A comprehensive analysis of RDX propellant combustion and ignition with two-phase subsurface reactions

A numerical analysis has been developed to study the key physicochemical processes involved in the combustion and ignition of RDX propellant. 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. The wide variety of time and length scales involved in chemical reactions and transport processes cause a numerical stiffness problem. The problem is circumvented by using a combined Newton-iteration and time-integration numerical method while the transient combustion characteristics is resolved by a time-marching scheme. Various important aspects of RDX burning characteristics of self-sustaining combustion at steady state are firstly examined over a broad range of pressure (0.5-1000 atm). Reasonably good agreement between calculated and measured burning rates as well as their pressure and temperature sensitivities is achieved. Laser-induced ignition of RDX propellant is also investigated. A temperature plateau in the dark zone has been observed in the case with heat-flux 400 W/cm{dollar}sp2{dollar} at atmosphere condition. It is also found that not only chemical process but also transport process plays an important role in the formation of the dark-zone temperature plateau. The major species in the dark zone and post-flame zone are identified. The transient processes of the overall flame structure are analyzed, and the conversion of NO and HCN to N{dollar}sb2{dollar}, CO, H{dollar}sb2{dollar}O and H{dollar}sb2{dollar} is found as the key exothermic process to achieve steady-state combustion.