Radiative ignition and extinction dynamics of energetic solids

The role of heat transfer in radiant ignition/extinction behavior of homogeneous energetic solids has been studied computationally. A model has been developed based on simplified chemical kinetics, unsteady heat transfer processes in the solid phase, and quasi-steady heat transfer in the gas phase. The general behavior of ignition and extinction dynamics for a spatially uniform incident radiant flux has been simulated and explained in terms of unsteady heat transfer phenomena. Two critical heat flux levels for the incident radiation are identified. For fluxes between the critical values, there is an ignition corridor with upper and a lower limits on the allowable time for radiation exposure to achieve ignition. Below the lower critical flux there is no upper limit on the allowable exposure time to achieve ignition. Above the upper critical flux, stable ignition (self-sustained combustion on removal of the radiant flux) is not possible, that is, the ignition corridor becomes vanishingly small. The model explains the ignition corridor in terms of unsteady conductive, advective, and in-depth radiative heat transfer processes in the solid and quasi-steady conductive/advective processes in the gas-phase flame zone. Comparison is made with experimental data for go/no-go ignition behavior of cyclotetramethylene-tetranitramine (HMX).