Flame Characteristics in Supersonic Combustor with Hydrogen Injection Upstream of Cavity Flameholder

Flame characteristics and a plausible flameholding mechanism in a supersonic combustor, with hydrogen injection upstream of a cavity flameholder, were investigated in the present study. Instantaneous OH radical distribution of the combustion flowfield was obtained using OH planar laser-induced fluorescence. According to the similarity of experimental observations with different cavities, a typical L/D = 7 cavity was chosen, and its supersonic combustion flowfield with hydrogen injection was calculated by large-eddy simulation. The results showed that the cavity shear layer plays a very important role in the flameholding process. An approximately steady flame existed in the cavity shear layer and hot combustion products were transported into the injection jet by the vortex interaction ofthejet-with-cavity shear layer. Flame then spread gradually following the counter-rotating vortex induced by the jet until the whole injection jet was ignited. Combustion products, which generated from the cavity shear layer and the jet, were convected into the cavity by the unsteady motion of the cavity shear layer and transported with the recirculation flow to the cavity front wall. These hot products and their intermittent combustion then heated up the cavity, and the fuel that entered into the cavity shear layer was preheated. Thus, the flameholding cycle was formed.