Preignition dynamics of RDX-based energetic materials under CO 2 laser heating

Abstract

The preignition dynamics of a series of RDX-based energetic materials were investigated experimentally using a high-power CO 2 laser ignition system. The materials tested were three formulations of RDX mixed with GAP binder and the energetic plasticizers TMETN or BTTN. All ignition tests were conducted at one atmosphere with varied amounts of ambient oxygen. The delay time based upon the onset of light emission ( t LE) decreased monotonically with the increase of incident laser energy flux ( q ̇ ″ ). In general, the slope of the t LE versus q ̇ ″ log-log plot became less steep as the oxygen concentration in the ambient gas was increased. This effect was more pronounced for the samples containing energetic plasticizers. For most test conditions, the initial appearance of luminous emission occurred in the gas phase above the sample surface; this implies that gas-phase reactions play an important role in the initial phase of laser-induced ignition of RDX-based energetic materials. Chemical analysis of gaseous products generated from the pyrolysis and ignition processes was conducted using a gas chromatograph and a GC/MSD (mass selective detector). Five different gas-phase zones were observed during the ignition interval: a primary reaction zone close to the sample surface, the first preparation zone, a secondary reaction zone, the second preparation zone, and the final luminous flame zone. Gas analysis showed that the products of the secondary reaction zone were NO, N 2O, C 2N 2, and HCN. These intermediate species were consumed in the final flame when the luminous flame was present.