Effect of a Rearward-Facing Step on Plasma Ignition in Supersonic Flow

The effect of a rearward-facing step on plasma ignition in supersonic How was experimentally and numerically investigated. In the experiment, the rearward-facing step was installed between a plasma jet torch and a fuel injector. The step height was set at 4 mm and was located 14 mm downstream of the plasma jet torch and 10 mm upstream of the fuel injector. The fuel jet was injected perpendicularly at sonic speed behind the step into the main flow of M = 1.7. In the experimental results, with installation of the step, the pseudo shock wave did not travel upstream beyond the step, and there was therefore a threshold electric power input above which a large wall-pressure increase due to combustion appeared. However, the advantage of an installation of the rearward-facing step to the straight duct was not apparently observed in the ignition tests. Numerical simulation showed that the reasons for this result were a delay of mixing of the plasma jet and the fuel jet and low temperature in the recirculation zone behind the step. Though a drastic improvement of mixing or the fuel jet with the main flow in the recirculation zone behind the step was demonstrated, the static temperature there was too low to incur a strong combustion reaction.