Analysis of RDX monopropellant combustion with two-phase subsurface reactions

A comprehensive numerical analysis has been developed to study the key physicochemical processes involved in the self-sustained combustion of 1,3,5-trinitr ohexahydro-s-triazine (RDX) monopropellant. The model takes into account detailed chemical kinetics and transport phenomena in the gas phase, and thermal decomposition and subsequent reactions in the condensed phase. The formation of gas bubbles in the subsurface layer due to molecular degradation and evaporation is also included to provide a complete simulation. Various important aspects of RDX burning characteristics are systematically examined over a broad range of pressure, with special attention given to the effect of the subsurface two-phase flow on propellant deflagration. Good agreement between calculated and measured burning rates as well as their pressure and temperature sensitivities is achieved. Results of species concentrations reveal a multistage reaction mechanism in the gas phase. The temperature profile, however, exhibits a monotonic increase from the surface to the final flame zone. No evidence is obtained of the existence of a temperature plateau in the dark zone, consistent with some experimental observations of selfdeflagrating RDX flames using microthermocouple techniques. Further investigation into the gas-phase chemical kinetics is required to establish a unified understanding of RDX combustion under different operating conditions.