A shock tube study of the auto-ignition of toluene/air mixtures at high pressures

The auto-ignition of toluene/air mixtures was studied in a shock tube at temperatures of 1021-1400 K, pressures of 10-61 atm, and equivalence ratios of Φ = 1.0, 0.5, and 0.25. Ignition times were measured using endwall OH∗ emission and sidewall piezoelectric pressure measurements. The measured pressure time-histories do not show significant pre-ignition energy release, in agreement with the rapid compression machine study of Mittal and Sung [G. Mittal, C.-J. Sung, Combust. Flame 150 (2007) 355-368] and disagreement with the shock tube study of Davidson et al. [D.F. Davidson, B.M. Gauthier, R.K. Hanson, Proc. Combust. Inst. 30 (2005) 1175-1182]. Kinetic modeling predictions from three detailed mechanisms are compared. Sensitivity analysis indicates that the reaction of toluene (C6H5CH3) and the benzyl radical (C6H5CH2) with molecular oxygen are important and examination of the rate coefficients for these reactions suggests that improved rate parameters for the multi-channel C6H5CH2 + O2 reaction may improve model predictions.