Shock tube ignition measurements of iso-octane/air and toluene/air at high pressures

ignition delay times were measured in a shock tube for iso-octane/air and toluene/air at conditions similar to those found in homogeneous charge compression ignition (HCCI) engines. Initial reflected shock conditions spanned the following ranges: temperature 855-1269 K, pressure 14-59 atm, and equivalence ratios Phi of 0.5 and 1 in synthetic air. Ignition delay times were measured using sidewall pressure via piezo-electric transducers and confirmed with OH* and CH* emission measurements. The iso-octane ignition delay times are in excellent agreement with existing measurements by Fieweger et al. [Proc. Combust. Inst. 25 (1994) 1579; Combust. Flame 109 (1997) 599] and modeling by Ogink and Golovitchev [SAE Technical Paper Series, 2001, Paper No. 2001-01-3614]. No comparable high-pressure data exist for toluene/air, and modeling by Pitz et al. [U.S. Sections of the Combustion Institute 2nd Joint Spring Meeting, 2001, Paper 253] and Dagaut et al. [Fuel 81 (2002) 173] significantly over-predicts the toluene/air ignition delay times at Phi = 1. The large pressure range of the current measurements permits determination of the pressure dependence of ignition delay time at the temperatures and pressures of direct interest in HCCI engine simulations. Detailed examination of the pressure-time profiles shows evidence of significant pre-ignition energy release in both the iso-octane/air and toluene/air systems. Using current detailed mechanisms, the rate of this energy release is not correctly predicted either in iso-octane/air or toluene/air at temperatures above 850 K. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.