Gaillimh, Ireland
Gaillimh, Ireland

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De Vries J.,Texas A&M University | Lowry W.B.,Texas A&M University | Serinyel Z.,Combustion Chemistry Center | Curran H.J.,Combustion Chemistry Center | Petersen E.L.,Texas A&M University
Fuel | Year: 2011

Laminar flame speed measurements of dimethyl ether/air mixtures were made at 1, 5, and 10 atm with equivalence ratios ranging from 0.7 to 1.6. All experiments were performed in a large cylindrical constant-volume bomb with optical access. A new method for converting flame images into flame radii was used. Results reported in other studies were investigated, and some explanations on the disparities found are presented. A full uncertainty analysis was performed combining precision errors from data scatter with predicted systematic errors. Uncertainties ranging between 4.2% and 8.6% were found depending on the equivalence ratio and initial pressure. Experimental results agreed well with some other spherical flame experiments and counterflow flame measurements, but were found to be much lower than PIV-based stagnation flame results. Also, two spherical flame studies deviated significantly both in magnitude and trend. Critical radii and Peclet numbers, defined by the onset of rapid flame acceleration, were recorded for all high-pressure experiments. Markstein lengths were measured and showed a decreasing trend with increasing equivalence ratio. Three different methods were used to define the laminar flame thickness, and large disparities were found between them. In this study, the modeled temperature gradient method for the definition of flame thickness is preferred over other methods. Modeling was performed with the latest version of a C3 chemical kinetics mechanism. Good agreement is seen between the experimental results and the model at all pressures. Emphasis is placed in this paper on reporting experimental uncertainties, calculated density ratios, flame temperatures, and flame radii ranges used for data analysis, and the results resolve some discrepancies seen in the literature for dimethyl ether flame speeds. © 2010 Elsevier Ltd. All rights reserved.


Healy D.,Combustion Chemistry Center | Donato N.S.,Texas A&M University | Aul C.J.,Texas A&M University | Petersen E.L.,Texas A&M University | And 3 more authors.
Combustion and Flame | Year: 2010

Rapid compression machine and shock-tube ignition experiments were performed for real fuel/air isobutane mixtures at equivalence ratios of 0.3, 0.5, 1, and 2. The wide range of experimental conditions included temperatures from 590 to 1567. K at pressures of approximately 1, 10, 20, and 30. atm. These data represent the most comprehensive set of experiments currently available for isobutane oxidation and further accentuate the complementary attributes of the two techniques toward high-pressure oxidation experiments over a wide range of temperatures. The experimental results were used to validate a detailed chemical kinetic model composed of 1328 reactions involving 230 species. This mechanism has been successfully used to simulate previously published ignition delay times as well. A thorough sensitivity analysis was performed to gain further insight to the chemical processes occurring at various conditions. Additionally, useful ignition delay time correlations were developed for temperatures greater than 1025. K. Comparisons are also made with available isobutane data from the literature, as well as with 100% n-butane and 50-50% n-butane-isobutane mixtures in air that were presented by the authors in recent studies. In general, the kinetic model shows excellent agreement with the data over the wide range of conditions of the present study. © 2010 The Combustion Institute.


Darcy D.,Combustion Chemistry Center | Tobin C.J.,Combustion Chemistry Center | Yasunaga K.,Combustion Chemistry Center | Simmie J.M.,Combustion Chemistry Center | And 6 more authors.
Combustion and Flame | Year: 2012

Ignition delay times have been measured for mixtures of n-propylbenzene in air (≈21% O 2, ≈79% N 2) at equivalence ratios of 0.29, 0.48, 0.96 and 1.92 and at reflected shock pressures of 1, 10 and 30atm in a heated high-pressure shock tube over a wide temperature range (1000-1600K). The effects of reflected shock pressure and of equivalence ratio on ignition delay time were determined and common trends highlighted. Simulations were carried out using the n-propylbenzene sub-mechanism contained in an n-butylbenzene reaction mechanism available in the literature. This kinetic model was improved by including pressure dependent reactions which were not in place previously and the addition of the NUI Galway C 0-C 4 sub-mechanism. These simulations showed very good agreement with the experimental data. Additionally a comparison is made with experimental data previously obtained and published for n-butylbenzene over the same range of conditions and common trends are highlighted. © 2012 The Combustion Institute.


Darcy D.,Combustion Chemistry Center | Mehl M.,Lawrence Livermore National Laboratory | Simmie J.M.,Combustion Chemistry Center | Wurmel J.,Combustion Chemistry Center | And 4 more authors.
Proceedings of the Combustion Institute | Year: 2013

Alkyl aromatics are an important chemical class in gasoline, jet and diesel fuels. In the present work, an n-propylbenzene and n-heptane mixture is studied as a possible surrogate for large alkyl benzenes contained in diesel fuels. To evaluate it as a surrogate, ignition delay times have been measured in a heated high pressure shock tube (HPST) for a mixture of 57% n-propylbenzene/43% n-heptane in air (≈21% O2, ≈79% N2) at equivalence ratios of 0.29, 0.49, 0.98 and 1.95 and compressed pressures of 1, 10 and 30 atm over a temperature range of 1000-1600 K. The effects of reflected-shock pressure and equivalence ratio on ignition delay time were determined and common trends highlighted. A combined n-propylbenzene and n-heptane reaction mechanism was assembled and simulations of the shock tube experiments were carried out. The simulation results showed very good agreement with the experimental data for ignition delay times. Sensitivity and reaction pathway analyses have been performed to reveal the important reactions responsible for fuel oxidation under the shock tube conditions studied. It was found that at 1000 K, the main consumption pathways for n-propylbenzene are abstraction reactions on the alkyl chain, with particular selectivity to the allylic site. In comparison at 1500 K, the unimolecular decomposition of the fuel is the main consumption pathway. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.


Sarathy S.M.,Lawrence Livermore National Laboratory | Vranckx S.,RWTH Aachen | Yasunaga K.,Japan National Defense Academy | Mehl M.,Lawrence Livermore National Laboratory | And 7 more authors.
Combustion and Flame | Year: 2012

Alcohols, such as butanol, are a class of molecules that have been proposed as a bio-derived alternative or blending agent for conventional petroleum derived fuels. The structural isomer in traditional " bio-butanol" fuel is 1-butanol, but newer conversion technologies produce iso-butanol and 2-butanol as fuels. Biological pathways to higher molecular weight alcohols have also been identified. In order to better understand the combustion chemistry of linear and branched alcohols, this study presents a comprehensive chemical kinetic model for all the four isomers of butanol (e.g., 1-, 2-, iso- and tert-butanol). The proposed model includes detailed high-temperature and low-temperature reaction pathways with reaction rates assigned to describe the unique oxidation features of linear and branched alcohols. Experimental validation targets for the model include low pressure premixed flat flame species profiles obtained using molecular beam mass spectrometry (MBMS), premixed laminar flame velocity, rapid compression machine and shock tube ignition delay, and jet-stirred reactor species profiles. The agreement with these various data sets spanning a wide range of temperatures and pressures is reasonably good. The validated chemical kinetic model is used to elucidate the dominant reaction pathways at the various pressures and temperatures studied. At low-temperature conditions, the reaction of 1-hydroxybutyl with O 2 was important in controlling the reactivity of the system, and for correctly predicting C 4 aldehyde profiles in low pressure premixed flames and jet-stirred reactors. Enol-keto isomerization reactions assisted by radicals and formic acid were also found to be important in converting enols to aldehydes and ketones under certain conditions. Structural features of the four different butanol isomers leading to differences in the combustion properties of each isomer are thoroughly discussed. © 2011 The Combustion Institute.


Yasunaga K.,Combustion Chemistry Center | Simmie J.M.,Combustion Chemistry Center | Curran H.J.,Combustion Chemistry Center | Koike T.,Japan National Defense Academy | And 3 more authors.
Combustion and Flame | Year: 2011

A reaction mechanism of ethyl methyl ether (EME), methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE) for pyrolysis and oxidation have been constructed using the same method applied to di-ethyl ether (DEE) in our recent work [1]. The mechanism, comprising of 1051 reactions involving 215 species, was tested against the experimental data obtained using shock tubes with good agreement. It was found that the uni-molecular elimination reaction has a larger influence on the pyrolysis and oxidation of MTBE and ETBE compared to EME and DEE at high temperatures. The energy barrier height between reactants and transition states of molecular elimination reactions calculated by high level ab initio MO methods has revealed the difference in reactivity among the four ethers. It is also shown that ETBE or MTBE inhibit the reactivity of an equi-molar 2% mixture of hydrogen and oxygen, whereas EME and DEE do not inhibit reactivity. © 2010 The Combustion Institute.


Serinyel Z.,Combustion Chemistry Center | Chaumeix N.,French National Center for Scientific Research | Black G.,Combustion Chemistry Center | Simmie J.M.,Combustion Chemistry Center | Curran H.J.,Combustion Chemistry Center
Journal of Physical Chemistry A | Year: 2010

Shock tube ignition delay times have been measured for 3-pentanone at a reflected shock pressure of 1 atm (±2%), in the temperature range 1250-1850 K, at equivalence ratios of 0.5-2.0 for O2 mixtures in argon with fuel concentrations varying from 0.875 to 1.3125%. Laminar flame speeds have also been measured at an initial pressure of 1 atm over an equivalence ratio range. Complementary to previous studies [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z Black, G Curran, H. J Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587], laminar flame speeds of 2-butanone have also been measured, and relative reactivities of these ketones have been compared and discussed. A chemical kinetic submechanism describing the oxidation of 3-pentanone has been developed and detailed in this paper; rate constants for unimolecular fuel decomposition reactions have been treated for falloff in pressure with nine-parameter fits using the Troe Formulism. Both compounds treated in this work may be used as fuel tracers, thus further ignition delay time measurements have been carried out by adding 3-pentanone to n-heptane in order to test the effect of the blend on ignition delay timing. It was found that the autoignition characteristics of n-heptane remained unaffected in the presence of 15% 3-pentanone in the fuel, consistent with results obtained using acetone and 2-butanone [Pichon S., Black, G., Chaumeix, N., Yahyaoui, M., Simmie, J. M., Curran, H. J., Donohue, R. Combust. Flame, 2009, 156, 494-504; Serinyel, Z Black, G Curran, H. J Simmie, J. M. Combustion Sci. Tech., 2010, 182, 574-587]. © 2010 American Chemical Society.


Healy D.,Combustion Chemistry Center | Donato N.S.,Texas A&M University | Aul C.J.,Texas A&M University | Petersen E.L.,Texas A&M University | And 3 more authors.
Combustion and Flame | Year: 2010

Ignition delay time measurements were recorded at equivalence ratios of 0.3, 0.5, 1, and 2 for n-butane at pressures of approximately 1, 10, 20, 30 and 45. atm at temperatures from 690 to 1430. K in both a rapid compression machine and in a shock tube. A detailed chemical kinetic model consisting of 1328 reactions involving 230 species was constructed and used to validate the delay times. Moreover, this mechanism has been used to simulate previously published ignition delay times at atmospheric and higher pressure. Arrhenius-type ignition delay correlations were developed for temperatures greater than 1025. K which relate ignition delay time to temperature and concentration of the mixture. Furthermore, a detailed sensitivity analysis and a reaction pathway analysis were performed to give further insight to the chemistry at various conditions. When compared to existing data from the literature, the model performs quite well, and in several instances the conditions of earlier experiments were duplicated in the laboratory with overall good agreement. To the authors' knowledge, the present paper presents the most comprehensive set of ignition delay time experiments and kinetic model validation for n-butane oxidation in air. © 2010 The Combustion Institute.


Darcy D.,Combustion Chemistry Center | Nakamura H.,Combustion Chemistry Center | Nakamura H.,Tohoku University | Tobin C.J.,Combustion Chemistry Center | And 5 more authors.
Combustion and Flame | Year: 2014

This paper presents experimental data for the oxidation of two surrogates for the large alkylbenzene class of compounds contained in diesel fuels, namely n-decylbenzene. A 57:43 molar% mixture of n-propylbenzene: n-heptane in air (21% O2, 79% N2) was used in addition to a 64:36 molar% mixture of n-butylbenzene: 36% n-heptane in air. These mixtures were designed to contain a similar carbon/hydrogen ratio, molecular weight and aromatic/alkane ratio when compared to n-decylbenzene. Nominal equivalence ratios of 0.3, 0.5, 1.0 and 2.0 were used. Ignition times were measured at 1 atm in the shock tube and at pressures of 10, 30 and 50 atm in both the shock tube and in the rapid compression machine. The temperature range studied was from approximately 650-1700 K. The effects of reflected shock pressure and equivalence ratio on ignition delay time were determined and common trends highlighted. It was noted that both mixtures showed similar reactivity throughout the temperature range studied. A reaction mechanism published previously was used to simulate this data. Overall the reaction mechanism captures the experimental data reasonably successfully with a variation of approximately a factor of 2 for mixtures at 10 atm and fuel-rich and stoichiometric conditions. © 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.


Burke U.,Combustion Chemistry Center | Pitz W.J.,Lawrence Livermore National Laboratory | Curran H.J.,Combustion Chemistry Center
Combustion and Flame | Year: 2015

Tri-propylene glycol monomethyl ether (TPGME) is an important oxygenated fuel additive that can be used to reduce soot in diesel engines. However, a validated chemical kinetic model that incorporates the low- to high-temperature chemistry, needed to simulate ignition in a diesel engine is not available for TPGME. In addition, no fundamental experimental data are available that can be used to validate a TPGME mechanism. In this study, a surrogate chemical kinetic model for TPGME that includes low- and high-temperature chemistry has been developed, and shock tube ignition delay time data has been acquired for its validation at 0.25% TPGME for temperatures in the range of 980-1545. K, at pressures of 10 and 20. atm, and at equivalence ratios of ϕ=. 0.5, 1.0 and 2.0. The predictions from the model have been compared to the experimental measurements with good agreement. Under the experimental conditions investigated in the shock tube, TPGME was found to be consumed by molecular elimination reactions and also H-atom abstraction by H atoms and by OH and HO2 radicals. In performing sensitivity analyses it was found that the ignition of TPGME is most sensitive to reactions involving propene. Considering how the sensitivity analyses change with pressure, the most sensitive reactions involved H atoms at 10. atm and HO2 radicals at 20. atm. With respect to the effect of equivalence ratio, reactions involving H atoms are relatively more sensitive under fuel-rich conditions while those involving HO2 radicals are relatively more sensitive under fuel-lean conditions. Further experimental work is needed to enable validation of the model under low-temperature conditions. TPGME was compared to n-heptane which has similar ignition properties based on Cetane Number. Predictions showed that TPGME has a higher overall reactivity compared to n-heptane. In addition, TPGME is shown to produce significantly less soot precursor species when TPGME predictions are compared to n-heptane. © 2015 The Combustion Institute.

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