Ignition and combustion characteristics of RDX-based pseudopropellants

Abstract

Burning rates, ignition delay times, temperature, and OH concentration profiles in the flame zone were determined for pure RDX and pseudopropellants containing RDX with CAB (cellulose acetate butyrate) binder having 8, 11, and 14% by weight. Deduced final flame temperatures ( T f ) at 0.45 MPa from UV/visible absorption spectroscopy measurements indicated a monotonic decrease of T f with an increase of CAB percentage from 3062 K for pure RDX to 2742 K for RDX/CAB (86/14%) as departure from stoichiometry became larger. The deduced final flame temperatures are in good agreement with equilibrium calculations. The measured burning rates of the propellants at 0.45 MPa decreased with increasing CAB content. No multistage flame structure was observed for either pure RDX or RDX/CAB pseudopropellants processed by shock-precipitation procedure. Measurements indicate that the ignition delay times increase with the increase of CAB content in pseudopropellants; this increase is partly due to the endothermic surface reactions of CAB and partly caused by the increase of specific heats of pseudopropellants by adding more CAB. The simple power-law curve-fitted to the ignition data indicated that the pure RDX sample surface is almost inert during the ignition period. During the tests, it was observed that the onset of light emission occurred in the gas phase above the sample surface; therefore, the gas-phase chemistry plays an important role in the ignition processes of RDX/CAB pseudopropellants.