Collision enhancement in shocks and its implication on gas-phase detonations: A molecular dynamics and gas-kinetic theory study

Abstract

Conventional assumption in gas-phase detonations, where shock compression is decoupled from chemical kinetics, predicates on the shock and triple point structures being treated as perfect discontinuities. However, the shock is a region of high translational nonequilibrium three to five mean free paths in thickness. In this study, we use molecular dynamics simulations to probe Ar and N shocks focusing on the collision statistics in the shock front. Translationally superheated molecules were identified, as suggested by Zeldovich ( 248 (1979) 349–351), which raise the collision temperature and potentially enhance chemical reaction rates within and ahead of the shock front. We evaluated this reaction rate enhancement effect on stoichiometric H/O ZND detonation and found the effect to be negligible. The triple point region is observed to have a similar distribution of translationally superheated molecules. The temperature in the triple point region in Ar is substantially higher than that in N; the difference could impact detonation and deflagration-to-detonation characteristics due to diluent differences.