Propagation and extinction of benzene and alkylated benzene flames

Laminar flame speeds and extinction strain rates of benzene, n-propylbenzene, toluene, o-, m-, and p-xylene, and 1,2,4- and 1,3,5-trimethylbenzene flames were studied experimentally in the counterflow configuration under atmospheric pressure and at the elevated temperature of 353 K for the unreacted fuel-containing stream. The experimental data revealed that the aromatic fuel structure plays a critical role on flame propagation, with the laminar flame speed decreasing with an increase in methylation of benzene. Numerical simulations suggest that the aromatics flames are highly sensitive to fuel-specific chemistry and more specifically to the reaction kinetics of the first few intermediates in the oxidation process following the fuel consumption, and that the different flame propagation speeds relate strongly to radical-radical termination facilitated by benzyl or benzyl-like intermediates. The tendencies of stretch-induced extinction of non-premixed flames was found to follow a trend that is identical to the laminar flame speed, but the extinction data revealed a more discriminative effect arising from fuel-structure differences. Comparisons between kinetic model predictions and experimental data showed that there exist significant discrepancies among these models and uncertainties in the oxidation and pyrolysis kinetics of one-ring aromatics. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.