Experimental Study on Scale Effects of Kerosene Combustion in Scramjet Combustors

The combustion characteristics in two geometrically similar kerosene-fueled scramjet combustors with mass flow rates of 0.69 and 1.41 kg/s are experimentally investigated to explore the scale effects of flame stabilization at Mach 2.52 condition. As the equivalence ratio increases, the combustion usually changes from weak to intensive to blow-out mode. The weak combustion has little effect on the flow field, whereas the intensive combustion has the opposite effect. The transition combustion tends to occur between different modes. When the single injector is used, compared with the small-scale combustor, intensive combustion cannot occur in the large-scale combustor, and the flame stability range is also narrower. One probable reason is that as the combustor scale increases, the boundary layer becomes relatively thinner, resulting in a smaller low-velocity zone and a faster mainstream velocity at the downstream wall of the cavity, which is not conducive to the flame propagation upstream to form the intensive combustion. After shortening the isolator, all cases with intensive combustion in the small-scale combustor are transformed into weak combustion, further confirming the speculation. Compared to the single injector, the dual injector is required in the large-scale combustor to achieve intensive combustion and a wider flame stability range.