Quasiclassical trajectory analysis of N₂ + O₂ and implications for hypersonic CFD

Modern computational fluid dynamics tools simulate gas-phase chemical kinetics using empirical models based on historical shock tube data, leading to significant uncertainty. This paper presents a review of quasiclassical trajectory analysis and how it may be used to investigate physical mechanisms and develop next-generation kinetics models. We discuss nitrogen dissociation with collision partners N₂, N and O₂, and oxygen dissociation with collision partner N₂. The QCT analysis shows that atomic nitrogen promotes the vibrational relaxation of N₂, increasing the net dissociation rate. Park1 attributes this increase exclusively to a larger dissociation rate constant of N₂ + N compared to N₂+ N₂, which we find to be incorrect. The vibrational energy removed due to dissociation, a necessary input to CFD, is found to strongly depend on the degree of thermal nonequilibrium. Finally, we define the support quantity S to assess which factors may be neglected for a reduced-order model. Using support, we show that simple dissociation is independent of the collision partner’s internal energy at thermal equilibrium for all reactions we have studied. These rigorous statistical analyses enable the development of next-generation models.