Strand size and low pressure deflagration limit in a composite propellant

Abstract

The low-pressure deflagration limit, LPDL, has been determined for a composite ammonium perchlorate propellant over a range of pressures from 35 to 235 torr. The independent variable was strand cross section area. A linear relation was found between the LPDL and the inverse of the hydraulic radius of the strand. It was thus possible to extrapolate and determine the low-pressure limit for a strand of infinite extent. It can be argued that such an infinite strand is adiabatic. A possible mechanism to explain a finite extinguishing pressure for an adiabatic strand is the lack of sufficient oxidant in the gas phase due to differences in the rate of change of fuel and oxidizer gasification rates with decreasing pressure. I. Introduction S OME time ago we attempted to examine the structure of the combustion zone above a strand of composite solid propellant by means of interferometry. In order to increase spatial resolution we expanded the zone by burning propellant strands at subatmospheri c pressure in a chamber which could be continuously pumped and which was provided with windows for observation. For reasons that we probably should have anticipated we fell somewhat short of our primary objective. In the course of our experiments, however, we did obtain some data on the low-pressure deflagration limit, LPDL, for two composite propellant compositions. In particular, we determined the dependence of LPDL on strand size. It seems in order to record these results because they may provide some grist for the theorist's mills and shed