Laser-recoil combustion response of RDX

Combustion of RDX was studied under self-deflagrating and CO₂ laser-assisted conditions at atmospheric pressure in air. Steady measurements included near-surface temperature (embedded microthermocouple), melt layer thickness, and sensitivity of burning rate to initial temperature and radiant flux. Unsteady measurements of oscillatory burning rate were also obtained using the laser-recoil technique. Thermocouple data showed a relatively thick (several hundred μm) melt layer, which increased in thickness with increasing laser flux but remained at a relatively constant temperature of about 650 K. The temporally fluctuating, spatially isothermal (time-averaged) nature of the melt layer suggest that a bubbling/mixing mechanism plays an important transport role in this zone. The temperature- and radiant flux-burning rate sensitivity data show that the equivalence principle is reasonably accurate for RDX under these conditions. The response function data agree qualitatively with those of Finlinson, et al. The classical, quasisteady ZN model does not fit RDX combustion, at least at 1 atm, presumably due to conditions in the melt layer (e.g., bubble-induced mixing) which violate model assumptions. Nevertheless these unsteady combustion data should be useful for validating more comprehensive RDX combustion models.