On the Analysis of Scale Effects of Flame Stabilization in Scramjet Combustors

Scale effects of flame stabilization in scramjet combustors at Mach 2.52 are investigated through experiments and numerical simulations based on two geometrically similar combustors. As the equivalence ratio increases, the combustion mode will change from Scram to Dual to Ram. However, the larger combustor has a delayed mode transition. The scale effects of flame stabilization are also reflected in the changes of heat release, precombustion shock train length, jet penetration depth, and reaction zone location. The combustion flowfields of different-scale combustors exhibit numerous differences under different combustion modes. However, after shortening the isolator of the proportionally scaled small-scale combustor, the combustion flowfield is closer to that of the large-scale combustor. Further analysis reveals the reason for the inconsistent scale effects of flame stabilization under different combustion modes. The probable reason is that the boundary layer, which does not change proportionally with the combustor scale, has different effects on the combustion under the three modes. Compared with the Scram and Ram modes, the scale effect in the Dual mode is the most significant because the strong interaction between heat release and the boundary layer amplifies the slight difference in the relative thickness of the boundary layer.