Experimental investigation of boron combustion in air-augmented rockets

Studies have been made using a windowed combustion tunnel to examine the mixing and burning between subsonic air and a supersonic fuel-rich exhaust of a rocket motor burning hydrogen-oxygen-boron mixtures. The reaction processes were recorded by high-speed cinephotography. Results of experiments are presented in which the following parameters were varied: 1) boron concentration in the propellant (up to 55% by weight), 2) nonequilibrium chamber temperature of the primary rocket (750 °K to 2500 °K), and 3) air to propellant flow ratio (3 to 15). The temperature of the primary rocket was calculated by assuming boron as a heat sink. These calculations showed good agreement with experimental data at low chamber temperatures. The strong influence of the primary nonequilibrium chamber temperature on the boron combustion efficiency was demonstrated using the results of particle sampling probes and c*-efficiency measurements. By increasing the chamber temperature from 750°K to 2000°K the over-all reaction efficiency was improved from 85 to 94%.