Student: Stuart Barkley, Graduate Student in Mechanical Engineering, Iowa State University
Faculty Advisor: Travis Sippel
Microwave Plasma Control of Composite Solid Propellant
Several control strategies exist to throttle and extinguish solid propellant combustion, including pintle nozzles and electrically throttleable propellants. However, these techniques are limited in that they either can only be used with low flame temperature (low specific impulse)
propellants or are formulation specific. My research proposed is to develop an entirely new approach for throttling and extinguishment control of solid propellant flame through microwave plasma enhancement. Compared to previous techniques, it is an unobtrusive, lightweight technique that allows throttling of numerous energetic formulations without the weight, formulation-specific, and performance (flame temperature) drawbacks of currently used techniques.
Briefly, the propellant is doped with a small quantity (~3-4 wt. %) of material containing easily ionizing atoms, such as alkali earth metals (e.g. sodium in form of sodium nitrate, NaNO3). During decomposition and combustion, thermal energy provided by the propellant flame ionizes free alkali earth metal atoms, forming free electrons, which upon microwave irradiation leads to targeted energy deposition and thermal plasma formation. The expected increase of gas phase flame temperature enhances radiation heat feedback to the burning surface and improves the regression rate of the propellant. Previous experiments have shown a ~70% increase of the burning rate and a bulk flame temperature increase of 800 K during microwave enhancement at atmospheric conditions.