Experimental Investigation on the Plasma Torch Used for Scramjet Ignition Enhancement

A high frequency arc discharge plasma torch was specially designed for ignition enhancement in scramjet combustor. At first, the process of plasma injection into quiescent air was investigated experimentally through CCD camera and schlieren technology. Then, the energy property characterization of active particle distribution was measured by emission spectrometry. Several kinds of working gas under different injection pressures were compared. Finally, the typical supersonic flow-field structure with plasma cross-injection was obtained. The results show that plasma jet energy is concentrated near the jet axis, which has the maximum attenuation in the downstream as far as 2 cm from the outlet. The working gas and injection pressure have great effect on emission spectrometry and the process of jet expansion. The case with N2 under higher injection pressure shows better performance of energy exchanging process when comparing with air and argon. From the emission spectroscopy, we can see that plasma from nitrogen consists of nitrogen and oxygen atom mainly, whose intensity decreases with increasing distance from the nozzle, while it increases with the increase of pressure. When plasma was vertically injected into supersonic flow-field, bow shock wave and mixing layer structure were formed with thicken mixing layer, which helps enhance the mixing process between active particle and incoming air.