Impact of microwave plasma on burning rate and aluminum agglomeration of composite solid propellant at elevated pressures

Traditional solid rocket motors lack flexibility for dynamic thrust modulation, a challenge addressed here through plasma-enhanced combustion, offering a novel approach for thrust control. This study investigates the combustion enhancement of aluminized composite solid propellants under microwave plasma excitation at elevated pressures, aiming to understand the effects of pressure, sodium nitrate doping, and microwave power on propellant combustion. Composite propellants with varying sodium nitrate content were prepared, and the microstructure was characterized using scanning electron microscopy and energy-dispersive X-ray spectrometry. A microwave plasma-assisted high-pressure combustion chamber was developed to conduct experiments, capturing the burning and agglomeration properties of the propellants. Results show that microwave plasma significantly increases the burning rate of the propellant, with enhancements reaching up to 38.2 % at 1 atm and 10.3 % at 7 MPa for propellant with 3.5 wt.% sodium nitrate doping under 1000 W microwave excitation. Notably, a 67 % reduction in agglomerate size was achieved under 7 MPa with a 1000 W microwave field. This burning rate enhancement ratio decreases and the agglomerate size reduction ratio rises with the increase of pressure. It is observed that the burning rate increases and the agglomerate size reduces with decreasing sodium nitrate doping content and raising microwave power. Furthermore, the regulation of propellant combustion by microwave field was verified by firing test of solid rocket motor. The study demonstrates that microwave plasma technology can dynamically regulate propellant combustion under high-pressure condition, offering a promising approach for intelligent energy management in solid rocket motors. The findings pave the way for further development and practical application of microwave plasma combustion enhancement technology in aerospace propulsion systems.