Plasma and Photoionization Approaches for Combustion Initiation

"Ignition and flame holding is one of the key problems in development of ram/scramjet engines in the range of flight Mach numbers from about 4 (the minimum Mach number for ramjet operation) to 7. At Mach number less than 7, the static temperature at theentrance to the combustor is below 1,200 K, and the unassisted ignition delay time is in the millisecond range. At flow velocities of 1,000-2,000 m/s, the unassisted ignition would occur at distances greater than several meters downstream. Thus, reductionof the ignition delay time down to 1-10 microseconds is indeed critical.Thus, there is a clearly identified need and opportunity to develop an efficient plasma ignition and combustion assistance system. We propose to design, test, and develop an efficient plasma ignition and combustion-assistance device, primarily targetedtowards hydrocarbon-fuel ram/scramjets. The approach that we propose is to accomplish ignition with very high E/N nanosecond-scale pulses repeated at a rate of up to 100 kHz. Very strong electric fields would generate high-energy electrons that are veryeffective in ionization, molecular dissociation, and electronic excitation at low gas temperature, while minimizing stagnation pressure losses due to reduced heating. Phase I of this research program will increase the present understanding of combustion ignition through the creation of a kinetic model. This initial work will model will model a methane/air mixture. Results of this work will establish the foundationfor modeling of more realistic hydrocarbon fuels such as ethylene and JP-10 in Phase II.The experimental work in Phase I will establish quantitative data which will be used to validate the kinetic model. This work will also result in a quantitative comparison of the relative effectiveness of both conventional (DC spark and laser) ignitionprocesses and that of repetitively pulsed high-voltage (high E/N) plasmas ignition. These results coupled with results from additional microwave flame enhancement tests will provide information critical to the development of