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Gaillimh, Ireland

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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