THEORETICAL-STUDY OF BENZYL RADICAL REACTIVITY IN COMBUSTION SYSTEMS

It has recently been suggested that benzyl radicals may play an import ant role in stimulating spontaneous ignition, both in diesel and in pe trol engines. We examine here one of the proposed mechanisms, C6H5CH2 + HO2 --> C6H5CH2OOH --> C6H5CH2O + OH. The energies and structures o f the intermediate benzylhydroperoxide, and of the initial reactants a nd final products, were determined at the MP2/6-311G*//B3LYP/G-311G** level of theory. An estimate was made of the k(E) function for the un imolecular dissociation of C6H5CH2OOH into C6H5CH2O + OH, and thence, the relative fractions of collisions between C6H5CH2 and HO2 that lead directly to the formation of OH, as a function of temperature and pre ssure, as opposed to being stabilized to the hydroperoxide. The comput ed rate constants were then incorporated into a kinetic model in order to assess the importance of benzyl radicals in stimulating spontaneou s ignition in hydrocarbon-air mixtures.