Theoretic analysis and experimental investigation on ejector/ramjet mode transition of RBCC

The Investigation progress on ejector/ramjet mode transition of rocket-based combined cycle (RBCC) engine of Northwestern Polytechnical University rocket ejector/ramjet research group was summarized in this paper. The performance evaluating method that considers the RBCC restrictive real operation condition of ejector and ramjet mode was set up based on aircraft design flow chart. The change in specific impulse, thrust coefficient of ejector and ramjet mode with flight trajectory with different fuels were discussed. The selection method that bases on optimum specific impulse and minimum thrust fluctuation of ejector/ramjet mode transition interval are put forward. Considering the reference flight trajectory of a certain mission, the reasonable mode transition interval in condition of 2.6 ± 0.1Ma flight velocity and 11.7-12.9km flight height can be drawn. Based the theoretic analysis results, the integration numerical investigation for the combustion flow field of inlet and combustor was carried on. The transformation rule of flow and combustion mode and inlet operation state during the mode transition transient process was investigated. Based on the experimental investigation of ejector and ramjet operation process and numerical simulation of mode transition, ejector and ramjet mode smooth transition of RBCC was achieved. The results show that:(1) the main cause of thrust fluctuation is the discontinuity of combustion and heat reaction area along the flow direction; (2) the reserved hot gas of primary rocket plays the role of flame holder and combustion enhancement; and the reasonable mass flow rate of the reserved hot gas not only can shorten the mode transition time, but also can improve the specific impulse of RBCC; (3) based on the numerical simulation result the mode smooth transition scheme through modulating the fuel injection scheme and throttling style of primary rocket was brought forward; the mode smooth transition scheme is validated by numerical simulation and obtains positive results; the numerical simulation results provide the combustion control approach of experiment. (4) Mode smooth transition is achieved through appending the torch in the combustor discontinuity area of combustion and heat reaction under the mode transition scheme of primary rocket instantly throttling.