On the critical diameter and hotspot combustion of a double-base propellant

Abstract

An analysis of experimental data on the critical diameter for burning of nitroglycerin-based propellant NB and on the temperature profiles in the combustion wave on a propellant sample in a heat-absorbing confinement was performed. It was demonstrated that, for cylindrical samples placed into a heat-absorbing confinement, there are two values of the critical diameter. The smallest value of the critical diameter (lower extinction limit) is associated with heat losses from the heat conduction zone and reaction zone of the condensed phase. The largest value of the critical diameter (upper extinction limit) is determined by heat losses from the condensed and gas phases. It was demonstrated that the value of the critical diameter is controlled by the maximum size of hotspots on the burning surface. For example, the mean critical diameter equals approximately twice the maximum hotspot size. Critical diameters characteristic of the range between the lower and upper limits range from a quarter to a half of the maximum hotspot size, with the process of extinction in this interval being of stochastic character.