Investigation Of Rocket-Based Combined Cycle Engine Ejector Mode

Rocket based combined cycle is a combination of the advantages of the rocket engine and intake engine, which features high thrust to weight ratio and high specific impulse and realizes the optimality of performances in the whole ballistic trajectory. As a reusable power system of spacecrafts, RBCC has a promising prospect in the future. ejector mode, which is a key technique of RBCC, is significant to overall design and performance enhancement. Theoretical analysis, numerical simulation and experimental research were applied to investigate the performance and the influential factors of the ejector mode.For theoretical analysis part, one dimension model and related code was developed. Thermodynamic calculation was used to precisely calculate the main rocket and secondary combustion. Results suggested that complete mixing solution could not always be achieved for constant area structure, total thrust was enhanced and the pressure of secondary combustion chamber was reduced as the ejector coefficient enhanced, and maximum thrust was achieved under the third critical ejector coefficient. When enhancing the primary flow mach number, thrust may deduce under the same ejector coefficient. When the primary flow mach number is relatively big, the maximum thrust and thrust-plus can be achieved. Within the range of constant area structure solution, the performance of the constant area structure is better than the constant pressure structure, and the difference grows bigger as the incoming flow mach number increaces.For numerical simulation part, numerical simulation was carried out to investigate different structures and different conditions, without considering the secondary combustion. Important conclusions were drew as follows: ejector mode should work under supersonic condition, which corresponds to the extreme ejector coefficient under the same condition. Mixer length is of great influence on the evenness of the outflow. If the mixer is too short, the primary and secondary flow will not be able to mix completely. Radial mach number and the total pressure of the outflow varies a lot, an optimized length of the mixer exists. The structure of the mixer is of great influence on the ejector performance. Under the same condition and inlet cross section area of the mixer, the diffusive structure has the highest ejector coefficient and the lowest anti-backpressure ability. The contraction structure has the lowest ejector coefficient and the highest anti-backpressure ability. The constant area structure is medium in performance.Experimental results show that the length of the mixer is influential in anti-backpressure performance but the influence is not significant. Double main rockets structure can effectively enhance the anti-backpressure ability. As the enhancement of the total pressure of the secondary flow, the ejector coefficient gradually increased, and the anti-backpressure ability gradually decreased.