Collisional-radiative modeling of nonequilibrium radiation in nitrogen plasma using adiabatic reactors

Fundamental research on nonequilibrium radiation in nitrogen plasma has attracted considerable attention in recent decades. In this study, we disregard fluid–radiation coupling and employ adiabatic reactors to investigate nonequilibrium radiation under both excitation and de-excitation scenarios. Validation against EAST shock tube data shows that our collisional–radiative (CR) model achieves better agreement than the two-temperature model. Radiation is predicted using both a non-Boltzmann CR model (CR-NB) and a CR model based on Boltzmann-fitted internal energy distributions (CR-Boltz). Radiation overshoots are observed in all cases and are attributed to non-Boltzmann distributions. Large discrepancies between CR-NB and CR-Boltz predictions, particularly under de-excitation conditions, arise from strong non-Boltzmann behavior in N2(C3Πu), highlighting the limitations of multi-temperature models in reproducing electronic transition radiation. We further show that different radiative systems evolve distinctly, and the dominant radiation sources in the nonequilibrium region differ between excitation and de-excitation scenarios. An analysis of elementary processes contributing to the number density of N2(C3Πu) identifies the most influential mechanisms. Finally, a study of vibrational excitation in excited states reveals that vibrational temperature has only a limited effect on the evolution of nonequilibrium radiation but underscores the necessity of vibronic models for accurately reproducing radiative peaks.