Combustion mode and heat release characteristics of a kerosene-fueled rocket-aided ramjet combustor in ramjet-to-scramjet mode transition

In this study, a rocket-aided ramjet engine (RARE) configuration is proposed that is aimed at improving the thrust gap and enhancing the engine thrust stability in the ramjet-to-scramjet mode transition of dual-mode scramjet (DMSJ) engines. The combustion mode and relevant heat release characteristics in the kerosene-fueled combustor during the mode transition are analyzed in detail through numerical simulations and ground direct-connect tests at the simulated flight condition of Mach 6. In the ramjet mode, the combustion mode distribution is dominated by diffusion and supersonic combustion, whereas the heat release comes mainly from diffusion and subsonic combustion. The subsonic combustion mode is that which has the highest heat release efficiency, accounting for 28.6% of the total combustion volume, and contributing 67.9% of the total heat release. The combustion heat release level in the rocket-aided scramjet mode is higher than the simple sum of the pure rocket and scramjet modes. The RARE combustor effectively maintains the heat release level and stabilizes the distribution of several different combustion modes from the ramjet to the scramjet mode using the embedded rocket. Furthermore, a robust method for a smooth ramjet-to-scramjet mode transition is provided for ramjet engines. Compared with the engine operation without embedded rocket, the engine thrust variation is reduced from 50.77% to 1.33% with the aid of the embedded rocket, which enhances the operational stability of the engine considerably during the mode transition.