A Journey from n-Heptane to Liquid Transportation Fuels. 1. The Role of the Allylic Radical and Its Related Species in Aromatic Precursor Chemistry

Abstract

The Utah normal heptane mechanism compiled from submechanisms in the literature was extended into a detailed normal decane combustion mechanism, which is a subset of the Utah surrogate mechanisms. Few species have greater impact on the concentrations of other species than the allyl radical CH2CH═CH2. Reactions involving the allyl radical and its isomers determine the concentration levels of all olefins, most higher unsaturated species, and benzene. To correctly predict the concentration of benzene, the reaction rates involving allyl-radical-related species need to be accurate and the concentration profiles of these species need to be satisfactory. Kinetic rates found in the literature are compared in the current work for various reference reactions that involve the allylic radicals. The improvements in numerical predictions of unsaturated species are achieved after a rigorous study in finding reliable reaction rates and kinetic correlations between various species. Some of these rates are adopted as the generic rates that have been used in the Utah surrogate mechanisms in previous studies. The modified mechanism is able to predict the concentration profiles of unsaturated species in n-decane and n-heptane flames with good numerical accuracy. The concentrations of these species are closely related to those of various allylic radicals, and reliable kinetics of allylic reactions are critical in predicting the concentrations of benzene and higher aromatics.