Towards a predictive kinetic model of 3-ethyltoluene: Evidence concerning fuel-specific intermediates in the flow reactor pyrolysis with insights into model implications

To reveal insights into high temperature kinetics of dialkylaromatics, a pyrolysis investigation of 3ethyltoluene in a flow reactor together with its reaction kinetics are presented in this work. Concentrations and chemical structures of specific species covering temperature range from 796 to 1383K at the pressure of 30 and 760 Torr were recorded and quantified by using synchrotron vacuum ultraviolet photoionization molecular-beam mass spectrometry (VUV-PI-MBMS). Important C 8 and C 9 fuel-specific intermediates relevant to primary decomposition of 3-ethyltoluene and isomerization of methylbenzyl and ethylbenzyl radicals were detected and identified. The kinetic model interpreting high temperature pyrolysis chemistry of 3-ethyltoluene was developed and reasonably predicted the measurements in this work. The model analyses reveal that the methyl-dissociated reaction from the ethyl group of 3-ethyltoluene is dominant in the fuel decomposition at low pressure, while the fuel is mainly consumed by hydrogen abstraction reactions at atmospheric pressure. The experimental observations of three methylbenzyl isomers, o -xylylene, p -xylylene, styrene and benzocyclobutene provide evidence for the relationships between products involving isomerization of methylbenzyl radicals, formation of xylylenes and decomposition of o -xylylene. The fuel structure effects of 3-ethyltoluene and m -xylene are revealed by comparing the pyrolysis behaviors in both cases. It has been found that the m -methylbenzyl-generating channel in the 3-ethyltoluene pyrolysis improved the reaction reactivity initially. Furthermore, the fuel with longer substituent ethyl group facilitates the formation of cycloalkenes and aromatics.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved