Thermochemical Erosion of Carbon Composite Materials in Solid-Propellant Rig Tests

The effect of a gas curtain resulting from the pyrolysis of the combustion chamber internal insulation in solid-propellant gas generators on the ablation of carbon inserts in the nozzle throat is investigated. Experimental data from two series of fire tests on test rigs are analyzed: those conducted by the authors and those described in the literature. The linear ablation rates obtained in the two series of tests are 2.5 and 6 times lower, respectively, than those calculated using standard methods for large-scale solid rocket motors. A mathematical model is proposed based on the coupled solution of integral momentum and energy relations for the boundary layer and the determination of the thermal state and ablation of materials. This model accounts for additional admixtures of “cold” gas chemically inert with respect to carbon into the flow of propellant combustion products. The model is validated by comparing calculated and experimental data, which differ by no more than 5%.