Gas-Phase Polyatomic Combustion Modeling Using Direct Simulation Monte Carlo

For the simulation of pyrolytic coking effects during atmospheric reentry, the kinetic pathways of methane, a common pyrolysis gas product, are investigated and implemented in the direct simulation Monte Carlo (DSMC) Simulator SPARTA. Bird’s Total Collision Energy Model is modified to allow for the treatment of polyatomic molecules with multiple vibrational degrees of freedom, and a new model for recombination reactions is implemented. The recombination model is capable of calculating reaction probability either through the use of the computed equilibrium constant or from rates in the literature. The new chemistry model has been validated for a variety of dissociation, exchange, and recombination chemistry reactions observed during pure methane combustion. A multivariate fitting procedure is utilized to reduce the observed underprediction of dissociation reactions at low temperatures. The post-reaction energy redistribution is performed under the assumption of equipartition of the remaining collisional energy and is verified along with expected equilibrium gas composition with simple reservoir simulations.