Combustion Enhancement and Drag Reduction by Increasing Blockage in Solid Rocket Scramjets

This study conducted numerical simulations to enhance particle combustion and reduce drag by increasing blockage in a solid rocket scramjet combustor. The simulation was performed using the Eulerian–Lagrangian model, under flight conditions of Mach 6 at 25 km, with an equivalence ratio of 0.56. Ramps of different heights were installed near the exit of the combustor to act as a throat and alter the blockage ratio. The results indicate that higher ramps increase blockage, resulting in higher temperature and pressure. With higher blockage, the reaction rates of kinetics-controlled particles significantly accelerate due to the increased temperature and pressure. In contrast, the reaction rates of diffusion-controlled particles remain relatively unchanged. Nevertheless, the combustion efficiency of both particles is enhanced owing to the longer residence time. Higher blockage increases the wave drag due to the intensified shock train. However, the calculation of Rayleigh loss indicates that increasing blockage reduces the heat drag by a maximum of 77.42%, even with more heat release. Despite the additional drag caused by the introduction of ramps, the overall total pressure loss is decreased by up to 10.67% (with 35 mm ramps). These findings provide novel insights for the design of solid rocket scramjet engines with high performance.