Effect of boundary layer thickness on supersonic combustion in a scramjet combustor

In this study, the effect of boundary layer thickness on supersonic combustion in an ethylene-fueled scramjet combustor under Mach 5.5 flight conditions is studied by employing experiments, numerical simulations, and theoretical modeling. The plate flow quantitative results show that the absolute thickness of the boundary layer is higher for a larger combustor. But the relative thickness is thin. Although boundary layer thickness changes greatly as the combustion chamber scale enlarges, the influence on the transverse jet and cavity flow is limited. In contrast, the combustion chamber scale change has a great impact on the combustion. More violent flames exist in large-scale combustion chambers. A theoretical model demonstrated that a large subsonic region led to a long fuel residence time, resulting in larger Damköhler numbers. This indicated that a large combustor could maintain large combustion. Based on the above analysis, although the relative thickness of the boundary layer is thinner, the absolute subsonic region of the boundary layer full of combustion is increased, which is conducive to intense combustion. In addition, a verification calculation of the 50 mm shortening isolation section is carried out. It is found from the flame cloud diagram and the quantitative wall pressure data that the combustion is significantly weakened.