Transition of Combustion Mode in Scramjet

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Scramjet engines keep high performance in a wide Mach number range by shifling the combustion from the subsonic mode to the supersonic mode. This mode transition is a complicated interaction among mixing, combustion and pseudo-shock wave, and its detailed mechanism has not been clarified. This research project intends to clarify the transition mechanism by separating each phenomenon in the interaction and by controlling each phenomenon independently to investigate its influence to others.As the first step of the research, helium was injected into a supersonic flow produced by a suction-type wind tunnel. The pseudo-shock wave was produced and controlled by a back-pressure valve installed at the exit of the test section. The pseudo-shock wave strongly enhanced mixing of helium. The more upstream the pseudo-shock wave went, the stronger the enhancement effect became, The helium jet injected from the bottom wall of the test section usually spread in the lateral direction by the pseudo-shoc … More k wave, but the helium was diffused in the transverse direction depending on the location of the front of the pseudo-shock wave.In the second step, the back-pressure valve was removed and a plasma torch was attached as an injector. The feedstock of the torch was nitrogen or hydrogen/nitrogen mixture. The pseudo-shock wave was produced by increasing the input power to the torch and/or the fraction of hydrogen in the feedstock. It was found that the pseudo-shock wave was established when the generalized choking condition was satisfied at the exit section.When the front of the pseudo-shock wave went upstream about four times of the duct height from the injection port, the streamwise wall pressure distribution had a peak near the injection prot and decreased in the downstream direction. The shock train in the pseudo-shock wave was seen only upstream of the injection port fuel was injected upstream the plasma torch. These result indicated that the combustion mode shifted from supersonic to subsonic. The amount of heat release measured at the exit section was less than the value required for the thermal choking in the quasi-one-dimensional theory. The transition of the combustion mode resulted increase of the penetration of the injectant, but no significant change was observed in the hydrogen distribution and the combustiorn efficiency. Less