Nitramine deflagration - Reduced chemical mechanism for primary flame facilitating simplified asymptotic analysis

It is proposed that nitramines burn by staged combustion in which most of the energy is released in a secondary flame that is convective-re active in character and that has a negligible influence on the deflagration velocity. A nearly adiabatic condition is then achieved at the end of the primary gas-phase flame that precedes this secondary flame, the flame temperature 7} at the adiabatic point lying between about 1200-1500 K. The detailed gas-phase chemical kinetics for this primary flame are addressed here. The chemistry is reasoned to involve initially a set of elementary steps that result in HONO, HCN, H2CO, and N2O as decomposition products obtained hi an overall endothermic manner at temperatures in the vicinity of 1000 K, followed by steps that exothermically produce NO, N2, CO2, H2O, and HOCN at a rate found through systematic reduction of the chemistry to be that of bimolecular HONO decomposition. Systematic reduction of the chemistry of the initial process enables the ratio of HCN to H 2CO to be determined as a function of pressure, thereby predicting the pressure dependence of 7} and showing that this primary flame temperature decreases gradually with increasing pressure. Because of the activation energy of HONO decomposition, this decrease causes the effective pressure exponent of the exothermic reduced step to be less than two, and thereby reproduces the experimentally observed pressure exponent of about 0.8 for the deflagration velocity. Excellent agreement is obtained with measured deflagration velocities of cyclotrimethylenetrinitramine.