Theoretical calculation of low-temperature oxidation of heptyl radicals and O2

Author: Duan, J. R., Ji, J., Ye, L. L., Meng, Q. H., Zhai, Y. T., Zhang, L. D.

Journal: Combustion and Flame

DOI:  10.1016/j.combustflame.2020.03.021

Keywords: Heptyl radicals, Low-temperature oxidation, Kinetics, Rate constant, laminar burning velocity, pressure rate rules, shock-tube, n-heptane, master equation, ignition, kinetics, alkanes, states

Abstract: 

n-Heptane, as an alternative gasoline fuel, was used for research on low-temperature oxidation in this study, where the reactions of alkyl radicals (C7H15) and O-2 play an important role. The related chemical reaction kinetics on four C7H15 radicals and O-2 were investigated. The potential energy surfaces (PESs) of C7H15O2 were obtained by the quantum chemical calculation method of CBS-QB3. The pressure- and temperature- dependence of the rate constants was also calculated by solving master equations based on Rice-Ramsperger-Kassel-Marcus theory. In this work, all possible reaction pathways in the oxidation process were considered and calculated. Formation, concerted elimination, and intramolecular H atom transfer reactions of initial product RO2 are very critical to the low-temperature combustion. For four C7H15 radicals, the energy barriers that form RO2 from the HR + O-2 association are typically zero, and barriers to subsequent reactions are different by up to 30 kcal/mol. It is most advantageous to form QOOH fromRO(2) through a six- or seven-member ring transition state. In terms of kinetic aspect, compared with the reaction of O-2 plus secondary radicals (HR2, HR3, HR4), the reaction of adding O-2 to primary radical (HR1) is less competitive at low temperatures. Moreover, the kinetic data obtained in this study will play an important role in the kinetic model of low-temperature combustion for n-heptane. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.