Ignition of composite propellants in a stagnation region under rapid pressure loading

Abstract

Ignition of AP-based composite solid propellants located at the tip of an inert crack wasinvestigated both experimentally and theoretically. The ignition process was observed by simultaneously using a high-speed (≈40,000 pictures/s) camera and a fast-response photodiode system. Heat flux to the propellant surface was measured with a thin-film heat-flux gage. Effects of pressurization rate, crack-gap width, and igniter flame temperature on the ignition process were studied experimentally. Experimental results indicate that the ignition-delay time decreases and the heat flux to the propellant surface increases as the pressurization rate is increased. Results of the theoretical analysis which employed separate solid-phase energy equations for fuel and oxidizer and the measured heat flux to the propellant surface are in good agreement with experimental data. The decrease in ignition delay with increasing pressurization rate is caused by enhanced heat feedback to the propellant surface at higher pressurization rates. This augmentation in heat feedback to the propellant at higher pressurization is believed to be a result of a combination of the following mechanisms: heating due to compression-wave reflection at the closed end; heat release due to burning of unreacted igniter species near the tip, behind the compression wave; and enhanced heat transfer due to recirculating hot gases near the tip.