Importance of Spin Channels from Radical-Radical Reactions in Hydrogen-Oxygen Combustion Mechanisms at High Temperatures

Radical-radical reactions can generate two channels with high and low spins. In this work, ten radical-radical reactions with different spin channels and four radical-molecule reactions in hydrogen-oxygen combustion were systematically investigated from a theoretical perspective. The potential energy surface (PES) of radical-radical reactions reveals that the high- and low-spin states of the reactant are energetically degenerate and the two channels are energetically feasible. The difference in rate constants between the high- and low-spin channels gradually decreases as the temperature increases. Then, the kinetic parameters of the 14 bimolecular reactions in the hydrogen-oxygen mechanism of the University of California, San Diego (UCSD), were replaced to simulate the ignition delay time and laminar flame speed. The simulation results agree well with the available experimental findings, indicating the necessity of considering both high- and low-spin channels for kinetic simulation.