Abstract
A study lias been made to relate theoretically predicted and experimentally observed pressure-coupled combustion instability behavior of solid propellants. Using a generalized theoretical model the linear and nonlinear region has been characterized by generalized combustion parameters. A comparison of the experimental data with theoretical predictions in the linear region (i.e., acoustic response functions) shows that small changes in propellant formulations can have a significant effect on the derived parameters characterizing the combustion. Analysis of the data shows that propellants having 84% solids loading are more likely to show the surface gasification to be pressure dependent than those having lower loadings; the temperature dependence of the gasification process is larger than can be explained by an Arrhenius rate expression with a reasonable activation energy; and the rate of energy transfer into the solid phase was found to increase with increasing surface temperature. This suggests the influence of exothermic surface processes. The effect of pressure on the energy transfer was found to be consistent with the several proposed models for gas-phase combustion effects. Higher order effects show that both positive and negative shifts in the time average burning rate with acoustic pressure can be obtained. Since Eisel has observed this effect to be negative, this defines the region of reasonable second order coefficients. Additional studies show that the acoustic response function can decrease with increasing acoustic pressure. Hence, the combustion process itself can limit the acoustic pressure amplitude in the T-burner.
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