Modelling of vibrational nonequilibrium effects on the H2–air mixture ignition under shock wave conditions in the state-to-state and mode approximations

Abstract

Kinetics of physicochemical processes occurring during combustion of a hydrogen–air mixture initiated by a shock wave was studied using state-to-state and mode models that take into account nonequilibrium vibrational excitation of N2, O2, H2, and OH molecules. The effect of vibrational–translational relaxation on the induction time was considered: it was shown that the delay in establishing thermodynamic equilibrium between vibrational and translational degrees of freedom slows down the initiation of combustion, while the intensity of this effect depends on the temperature and pressure of the gas behind the shock front. An analysis of the peculiarities of vibrational distributions showed that populations of the lower vibrational levels of molecules in the course of chain reactions of combustion behind the shock wave are close to the Boltzmann ones. Therefore, it is sufficient to use the mode approximation. Calculations of the induction time using models of mode approximation showed a significant dependence of the results on the choice of the nonequilibrium factor model. If the nonequilibrium factors are calculated based on the summation of level rate constants of physicochemical processes, the accuracy of the mode model is not inferior to the accuracy of the state-to-state approximation.