First-Principle-Inspired Reduced-Order Models of Chemical Kinetics in Hydrogen System

In the present study, two different reduced-order models are proposed for the [Formula: see text] system by leveraging first-principles quasi-classical trajectory simulations and in-depth master equation analyses. The most recent available ab initio potential energy surface is adopted to construct a new set of rovibrational state-to-state kinetic databases valid over a wide range of temperatures. First, a modified two-temperature model is proposed by incorporating the master equation-informed model parameters, enabling the advanced treatment of internal energy coupling and nonequilibrium dissociation predictions. Second, a hybrid coarse-graining model is proposed by combining a graph-based approach optimized globally for a wide range of temperatures with a centrifugal-barrier-based coarse-graining method. The proposed reduced-order models offer significantly improved accuracy in predicting nonequilibrium energy transfer and dissociation dynamics compared to the existing coarse-graining and 2T models in previous studies. In addition, aerothermal heating prediction relevant to Uranus planetary entry reveals a 16.5% discrepancy in convective heat flux compared to the present modified 2T approach with the existing 2T, demonstrating the importance of accurate modeling of chemical kinetics in the [Formula: see text] system.