An Investigation of Controlled Oscillations in a Plasma Torch for Combustion Enhancement
Sanders, Darius Demetri
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The oscillating plasma torch is proposed as a potential device that will produce an oscillating shock and resulting control of the supersonic combustion process. This research will capitalize on previous results [Gallimore, 1998] which indicate that the plasma torch oscillations originate from the inherent oscillations of the voltage applied to the torch. The aim of this research is to thoroughly investigate the oscillation behavior of the plasma torch with the plan of ultimately controlling the oscillation at chosen frequencies. A modulating power system used for dynamic control of the plasma torch oscillation was designed and tested in quiescent conditions (no flow), Mach 2.4 cold supersonic flow, and Mach 2 heated supersonic flow conditions. The oscillating plasma torch used nitrogen feedstock and was operated over a frequency range of 2Hz- 4kHz. A dynamic torch model using the hybrid Mayr-Cassie electric arc model was developed to predict the plasma torch electric arc response at appropriate frequencies for interaction with supersonic combustion. In quiescent conditions, the dynamic response of the plasma torch power system and plasma jet were characterized using signal processing techniques and high speed video imaging. High speed Schlieren images were used to determine the behavior of the oscillating plasma jet in Mach 2.4 cross flow and its influence on the induced shock structure. The unsteady nitrogen-fed torch was integrated with the flush walled 4-hole aerodynamic ramp injector using hydrogen and hydrocarbon fuels at the University of Virginia Aerospace Research Lab (ARL) heated Mach 2 supersonic flow. Unsteady pressure variations from the oscillating shock produced by the plasma torch were recorded using recess-mounted Kulite pressure transducers. Also, measurements of the static pressure of the combustion produced by the oscillating plasma torch were obtained. The oscillating torch system performed well over a range of different flow conditions. It will enable active control input to the combustion process. The controllable unsteady blockage might provide a type shock interaction needed to increase turbulence and mixing augmentation [Kumar, et al. 1987].
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