Scramjet Mode Tests of a Combined Cycle Engine Combustor

Abstract

A combustor model of the combined-cycle engine was tested. The model had two rockets, which supplied fuel-rich, pre-combustion gas as fuel for air. Gas hydrogen and gas oxygen were used as propellants. The test facility consisted of an air supply section, a rocket section, a straight duct section and a divergent duct section. Total temperature of the vitiated air was 2000 and 2400 K, and the total pressure of the air was 1 MPa. The air flowed into the air-breathing part at Mach 2.4. In the tests, the wall pressure increased downstream of the rockets. The combustion efficiency was around 0.8 according to gas sampling and pitot pressure measurement. In a model configuration with a long straight duct, combustion gas was decelerated to subsonic speed and choked thermally at the exit of the straight duct. In another configuration with a short straight duct, combustion progressed in the downstream divergent duct. When non-reacted mixture was injected from the rockets, wall pressure increased quickly, comparing to the pressure with injection of the combustion gas from the rockets. NOMENCLATURE A = cross section Fc = impulse function of combustion gas M = Mach number (O/F)r = mass ratio of oxygen to fuel in rocket P = pressure Pta = total pressure of inflow air Ptc = total pressure of combustion gas Pw = wall pressure Pwi = wall pressure at entrance of combustor P0 = 1 atm pressure T = temperature Tta = total temperature of inflow air x = distance from the position of the rocket nozzle exit along the airflow direction y = transverse distance from side wall surface z = spanwise direction from the rocket side wall surface φ = equivalence ratio for airflow γ = ratio of specific heats ηc = combustion efficiency τr = reaction time INTRODUCTION Combined cycle engines for the Single-Space-toOrbit space plane has been studied. One of the engines is composed of an ejector-jet mode, a ramjet mode, a scramjet mode and a rocket mode. The engine has rocket engines and can operate from take-off to orbit. Figure 1 shows a schematic diagram of the operating conditions of the engine. In the engine, an ejector rocket works as a rocket engine in the ejector-jet mode and the rocket mode, as a torch in the ramjet mode, and as a fuel injector of the fuel-rich, precombustion gas in the scramjet mode. The authors proposed an engine as shown in Fig. 2 based on the conceptual study. The engine has no second throat at the exit of the engine. With such configuration, subsonic combustion was attained in *Leader, Engine System Team, Combined Propulsion Research Unit. Senior member AIAA. † Senior researcher, Engine System Team, Combined Propulsion Research Unit. ‡ Senior researcher, Engine System Team, Combined Propulsion Research Unit. Member AIAA. Fig.1 Schematic diagram of the combined cycle engine operating conditions. Fig. 2 3-D image of combined cycle engine. 12th AIAA International Space Planes and Hypersonic Systems and Technologies 15 19 December 2003, Norfolk, Virginia AIAA 2003-7051 Copyright © 2003 by Japan Aerospace Exploration Agency. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. American Institute of Aeronautics and Astronautics 2 the combustor tests. The ramp channel between the rockets allowed the breathed air to flow toward the airframe side. In the scramjet mode, fuel of the hydrogen/ oxygen pre-combustion rocket exhaust flows parallel to the breathed supersonic airflow. Under the parallel fuel injection, sufficient mixing and reaction are key subjects in the scramjet. Though the configuration of the fuel injector is different from that of the scramjet engine, mixing and reaction are also key subjects in the scramjet mode of the combined-cycle engine. Therefore, operation of the engine under the scramjet mode should be demonstrated, and characteristics and problems under the mode have to be made clear to develop the combined-cycle engine. In the studies of the strutjet, combustion tests in the scramjet mode have been conducted. 9,10 In this study, a combustor model was made based on the authors’ proposed combined–cycle engine configuration, and was tested experimentally at the scramjet mode under the Mach 2.4 vitiated airflow condition. Results of the tests, herein, are presented. TEST FACILITY AND COMBUSTOR MODEL Figure 3 shows the experimental setup. The test facility for supply of the vitiated supersonic airflow Fig. 3 Schematic diagram of the combined cycle engine combustor model and test facility.