Abstract
The contribution of pressure-sensitive interfacial reactions to the acoustic admittance of composite solid propellants has been studied experimentally and theoretically. Using a carboxy-terminated poly butadieneammonium perchlorate propellant, the effects of various coatings on the oxidizer crystals were investigated with a T-burner over a range of frequencies from 150 to 5000 cps. The results show that, of the coatings used (Kel-F 800, Hypalon 30, Viton A, and ethyl-cellulose), only the Kel-F and Viton reduced the apparent reactivity of the propellant binder-oxidizer interface sufficiently to produce a significant reduction in the maximum value of the observed acoustic admittance. These effects are consistent with the greater resistance to oxidation of Kel-F and Viton A compared to the other coating materials and the basic propellant binder. However, all of the coatings produced a significant shift in the acoustic frequency at which the maximum admittance is observed, even when burning rate changes are considered. Theoretical studies were conducted using a combustion model that incorporates the effects of pressuredependent surface reactions, pressure-dependent gas-phase heat transfer, and surface pyrolysis reactions. The predicted acoustic admittance frequency relation is characterized by three independent parameters using a perturbation approach. Parametric studies reveal that high ratios of the maximum acoustic response function to the burning rate pressure exponent are predicted when the net heat release at the propellant surface (pressure-dependent reactions plus pyrolysis reactions) is nearly zero or is exothermic. The stability of the combustion process in self-excited modes has also been considered theoretically and the stability bounds determined as a function of combustion parameters.
Published Version
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