Development of Plasma Torches with High Performance for Scramjet Combustors.

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For the ignition and flame stabilization in combustors of scramjet engines, a method where an arc discharge is formed along the wall (direct arc discharge method) was proposed. In the direct arc discharge method, chemically active radicals produced by arc discharges can be used more effectively compared to the case of conventional plasma torches. Following results were obtained :1. The direct arc discharge method showed an excellent ability for the ignition and flame stabilization in supersonic flows, when the cathode is placed at upstream and the anode, at downstream flatly to the wall surface, and a carrier gas is injected through the gap of them.2. For the case with a wall step, a geometry, where the upstream surface is taken as cathode, and the downstream surface, as anode, and a carrier gas is injected through the gap at the bottom of the step, showed a successful result.3. Fuel-air mixtures showed an excellecn ability as carier gases.An experimental study was made to establish low power plasma jets (order of 100 W) with high exhaust gas temperature and high thermal efficiency. From detailed examination on the distance between cathode and anode, and the anode geometry, following results were obtained :1. Low power nitrogen plasma jets with a stable operation under atmospheric pressure were established with the combination of a high voltage power source and a high stabilizing resistor.2. An improvement in thermal efficiency and jet temperature was made by constructing the upstream part of the anode nozzle with boron-nitride and increasing the distance between the cathode and the anode.3. As for the anode geometry, the performance of the plasma jets becomes high with the decrease of throat length, but the optimum value of throat diameter changes for the maxinum thermal efficiency and the maximum plasma jet temperature.