Pulsed Microwave Plasma Instrumentation for Investigation of Plasma-Tuned Multiphase Combustion

Instrumentation developed to support the investigation of electromagnetic wave interaction with energetic materials and flames could help develop microwave-sensitive energetic materials that produce effects such as microwave ignition, acceleration of burning rate, extinguishment, and re-ignition.

Air Force Research Laboratory, Arlington, Virginia

Strategies to control solid rocket propellant regression rate require a robust throttling technique applicable to high performance propellant formulations. Currently, several methods to control and throttle either motors or subscale propellant strands exist, including chamber pressure control (e.g. pintle nozzles or rapid depressurization quench), infrared laser irradiation of the burning surface to increase burning rates, development of inherently unstable combustion chamber geometries (producing either local pressure or velocity perturbations), and electrically sensitive hydroxylammonium nitrate (HAN)-based formulations in which burning rate is controlled by a voltage potential. However, these techniques are limited in that they either can only be used with low flame temperature (low specific impulse) propellants, result in low propulsion system mass fraction (pintle), are only capable of producing a single perturbation, or are formulation specific.

To gain control over a combustion process, combustion plasma enhancement has been demonstrated in electrothermal-chemical (ETC) launchers, in which solid gun propellant ignition flame spread, pressurization rate, and global propellant burning rate improvements were observed. With ETC enhancement, burning rate improvement of up to 35% is possible and further enhancement is speculated to be possible with higher solid loading. However, ETC launchers (e.g. capillary plasma generation) are capable only of single plasma injections or have limited volume.