Interaction of capillary plasma with double-base and composite propellants

Experiments were conducted to characterize the electrothermal capillary plasma and its interaction with a double-base propellant, JA2, and two nitramine composite propellants, M43 and XM39, in closed-chamber and open-air conditions. Pressure-time histories were recorded during ignition and burning of the propellants in the closed chamber. Experimental results indicate significant differences in ignition and combustion of the propellants. The composite propellants exhibited a two-stage burning behavior: one stage of rapid burning driven by the plasma and a second stage of slower self-sustained burning, which occurred with a clear delay after the first stage. During the burning that is driven by the plasma, the burn rate was largely independent of propellant type. Optical microscopic images of recovered propellant samples showed clear physical changes in surface and possibly in subsurface structure, an indication of in-depth melting, vaporization, and possibly chemical reactions. Plasma-induced mass losses for the three propellants were obtained from open-air testing and compared to the values calculated based on the pressure data from closed-chamber tests.