A modified model of mode approximation for nitrogen plasma based on the state-to-state approach

摘要

This paper addresses the analysis of thermally nonequilibrium processes in nitrogen plasma initiated by fast heating of the gas in a shock wave and by its expansion in a supersonic nozzle flow. A novel model of mode approximation has been developed that treats rate constants of plasma-chemical processes and processes of vibrational-translational, electronic-translational and electronic-electronic exchange obtained via summation of level rate coefficients of elementary reaction channels for given vibrational states, while suggesting the existence of a local Boltzmann distribution over the vibrational levels in each electronic state e= X (1)Sigma(+)(g), A (3)Sigma(+)(u), B (3)Pi(g), a' (1)Sigma(-)(u), C (3)Pi(u), of the N-2 molecule. Despite the fact that this level-based mode model is much simpler than the state-to-state model, it makes it possible to reproduce with high accuracy the evolution of nonequilibrium parameters and species concentrations predicted by the accurate state-to-state model in the post-shock-front region. However, in the expanding supersonic flow, this model cannot describe properly the variation of nonequilibrium parameters and species concentrations of electronically excited N-2 molecules and N atoms. The inaccuracy rises on decreasing the initial temperature of preheated gas in the reservoir. The comprehensive analysis of different factors influencing the prediction ability of the developed level-based mode model is also reported.