Experimental and modeling study of the oxidation of n-butylbenzene

Abstract

New 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 640–960K, at pressures from 13 to 23bar, 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 980–1740K, at reflected shock pressures of 1, 10, and 30atm. 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 1100K, at atmospheric pressure, and at equivalence ratios of 0.25, 1.0, and 2.0. Slight low-temperature reactivity (below 750K) 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 10bar, in the same rapid compression machine for stoichiometric mixtures, in a plug flow reactor at 1069K and atmospheric pressure, and in a low-pressure (0.066bar) 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.