Mechanism of steady-state burning of composite solid propellants including those with negative pressure-exponents

Abstract

The mechanism of steady-state burning of AP-based composite solid propellants has been studied by means of single-frame microphotography with self-illumination or laser-shadow for the observation of the burning samples and scanning electron microscope for the examination of extinguished combustion strands. It has been found that covering of the molten binder over the oxidizer surface is not a particular phenomenon of PU propellants in the mesa-burning region, but a general phenomenon taking place under quite extensive circumstances. The experimental results also indicated that the local covering may not result in local extinction and features of the propellant combustion in the mesa-region are quite analogous to those of pure AP crystal deflagrating in the Regime III. A new theoretical model has been further developed, in which the existence of the covering of molten binder over oxidizer surface has been taken into consideration. And in analysing the part of AP surface covered with molten binder, the condensed-phase reaction and opposed gasification of covered AP are considered. The model developed for AP-based composite solid propellants can be used to explain plateau, mesa and normal burning features and to analyse the effects of initial temperature and AP particle size on burning behaviors.