Engine system analysis upon a Rocket-Based Combined Cycle (RBCC) engine for the booster stage of a TSTO launch vehicle was conducted, to evaluate the benefits of hypersonic air-breathing technology upon the performance of the launch vehicle. Hydrocarbon fuel (namely ethanol) and LOx was selected as the propellant of the vehicle to enable easy handling and good packaging of high-density fuel into the airplane-like vehicle shape. First, parametric study on the ramjet-duct portion of the RBCC engine was conducted for fixed embedded rocket engine parameters. Then the rocket engine parameters were varied for the fixed ramjet-duct parameters to attain best performance with a fixed ramjet-duct projected area. The analysis method and primary results are herein reported.

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Downstream combustion ramjet-mode operation in a dual-mode engine combustor was studied experimentally with a Mach 2.5 wind tunnel. In this downstream combustion ramjet mode, subsonic combustion was attained in the downstream straight-duct section without a geometrical throat. The experimental results are presented. The total temperature and the total pressure in the vitiation air heater were 800 K and 1.0 MPa, respectively. Pitot pressure and gas sampling were measured on the exit plane of the combustion model. The combustion conditions of the downstream combustion ramjet mode were compared with those of the usual upstream combustion ramjet mode. Better thrust performance and combustion were observed in the upstream combustion ramjet mode. However, in the case of the downstream combustion ramjet mode, injection of a larger amount of fuel was possible and a large impulse function was attained. The downstream straight duct was required for sufficient reaction. The fuel did not go far upstream in the separation region in pseudo-shock. Nomenclature ER = equivalence ratio M = Mach number P i = wall pressure at the entrance of the combustor P p = pitot pressure P w = wall pressure x = distance from backward-facing step y = vertical distance from the bottom z = transverse distance from side wall surface η c = combustion efficiency φ = equivalence ratio

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Engine system analysis upon a Rocket-Based Combined Cycle (RBCC) engine for the booster stage of a TSTO launch vehicle was conducted, to evaluate the effects of hydrocarbon fuel type upon the performance of the engine and the whole launch vehicle. A higher thrust and cooling performance with methane was shown, while some technical challenges were also noted. Combination of the scramjet flow pass and the rocket engines, i.e., rocket engine being embedded into the scramjet flow pass or separately mounted to the airframe, was varied to show that the separated configuration mitigated cooling problem, and resulted in a better performance for mid-speed regime.