An experimental and kinetic modeling study of the ignition delay and heat release characteristics of a five component gasoline surrogate and its blends with iso-butanol within a rapid compression machine

This study investigates the performance of a five component gasoline surrogate (iso-octane, toluene, n-heptane, 1-hexene, and ethanol) in representing the ignition delay time (IDT) behavior of gasoline (reference gasoline PR5801—research octane number 95.4, motor octane number 86.6), at conditions of 675–870 K, 20 bar, and Ф = 1 (stoichiometric) within a rapid compression machine (RCM). Experimentally, the surrogate produces a good representation of the ignition behavior of the gasoline at these conditions, displaying a similar IDT profile. The influence of blending with iso-butanol on the surrogate's ignition delay behavior is also investigated, at blends from 5% to 70% of iso-butanol by volume. The surrogate continues to produce a reasonable representation of the experimental IDTs of gasoline and iso-butanol blends, except under a high degree of iso-butanol blending (50% iso-butanol), where the surrogate produced longer IDTs, particularly at temperatures below 740 K. Blends of 5% and 10% iso-butanol produce IDTs shorter than that of any other blend, including the “neat” surrogate, at temperatures of 740–770 and 830 K, respectively. Kinetic modeling of RCM IDTs is performed using CHEMKIN-PRO (Reaction Design: San Diego, CA, 2011) and a combined mechanism of the Sarathy et al. butanol isomers mechanism (Progress in Energy and Combustion Science 2014; 44: 40–102) and Lawrence Livermore National Laboratories “Gasoline Surrogate” mechanism (Proceedings of the Combustion Institute 2011; 33(1): 193–200). The model produces good IDT predictions below 740 K but overpredicts reactivity in the negative temperature coefficient region. Heat release rate analysis is conducted for experimental and modeling results to investigate low-temperature heat release (LTHR) behavior. Simulations largely fail to accurately reproduce this behavior. This analysis, combined with local OH and brute force Δhf sensitivity analyses, indicates the significance of LTHR in the determination of IDTs and provides RCM heat release rates for future model validation.