International audienceNew experimental results for the oxidation of n-butylbenzene, a component of diesel fuel, have been obtained using three different devices. A rapid compression machine has been used to measure autoignition delay times after compression at temperatures in the range 640-960 K, at pressures from 13 to 23 bar, and at equivalence ratios from 0.3 to 0.5. Results show low-temperature behavior, with the appearance of cool flames and a negative temperature coefficient (NTC) region for the richest mixtures. To investigate this reaction at higher temperatures, a shock tube has been used. The shock tube study was performed over a wide range of experimental temperatures, pressures, and equivalence ratios, with air used as the fuel diluent. The ignition temperatures were recorded over the range 980-1740 K, at reflected shock pressures of 1, 10, and 30 atm. Mixtures were investigated at equivalence ratios of 0.3, 0.5, 1.0 and 2.0 in order to determine the effects of fuel concentration on reactivity over the entire temperature range. Using a jet-stirred reactor, the formation of numerous reaction products has been followed at temperatures from 550 to 1100 K, at atmospheric pressure, and at equivalence ratios of 0.25, 1.0, and 2.0. Slight low-temperature reactivity (below 750 K) with a NTC region has been observed, especially for the leanest mixtures. A detailed chemical kinetic model has been written based on rules similar to those considered for alkanes by the system EXGAS developed at Nancy. Simulations using this model have been compared to the experimental results presented in this study, but also to results in the literature obtained in a jet-stirred reactor at 10 bar, in the same rapid compression machine for stoichiometric mixtures, in a plug flow reactor at 1069 K and atmospheric pressure, and in a low-pressure (0.066 bar) laminar premixed methane flame doped with n-butylbenzene. The observed agreement is globally better than that obtained with models from the literature. Flow rate and sensitivity analyses have revealed a preponderant role played by the addition to molecular oxygen of resonantly stabilized, 4-phenylbut-4-yl radicals
This study presents new ignition delay data recorded in a rapid compression machine over a wide range temperature, pressure and fuel/air ratio. This data is an extension of that recorded previously (D. Darcy, C.J. Tobin, K. Yasunaga, J.M. Simmie, J. Würmel, 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. Agreement between the data obtained in both the rapid compression machine and in the shock tube facilities showed excellent complementarity. A previously published chemical kinetic mechanism has been updated in attempt 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. In general, good agreement was obtained between the model and experiments and consistent trends were observed * address: Combustion Chemistry Centre, School of Chemistry, NUI Galway, Ireland. Phone: 00353-91-493856. Email: firstname.lastname@example.org URL: http://c3.nuigalway.ie/ (H.J. Curran)Preprint submitted to Combustion and Flame February 5, 2013 and these are discussed. Comparisons are also made with experimental data obtained for n-butylbenzene 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.
This paper presents experimental data for the oxidation of two surrogates for the large alkylbenzene class of compounds contained in diesel fuels, namely ndecylbenzene. A 57:43 molar % mixture of n-propylbenzene:n-heptane in air (≈21% O 2 , ≈79% N 2 ) was used in addition to a 64:36 molar % mixture of nbutylbenzene: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 * address: 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.
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