Steady deflagration of hmx with simple kinetics: A new modeling paradigm

A new paradigm is presented for modeling steady combustion of energetic solids, in particular HMX. A simplified chain reaction kinetic mechanism is employed. Specifically, a zero-order, high activation energy initiation/branching reaction in the condensed phase followed by a second-order, low activation energy recombination/termination reaction in the gas phase is assumed. A closed-form solution is obtained based on activation energy asymptotics in the condensed phase and the zero activation energy limit in the gas phase. Comparisons between the model and a variety of experimental observations over a wide range of pressures and initial temperatures are given to demonstrate the validity of the approach. The model provides excellent agreement with burning rate (including sensitivity to pressure and initial temperature) and temperature profile data (in particular, the gas phase), suggesting that in the realm of simplified, approximate kinetics modeling of energetic solids, the low gas phase activation energy limit is a more appropriate modeling paradigm than the classical high activation energy limit or heuristic flame sheet models. The model also indicates that the condensed phase reaction zone plays an important role in determining the deflagration rate of HMX, underscoring the need for better understanding of the chemistry in this zone.