Shock tube measurements of toluene ignition times and OH concentration time histories

Abstract

Ignition delay times and OH radical concentration profiles were measured in toluene/O 2/Ar mixtures behind reflected shock waves. Initial reflected shock conditions spanned 1400–2000 K and 1.5–5.0 atm, with equivalence ratios of 0.5–1.875 and toluene concentrations of 0.025–0.5%. OH time histories were monitored using narrow-linewidth ring dye laser absorption of the well-characterized R 1 (5) line of the OH A–X (0, 0) band at 306.7 nm. Ignition time data were extracted from the OH traces and were found to compare very well with measurements using sidewall pressure. These new data are in agreement with the recent measurements of Burcat et al. [NASA TM-87312, 1986], but not with the measurements of Pitz et al. [Second Joint Meeting, US Sections of the Combustion Institute, Paper 253, 2001] or Burcat et al. [Combust. Flame 36 (1979)]. The results of this study were compared to three detailed kinetic models: Pitz et al. [Second Joint Meeting, US Sections of the Combustion Institute, Paper 253, 2001], Dagaut et al.[Phys. Chem. Chem. Phys. 4 (2002)], and Lindstedt and Maurice [Combust. Sci. Technol. 120 (1996)]. The ability of the mechanisms to predict the measured ignition time data and OH concentration profiles was analyzed. Suggestions to improve model performance have been made, and key reactions that need to be studied further have been identified. This work has yielded the first quantitative measurements of OH time histories during toluene oxidation, and hence provides a critical data set useful for evaluating and refining comprehensive mechanisms on toluene oxidation.