishment following spark ignition, aiming to reveal the particular facet of the turbulence causing the stochasticity. In contrast to fully-fledged turbulent combustion where the effects of turbulence on the reaction are reasonably well-established, at least qualitatively, here the turbulence can cause trends that are not straightforward. Autoignition occurs usually away from stoichiometry at a “most reactive mixture fraction”, which can be approximately determined from homogeneous or laminar flow Autoignition calculations, and at locations in the turbulent flow with low scalar dissipation. Such locations may be the cores of vortices. Once Autoignition has occurred at a time that is mostly affected by the history of the conditional scalar dissipation, the relative magnitudes of convection, diffusion and reaction can affect the stabilisation height of flames in sprays or jets. Modelling efforts based on the Conditional Moment Closure, advanced flamelet approaches, and the transported PDF method seem suitable for capturing many, but not yet all, of the trends observed in DNS or experiment. Further experiments and DNS of realistic fuels and at conditions demonstrating chemical complexities must be performed to examine more fully the effects of scalar dissipation and its fluctuations on pre-ignition reaction zones. The statistics of the first appearance of Autoignition in transient problems and its connection with the mixing field must also be studied. Ignition from a localised spark has a stochastic character that depends on the mixture fraction sampled at the spark location and duration and the local scalar dissipation. The success or not of the subsequent flame depends on the development of turbulent edge or stratified flames. Only preliminary data exist on the propagation speed of such flames and on their quenching. A lot remains to be done on turbulent edge flame propagation in unreacted and partially-reacted mixtures with inhomogeneities, turbulent flame propagation in non-uniformly dispersed droplet mists, and the transient stabilisation process of recirculating flames. The nature of the flame generation process at very short timescales, i.e. before any appreciable propagation, by sparking in inhomogeneous mixtures needs also to be examined. The development of high repetition rate diagnostics, for single- and two-phase flows, and the development of modelling approaches capturing both premixed and non-premixed reaction zones in gaseous and spray combustion are necessary.

  • direct numerical simulations of Autoignition in turbulent two phase flows
    Proceedings of the Combustion Institute, 2009
    Co-Authors: P Schroll, Andrew P Wandel, E Mastorakos
    Abstract:

    Three-dimensional direct numerical simulations (DNS) were carried out to investigate the impact of evaporation of droplets on the Autoignition process under decaying turbulence. The droplets were taken as point sources and were tracked in a Lagrangian manner. Three cases with the same initial equivalenceratio but different initial droplet size were simulated and the focus was to examine the influence of the droplet evaporation process on the location of Autoignition. It was found that an increase in the initial droplet size results in an increase in the Autoignition time, that highest reaction rates always occur at a specific mixture fraction xi_MR, as in purely gaseous flows, and that changes in the initial droplet size did not affect the value of xi_MR. The conditional correlation coefficient between scalar dissipation rate and reaction rates was only mildly negative, contrary to the strongly negative values for purely gaseous autoigniting flows, possibly due to the continuous generation of mixture fraction by the droplet evaporation process that randomizes both the mixture fraction and the scalar dissipation fields.

Gautam Kalghatgi - One of the best experts on this subject based on the ideXlab platform.

  • Autoignition quality of gasoline fuels in partially premixed combustion in diesel engines
    Proceedings of the Combustion Institute; 33 pp 3015-3021 (2011), 2011
    Co-Authors: Gautam Kalghatgi, Leif Hildingsson, Andrew Harrison, Bengt Johansson
    Abstract:

    A single-cylinder diesel engine has been run on gasolines of different octane numbers and on model fuels, mixtures of iso-octane, n-heptane and toluene, at different operating conditions. The Autoignition quality of the fuel is best described by an Octane Index, OI = (1 - K) . RON + K . MON for fuels in the gasoline Autoignition range where RON and MON are, respectively, the Research and Motor Octane numbers and K is an empirical constant which is measured to be negative. Hence for a given RON, a non-paraffinic fuel, of lower MON, will have higher OI and more resistance to Autoignition. For a given operating condition, ignition delay increases non-linearly with OI and changes little over the Autoignition range of practical diesel fuels. Heat release following the Autoignition is influenced by the stratification which will increase as the time between the end of injection and start of combustion decreases and combustion phasing parameters such as Combustion Delay, the difference between the 50% burn time and the start of injection, become less correlated with fuel Autoignition quality. Higher ignition delays facilitate premixed combustion in the diesel engine. If two fuels have similar combustion phasing at the same injection timing, their emissions performance is also similar. Hence a good surrogate for gasoline in partially premixed compression ignition engines is a mixture of toluene, iso-octane and n-heptane with the same RON and MON. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved. (Less)

  • influence of Autoignition delay time characteristics of different fuels on pressure waves and knock in reciprocating engines
    Combustion and Flame, 2009
    Co-Authors: Derek Adley, Gautam Kalghatgi
    Abstract:

    Abstract The functional relationship of Autoignition delay time with temperature and pressure is employed to derive the propagation velocities of autoignitive reaction fronts for particular reactivity gradients, once Autoignition has been initiated. In the present study of a variety of premixtures, with different functional relationships, such gradients comprise fixed initial temperature gradients. The smaller is the ratio of the acoustic speed through the mixture to the localised velocity of the autoignitive front, the greater are the amplitude and frequency of the induced pressure wave. This might lead to damaging engine knock. At higher values of the ratio, the Autoignition can be benign with only small over-pressures. This approach to the effects of Autoignition is confirmed by its application to a variety of experimental studies involving: (i) Imposed temperature gradients in a rapid compression and expansion machine. (ii) Onset of knock in an engine with advancing spark timing. (iii) Development of Autoignition at a single hot spot in an engine. (iv) Autoignition fronts initiated by several hot spots. There is much diversity in the effects that can be produced by different fuels in different ranges of temperature and pressure. Higher values of autoignitive propagation speeds lead to increasingly severe engine knock. Such effects cannot always be predicted from the Research and Motor octane numbers.

  • Autoignition of toluene reference fuels at high pressures modeled with detailed chemical kinetics
    Combustion and Flame, 2007
    Co-Authors: Pehr Bjornbom, Johan C G Andrae, Roger Cracknell, Gautam Kalghatgi
    Abstract:

    Abstract A detailed chemical kinetic model for the Autoignition of toluene reference fuels (TRF) is presented. The toluene submechanism added to the Lawrence Livermore Primary Reference Fuel (PRF) mechanism was developed using recent shock tube Autoignition delay time data under conditions relevant to HCCI combustion. For two-component fuels the model was validated against recent high-pressure shock tube Autoignition delay time data for a mixture consisting of 35% n -heptane and 65% toluene by liquid volume. Important features of the Autoignition of the mixture proved to be cross-acceleration effects, where hydroperoxy radicals produced during n -heptane oxidation dramatically increased the oxidation rate of toluene compared to the case when toluene alone was oxidized. Rate constants for the reaction of benzyl and hydroperoxyl radicals previously used in the modeling of the oxidation of toluene alone were untenably high for modeling of the mixture. To model both systems it was found necessary to use a lower rate and introduce an additional branching route in the reaction between benzyl radicals and O 2 . Good agreement between experiments and predictions was found when the model was validated against shock tube Autoignition delay data for gasoline surrogate fuels consisting of mixtures of 63–69% isooctane, 14–20% toluene, and 17% n -heptane by liquid volume. Cross reactions such as hydrogen abstractions between toluene and alkyl and alkylperoxy radicals and between the PRF were introduced for completion of chemical description. They were only of small importance for modeling Autoignition delays from shock tube experiments, even at low temperatures. A single-zone engine model was used to evaluate how well the validated mechanism could capture Autoignition behavior of toluene reference fuels in a homogeneous charge compression ignition (HCCI) engine. The model could qualitatively predict the experiments, except in the case with boosted intake pressure, where the initial temperature had to be increased significantly in order to predict the point of Autoignition.

Henry J Curra - One of the best experts on this subject based on the ideXlab platform.

  • Autoignition of ethanol in a rapid compression machine
    Combustion and Flame, 2014
    Co-Authors: Gaurav Mittal, Sinead M Urke, Varun Anthony Davies, Ikash Parajuli, Wayne K Metcalfe, Henry J Curra
    Abstract:

    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.

  • Autoignition measurements and a validated kinetic model for the biodiesel surrogate methyl butanoate
    Combustion and Flame, 2008
    Co-Authors: Stephe Dooley, Henry J Curra, Joh M Simmie
    Abstract:

    Abstract The Autoignition of methyl butanoate has been studied at 1 and 4 atm in a shock tube over the temperature range 1250–1760 K at equivalence ratios of 1.5, 1.0, 0.5, and 0.25 at fuel concentrations of 1.0 and 1.5%. These measurements are complemented by Autoignition data from a rapid compression machine over the temperature range 640–949 K at compressed gas pressures of 10, 20, and 40 atm and at varying equivalence ratios of 1.0, 0.5, and 0.33 using fuel concentrations of 1.59 and 3.13%. The Autoignition of methyl butanoate is observed to follow Arrhenius-like temperature dependence over all conditions studied. These data, together with speciation data reported in the literature in a flow reactor, a jet-stirred reactor, and an opposed-flow diffusion flame, were used to produce a detailed chemical kinetic model. It was found that the model correctly simulated the effect of change in equivalence ratio, fuel fraction, and pressure for shock tube ignition delays. The agreement with rapid compression machine ignition delays is less accurate, although the qualitative agreement is reasonable. The model reproduces most speciation data with good accuracy. In addition, the important reaction pathways over each regime have been elucidated by both sensitivity and flux analyses.

  • ignition of isomers of pentane an experimental and kinetic modeling study
    Proceedings of the Combustion Institute, 2000
    Co-Authors: M Ribaucou, William J. Pitz, R Minetti, L R Soche, Henry J Curra, Charles K Westbrook
    Abstract:

    Experiments in a rapid compression machine were used to examine the influences of variations in fuel molecular structure on the Autoignition of isomers of pentane. Autoignition of stoichiometric mixtures of the three isomers of pentane were studied at compressed gas initial temperatures between 640 K and 900 K and at precompression pressures of 300 and 400 torr. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism. The results are interpreted in terms of a low-temperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Results indicate that in most cases, the reactive gases experience a two-stage Autoignition. The first stage follows a low-temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. At the highest compression temperatures achieved, little or no first-stage ignition is observed. Particular attention is given to the influence of heat transfer and the importance of regions of variable temperature within the compressed gas volume. Implications of this work on practical ignition problems are discussed.