ETC closed-vessel experiments with alkali-doped propellants

Experiments with the objective to stimulate combustion of solid propellant through addition of electric energy are reported. In this paper, the idea of stimulating combustion by conducting an electric current through the flame is tested. The current leads to resistive heating of the flame, which adds to the reaction heat, and thus amplifies the heat feedback to the unburnt propellant. The electric conductivity of the flame must be sufficiently high in order to reduce random delay and to increase controllability of the electric discharge. The propellant composition has to be modified to meet this requirement. Thermochemical calculations give the equilibrium state and composition, which are used to estimate the flame conductivity. Calculations are carried out for several propellant compositions: some being considered for preparation, while others are intended solely for comparison. The calculation results indicate that, given a high flame temperature, a substantial increase in conductivity can be obtained by doping the propellants with alkali compounds. A double-base propellant doped with potassium nitrate has been used in the experiments so far. The experiments are performed in a closed vessel where a propellant slab is pinched between two copper plates connected to a pulsed power supply. Results presented include current and voltage recordings, yielding the added electric energy, and pressure measurements from which the burn rate can be determined.