Setting the post-reaction internal energies in direct simulation Monte Carlo chemistry simulations

摘要

The application of the direct simulation Monte Carlo, or DSMC, method to chemically reacting flows requires the specification of the post-reaction internal energies of the product molecules. These have generally been set to the distributions that lead to equilibrium in a non-reacting gas and they do not lead to detailed balance for reactions with finite activation energies. Detailed balance requires that the post-reaction distributions match the relevant pre-reaction distributions and it can be enforced only if the pre-reaction distributions are known. The DSMC reaction procedures that are employed in the quantum-kinetic, or Q-K, theory have been used to derive analytical expressions for the vibrationally resolved reaction rates in an equilibrium gas. The post-reaction distributions based on these expressions promote detailed balance and have been implemented in DSMC applications to binary exchange and chain reactions and also to dissociation-recombination reactions. The results from these calculations lead to equilibrium or near equilibrium. On the other hand, similar calculations that employ the traditional procedures lead to large differences between the temperatures based on the individual energy modes.