Experimental and Numerical Study on Flame Stabilization in a Supersonic Combustor with Hydrogen Injection Upstream of Cavity Flameholders

Abstract

Experimental observations and numerical simulations were conducted to study the flameholding characteristics and the flame stabilization mechanism in a supersonic combustor with hydrogen injection upstream of a cavity flameholder. OH radical distribution of the combustion flowfiled 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 simulations. The combustion model was based on a two scalar 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 internal cavity and declining injected jet respectively. An approximately steady partially premixed flame front exists in the cavity shear layer. The flame front propagates and extends to region around the fuel jet due to the counter-rotating vortices induced by the jet and the cavity shear layer. The flame front sustained in the shear layer likely penetrates through the jet core and ignites the whole jet. Behind the flame front most of the jet beam is ignited and burned as diffusion flames. The physical process of the flame stabilization demonstrated the similarity with a triple flame theory or edge flame concept, which indicted that triple flame theory might be the basic flameholding mechanism of the cavity flameholders.