Limitation of artificially elevating gaseous pressure in simulating catalytic recombination using reactive molecular dynamics method

Artificially elevating gaseous pressure is generally adopted in molecular dynamics simulation of gas-surface interaction on high-speed vehicles to improve calculation efficiency, which may result in the deviation of interaction mechanism or recombination coefficients from that at flight or ground test conditions. To reveal the influence pattern of gaseous pressure on surface catalytic recombination and find the physical basis of elevating gaseous pressure during simulation, heterogeneous catalytic reaction of dissociated oxygen atoms on α-quartz are studied. Statistical results show that the artificially elevated gaseous pressure changes the dominant elementary step from thermal desorption of adsorbed molecules to Eley-Rideal recombination. Meanwhile, variation pattern of rate coefficients with gaseous pressure is significantly different at extremely high-pressure conditions due to the occurrence of gaseous atom collision. According to the influence of gaseous pressure on rate coefficients, the microscale Knudsen number based on height of gaseous zone is defined to demonstrate the limitation of elevating gaseous pressure in molecule dynamics simulation of gas-surface interaction. This study deepens the understanding of catalytic recombination mechanisms of high-enthalpy dissociated atoms and provides a quality assurance for the application of microscale kinetic evolution results to macroscopic heat and mass transport.