Optimization of microwave air plasma apparatus for hydrocarbon combustion enhancement experiments

Demands on flight systems to become smaller, more light weight and faster have led the aerospace community to the development of the supersonic combustion ramjet (scramjet) engine. The scramjet engine is a supersonic air-breathing engine that eliminates the requirement on rocket engines to carry onboard oxidizer. This allows the vehicle to be smaller and more maneuverable or able to carry a larger payload. Supersonic combustion, as in a scramjet engine, poses many challenges. Short combustion chamber residence times result in poor mixing of the fuel and air and incomplete combustion. Challenges in the area of fuels are focused on their ignition delay and burning velocities. Adding highly reactive radical species, such as those found in air plasmas can also be used to increase the decomposition rate of hydrocarbon fuels. The goal of this study is to produce air plasmas in a waveguide/combustion chamber that could be sustained at high flow throughputs for future use as an ignition source for hydrocarbon hypersonic combustion. This setup would ultimately be used to test the effect of air plasma on hydrocarbon combustion. The steps taken in this study to achieve the ultimate goal were: 1.) characterize the power absorption characteristics of plasma in the setup, 2.) produce an air plasma that can be maintained at atmospheric pressures, and 3.) maintain an air plasma at high flow throughputs.