Combustion Processes in Solid Propellant Cracks

This report presents results of a study of combustion processes in solid propellant cracks. As might be expected, under moderate chamber pressurization rates (10,000 atm/s), the theoretical predictions, as well as the experimental observations, indicate that the ignition front propagates from the entrance of the crack to the tip. However, under rapid chamber pressurization rates (100,000 atm/s or higher), the tip region of the crack was observed to ignite before the arrival of the convective ignition front. (Ignition is defined here as the onset of emission of luminous light from the propellant surface with some material loss. A theoretical model has been developed to explain the tip ignition phenomena. The model considers: a one-dimensional transient heat conduction equation for the solid phase; and one-dimensional, unsteady mass and energy conservation equations for the gas phase near the crack tip. Both experimental and theoretical results indicate that the ignition delay time decreases as the pressurization rate is increased.