Investigation On Performance And Influence Factors Of Rocket Ejector Mode Of RBCC

Rocket-based combined cycle (RBCC) will be promising propulsion system to achieve hypersonic flight, and has extensively application foreground in both military and civil usage. Rocket ejector is the alternative power of RBCC during low-speed operation. The utilization of rocket ejector will be important for structural integration, and will decrease weight and complexity of the motor. Theoretical and experimental approaches are used in this paper to investigate the performance of rocket ejector with strut characteristic and its influence factors.In the theoretical aspect, performance analytical model of was proposed, in which allowances were made to allow for variable cross-sectional area, include the heat release of chemical reaction, and allow for mass addition. Software was generated, and performance of rocket ejector was analyzed accounting for heat release location, flow parameters and structural configuration. It is shown that when the exit area of secondary nozzle and the fuel/oxidizer ratio is fixed, the increase of mass flow rate of secondary flow lead to the decrease of velocity of mixed flow, and increase of total mass flow rate. The synthetical result of these two phenomenon cause the increase of thrust of rocket ejector, but the increasing magnitude is relatively small, indicating that these is no necessary to claim large bypass ratio in rocket ejector design. In the comparison between two configurations, the typical one has better performance, indicating the importance of pressure ratio. The thermodynamic cycle analysis shows that the increase of pressure in secondary combustor will enhance the performance of rocket ejector.Unstructured mesh was used in 3-D numerical simulation to simulate the influence of secondary nozzle on performance of rocket ejector, ejecting ability and mixing condition. The results indicate that with decrease of exit area of secondary nozzle, the bypass ratio is decreasing, and the static pressure in integrated ejector combustor is increasing, and mixing condition becomes better. There exists an optimal exit area of secondary nozzle to get maximum thrust of rocket ejector.In the experimental aspect, Rocket ejector experimental system was designed and fabricated. The system includes test motor with strut characteristic, free-jet gas supplysystem, liquid fuel injection system and data acquisition system. Using solid rocket gas generator, sea level static ejector mode experiment was conducted. The influence of primary flow and secondary nozzle geometry on ejector effect and thrust was investigated, and the approach to increase thrust of rocket ejector was found gradually. The experimental results indicates that the secondary mass flow increases with increasing of primary mass flow rate, but the bypass decrease because the primary mass flow rate increase more rapidly than secondary mass flow. The expansion configuration shows low thrust property due to low pressure in flow path. The secondary nozzle changes the pressure distribution in ejector combustor, and decreases bypass ratio, but obtain more completely mixing. The conclusion that the optimal secondary nozzle exit area generating the maximum thrust agrees well with the numerical simulation, indicating that the exit area of secondary nozzle should be optimized according to structure and flow parameters during design.Using swirl atomizer designed by this paper, kerosene was injected into the ejector combustor, and achieved steady combustion. This made a solid foundation for the future study on combustion organization.