A hydrocarbon-fuel injection and ignition/e ame-holding system consisting of an aerodynamic-ramp injector and a DC plasma torch was designed for a scramjet vehicle operating from Mach 4 to Mach 8. It was tested in an unheated Mach 2.4 e ow for initial evaluation. The injector consisted of two rows of two holes, angled downstream, and toed in to create additional vorticity and enhance mixing. The plasma torch was placed downstream of the injector at three different locations. The experiments involved ethylene injection through the aeroramp at jet-to-freestream momentum-e ux ratios from 1.4 to 3.2. Methane and nitrogen were used as the main feedstocks for the plasma torch. The power output of the plasma torch varied from 1500 to 3000 W. Results showed that nitrogen outperformed methane, and increasing the oxygen content at the plasma/fuel-plume interface signie cantly improved the potential for ignition and e ame propagation. The methane and nitrogen feedstocks performed best at the closest and middle downstream torch stations relative to the ethylene-fuel plume, respectively. Because of the low static freestream temperature (131 K), very little heat release was produced under these cold-e ow conditions. Tests in a model scramjet combustor with hot e ow are needed to complete the evaluation of this system. In addition, at all three torch stations, the counter-rotating vortex motion of the fuel-injector plume lifted up the plasma-torch plume. As a result, the downstream temperature-plume cores were 2.5 and 3.5 times higher at injector jet-to-freestream momentum-e ux ratios of 1.5 and 3.0, respectively, compared to the torch alone.
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Jacobsen et al. (2003) studied this question.