Dynamic effects on ignitability limits of solidpropellants subjected to radiative heating

Abstract

The dynamic response of a solid propellant to a rapidly varying radiation flux comprises a problem representative of the general class of transient responses of heterogeneous flames to rapid disturbances. In the present study, the response of double-base propellants to roughly square-wave radiation pulses is examined. It is found that, when such pulses are used to ignite propellants, they may in some cases produce a flame which persists for whatever duration the pulse persists, but which extinguishes as soon as the pulse stops. This tendency to extinction upon deradiation is found to be lessened by increased pressure or increased time interval for reducing the flux to zero. This extinction response upon deradiation is not limited to the ignition situation; it is shown experimentally that a steadily burning propellant can be extinguished by a radiation pulse of appropriate magnitude, duration, and speed of cut-off. It is proposed that this dynamic extinction behavior results from an imbalance in the heat fluxes to and from the burning surface during deradiation. A mathematical model of this phenomenon, deriving from the nonsteady burning approach of Zeldovich, is solved and shown to predict quite well the same type of behavior as that found experimentally.