A comprehensive analysis of laser-induced ignition of RDX monopropellant

Abstract

A comprehensive analysis of laser-induced ignition of 1,3,5-trinitrohexahydro-s-triazine (RDX) monopropellant has been performed with consideration of detailed chemical kinetics. The model considers the transient development in the entire combustion zone, including the solid-phase, subsurface two-phase, and gas-phase regions. The formulation accommodates detailed chemical kinetics and transport phenomena in the gas phase, as well as thermal decomposition and subsequent reactions in the subsurface two-phase region. Thermodynamic phase transition and volumetric radiant energy absorption are also considered for completeness. The analysis is capable of treating the complete ignition process from surface pyrolysis to steady-state combustion, with the instantaneous burning rate and surface conditions treated as part of the solutions. Numerical experiments were conducted at atmospheric pressure in argon with CO 2 laser heat flux from 35 to 600 W/cm 2. Excellent agreement was obtained between the calculated and measured ignition delays. The propellant gasification rate increases with increasing laser intensity, which in turn shortens the ignition delay. The entire process can be divided into six stages: inert heating, thermal decomposition, occurrence of primary flame, preparation and formation of secondary flame and, finally, establishment of steady-state combustion. The major process in the primary flame is identified as the consumption of CH 2O, HONO, NO 2, H 2CN, H 2CNNO 2, and HNO. In the secondary flame, the conversion of NO and HCN to N 2, CO, H 2O, and H 2 is the key exothermic process causing ignition in the gas phase.