Research On The Performance Of Rocket-based Combined-cycle (rbcc) Ejector Mode

Rocket ejector mode is one of Rocket-Based Combined-Cycle engine's operating modes, it is used in the RBCC engine's takeoff and accelerating phase. Based on the dual combustion ramjet of the Johns Hopkins University Applied Physics Laboratory, a new structure was created which was an annular-jet added to the dual combustion ramjet. Number simulation and experimental research are used in this paper to investigate the performance of the rocket ejector mode.In numerical computation aspect, an one-dimension model of number analysis was built to research the influence of rocket ejector mode's performance by changing oil injection in rocket's combustor and in second combustion. The model contained a pure rocket model, an mixture model and a second combustion model. In the research a method was adopted which analyzed and compared outlet's parameter and system's thrust force of the pure rocket, the ejector and the second combustion.This mode used ethanol and gaseous oxygen as fuel. The numerical computation's result shown that:(1)In pure rocket thrust of system wasn't affected by changing of ethanol's concentration; when the excess oxygen coefficient of rocket's combustor was between 0.5 and 1.0 the system can produce more thrust force than it was big than 1.0; the gas's static temperature of ejector rocket's nozzle is highest when the excess oxygen coefficient was equal to 1.0; the gas's velocity of ejector rocket's nozzle was 2~3 Mach. (2)When the ejector rocket's burned gas mixed with ejected air, the velocity of mixing gas declined to about 0.45 Mach, the static pressure of mixing gas ascended, but still less than the pressure of atmosphere; thrust of the system declined. (3)After second combustion, the velocity of gas improved dramatically, and the static of gas dropped; due to the restrictor of second combustor's constant cross-section shape, the velocity of gas can't breakthrough sonic speed; heat choking was brought when the velocity of gas equal to velocity of sound, in the same time the velocity, the static pressure and the temperature of gas all held the line. In this computation model, compared to the pure rocket's parameter, the thrust and the specific impulse of system contained second combustion can enhance 108% and 89.1%. In a word, rocket ejector mode's second combustion can remarkably increase the system's thrust.In the experimental investigation aspect, this paper investigated the transformation of the rocket ejector mode's performance in diverse excess oxygen coefficient of the rocket's combustor, various flow mass and different structures. The experiment was based on direct-connect experimental system which can measure thrust at sea level static state. There was fuel-enriched in the combustion of rocket. Numerical analysis model and calculate program of this paper were verified based on experimental data, percentage error was less than 12%.From the experimental investigation, some results were found which are displayed as follow: (1) When the combustion of rocket was fuel-enriched, the increment of ethanol's flow mass didn't affect the thrust, and that reduce the system's specific impulse. But the increment of oxygen's flow mass observably enhanced the thrust, and the same to the specific impulse. (2)In this paper, increment of the excess oxygen coefficient in rocket's combustor augmented system's specific impulse. (3) When ejector canister added to ejector rocket, the system's thrust descended obviously, average descending pitch was 20%. (4) The increment of ethanol's concentration observably enhanced the specific impulse. (5)The press of combustor was affected by the total mass flow and the excess oxygen coefficient. The increment of the total mass flow or the excess oxygen coefficient could enhance the press of combustor; the higher press of combustor may produce a higher specific impulse. (6)If the excess oxygen coefficient was too low, global bulge would be produced on the ejective flame. The flame's color and shape had a firm relationship with the ethanol's concentration and the excess oxygen coefficient of combustor.