Theoretical study of benzyl radical reactivity in combustion systems

Abstract

It has recently been suggested that benzyl radicals may play an important role in stimulating spontaneous ignition, both in diesel and in petrol engines. We examine here one of the proposed mechanisms. The energies and structures of the intermediate benzylhydroperoxide, and of the initial reactants and final products, were determined at the MP2/6-311G**//B3LYP/6-311G** level of theory. An estimate was made of the k(E) function for the unimolecular dissociation of into and thence, the relative fractions of collisions that lead directly to the formation of OH, as a function of temperature and pressure, as opposed to being stabilized to the hydroperoxide. The computed rate constants were then incorporated into a kinetic model in order to assess the importance of benzyl radicals in stimulating spontaneous ignition in hydrocarbon - air mixtures.