A Unified Model for the Acceleration-Produced Burning Rate Augmentation of Metalized Solid Propellants

Abstract

Experiments have shown that acceleration of metalized composite propellants can affect an increased burning rate. The pressure-time trace of an accelerated propellant, which under static conditions would be neutral, exhibits a rapid increase to a maximum pressure and then decays asymptotically toward a quasi-equilibrium value. The model presented here attributes the augmented burning rate to the inertial retention of metal-metal oxide globules in pits on the propellant surface and the attendant heat transfer from the hot globules to the surface. A burning rate augmentation analysis for the initial period when the globules have near-spherical shapes predicts the burning-rate dependence on internal ballistic parameters and explains the observed transient behavior. As burning continues the globules grow and deform into irregularly shaped platelets and sheets which characterize the quasi-equilibrium period. Extending the model to include platelet shapes yields a functional relationship between burning rate, pressure level and acceleration which is validated by experiment.