Ignition of Supersonic Propane Air Flows Initiated by the Direct Current Discharge: Experiment and Numerical Modelling

Two types of inflammation, realized by cross - longitudinal arc discharge were investigated. Mutual influence of flow and flame led to formation of straight shock or shocks combination in front of heat supplier in one of two mentioned regimes. In its turn formation of shocks led to flow slowdown, pressure and temperature increase. Conditions for mixture ignition varied and we got unstable pulsed inflammation. It was experimentally achieved and analyzed. Inflammation was followed by sharp peak of pressure that was shock. It shifts stoichiometry point and stops plasma inflammation. As consequence we had a combination of inflammation and combustion pulses, followed by shocks. Ignition process existence was verified by spectral OH luminescence and integral luminescence obtained from the photo-amplifier. Exact correlation with pressure detectors was observed. In other area of electric parameters we could observe stable non-self-maintained inflammation of the propane -air mixture, which continued during the whole time of the discharge existence. It was confirmed by photo-amplifier data. Obtained results show that existence time of the discovered inflammation mode is (0.6 - 1 s). It is 6 times greater than duration of stationary flow establishment. That-s why described regime can be characterized as stationary non-self-maintained combustion of the high-speed propane-air mixture. High speed video measurements have shown space character of inflammation and further combustion wave. Streamer propagation is realized in complicated tracks that reflect turbulent structure of flow. In such a way integral area of energy input is three dimensional one and occupies 50% of channel section. Structure of streamers repeats form of reverse stream in area of step disposition. Numerical modeling verified appearance of quasi bounds in front of plasma and described parameters of flow close to that, found experimentally. Nevertheless model should include non thermal plasma mechanisms of inflammation and gas dynamic conditions of discharge.