The thermal ignition behavior of nitramine-based solid propellants

Solid propellant formulations must meet strict performance and safety requirements. The advent of nitramine-based propellants to meet these standards has necessitated greater understanding of the ignition transient. The ignition of a nitramine-based solid propellant (XM39) subjected to conductive, convective and radiative heat transfer was examined both experimentally and theoretically. The objectives were to develop small-scale tests to screen potential propellants and evaluate relationships between these ignition mechanisms. Important chemical and physical processes were identified in separate experiments. Convective and conductive experiments were performed in a shock tube. A CO;Observed location of convective ignition indicates gas-phase chemical processes are important. Ignition delay was reduced by increases in temperature, pressure and oxidizer concentration of ambient gases. An inert heating analysis of the data was inappropriate because chemical and flow effects are important. Sharp edges on the propellant surface enhance ignition through increased heat transfer. Microscopic analysis of recovered samples show the formation of a "melt" layer but its importance is unknown.;A transient, one-dimensional ignition model for XM39 was validated using radiative ignition data. The model relies on gas-phase heat release with feedback to the propellant surface. Ignition criteria was a sharp increase in gaseous CO;The model shows that conductive ignition is governed by the propellant gasification rate. Thermal boundary layer formation reduces surface heat flux; slowing the generation of gaseous decomposition species.;Several gun propellants were fractured under shock impact with subsequent heating to study vulnerability to shaped-charge jet penetration. Ignition delay times for all propellants (JA2, M30, XM39 and M43) were reduced with induced fracture. Increased convective heating to sharp edges is the most probable mechanism. The nitramine-based propellants displayed brittle fracture making them more susceptible to violent response.