Plasma torch igniters for a scramjet combustor

Development of a versatile plasma torch, which carries desirable features for being an ignition aide within a supersonic-combustor, is studied. The desirable features include 1) easy to be installed, aligned, and maintained, 2) a divergent nozzle for supersonic plasma jet, 3) an additional port for fuel injection, and 4) a microwave adaptor arrangement to couple additional power (from microwave as well as arc discharge) to the torch plasma. The plasma jet generated by this torch is described by the cycle energy of the discharge and through imaging of its plume under various conditions, combination of without and with additional microwave power and the supply gas pressure to the torch. This torch system, with its high voltage discharge, is operated in periodic (60-Hz) mode. The capacitors in the circuit of the power supply are charged at the line frequency of 60 Hz, resulting in a cyclical discharge. The cycle energy is up to 28 J. The microwave electric field has a profound effect on the arc discharge. The arc discharge is found to triple its peak power and to have significantly increased size in the presence of microwave, even though the applied microwave energy is relatively low, which is estimated to be about 8 J per cycle. The added microwave electric field outside the nozzle of the torch module also works to increase the penetration depth of torch plume into the supersonic crossflow in the combustor. This is because the microwave electric field can penetrate deeply into the combustor without being affected by the supersonic cross flow.