Flame stabilization in a supersonic combustor with hydrogen injection upstream of cavity flame holders: experiments and simulations

Experimental observations and numerical simulation were conducted to study the flame characteristics and flame stabilization mechanism in a supersonic combustor with hydrogen injection upstream of cavity flame holders. OH radical distribution of the reacting flowfield was obtained using OH spontaneous emission and OH-PLIF (planar laser-induced fluorescence). The supersonic combustion flowfield with L/D = 7 cavity was calculated by large eddy simulation. The turbulence-combustion interaction model was based on a partially premixed flamelet model with a level-set approach. The results showed that hydrogen fuels were transported into the cavity shear; lean mixture and rich mixture were produced in the internal cavity and the declining jet, respectively. An approximately steady partially premixed flame front exists in the cavity shear layer. The flame front propagates and extends to the region around the fuel jet due to the interaction of counter-rotating vortices induced by the jet with the cavity shear layer. The flame front sustained in the shear layer likely penetrates the jet core and ignites the whole jet. Behind the flame front, most of the jet beam is burned as diffusion flames. The physical process of the flame stabilization demonstrated the similarity with triple flame characteristics, which indicted that triple flame theory might be the basic flame stabilization mechanism of the cavity flame holders.