Electromagnetic enhanced ignition of octogen explosive at subnormal temperatures: A numerical study

Abstract

The thermal decomposition and ignition of high-performance high explosives occur via a mechanism where the solid phase sublimes and the parent molecules decompose rapidly in the gas phase to form unstable and charged intermediates. These intermediates continue to react and form the final products to release energy and do work. We have observed that the presence of electromagnetic energy significantly reduces the ignition temperature of a common high explosive, and data suggest that this occurs via electromagnetic interactions with the charged gas-phase intermediates. Here, we modified the thermal decomposition kinetic expressions for octogen (High Melt eXplosive, HMX) to couple the effects of an incident microwave (MW) field. This modified kinetic model is used to investigate our previous experimental work which showed that the surface temperature at ignition of HMX powder is reduced by the MW field. The Fridman–Macheret α-model is a common approach in plasma chemistry and was incorporated into the Henson/Smilowitz HMX kinetics; this effectively reduces the activation energy (Ea) by vibronically excited charged reactive intermediates. A modified kinetic model was implemented into the COMSOL Multiphysics Software. The thermal time to ignition was validated; as a result, plasma formation reduced the surface temperature by ∼23 °C compared to thermal ignition. With a validated kinetic model that can simulate both pure thermal ignition and mixed thermal/plasma ignition, we are able to simulate our previous experimental work showing that plasma ignition reduces the surface temperature at ignition compared to thermal initiation.