Ejector mode performance improvement of rocket-based combined cycle engine designed for dual-ramjet mode

Rocket-based combined cycle engine integrating multi-mode operation accomplishes an excellent performance under various flight speed conditions. Generally researchers selected dual-ramjet mode as the cruise and design point with adjusting heat addition method to improve the performance under other modes. To analyze the difficulties during the multi-mode design, a unilateral expansive flowpath through central rocket ejection was investigated to analyze the effects of the mixing ratio of oxygen and fuel and the mass flow rate of the primary rocket plume. The results indicate that the mixing ratio increase can significantly strengthen the entrainment amount. There is an optimal operating rate to obtain the highest entrainment ratio due to Fabri choking limit induced by a confined path width. However, the excessively divergent afterbody based on dual-ramjet results in the under-expansion issue of the exhaust gas and negative thrust of the nozzle. The multistage ejection method can effectively overcome this shortage by compressing the exhaust gas. But with the flight speed increasing, the existence of upstream bow shock induces high inlet resistance. Adding extra duct can effectively solve the problem by decreasing inlet convergent ratio and sucking more secondary flow for combustion.