Kinetic barriers, rate constants and branching ratios for unimolecular reactions of methyl octanoate peroxy radicals: A computational study of a mid-sized biodiesel fuel surrogate

Towards the goal of establishing kinetic database for low-temperature combustion (T < 1000 K) of mid-sized biodiesel surrogates, the study uses quantum chemistry and statistical kinetic methods to investigate three primary unimolecular reaction pathways of methyl octanoate peroxy radicals, including dissociation, isomerization and concerted elimination. We calculate kinetic barriers and pressure-dependent rate constants at 500-1000 K. The comparison between our computed and previously estimated rate constants offers further insight into how transition state structures and molecular mechanics are correlated with reaction kinetics. In the branching ratio analysis, we investigate the proposed unimolecular reactions and factors affecting these kinetic characteristics. For the first time, the previously measured oxidation rates of methyl octanoate under the cool flame regime (560-1000 K) are computationally verified by kinetic modeling that reflects the contribution of the present submodel to an existing detailed mechanism of methyl octanoate. Consequently, the rate-of-production analysis reveals the significance of newly proposed reaction pathways.