Testing of a scramjet engine with a strut in M8 flight conditions

To attain intensive combustion in M8 flight conditions at which a basic strutless engine failed to initiate intensive combustion, a strut for the inlet contraction ratio of 5 with fuel injectors was installed and the engine was tested in M8 flight conditions, with a total temperature of 2550 K, a total pressure of 10 MPa and an airflow Mach number of 6.7. In the small fuel flow rate regime, pressure increments in the diverging combustor were observed due to the boundary layer combustion. This pressure rise was enhanced with the auxaliry injection from the strut which enhanced the mixing of the main fuel. The intensive combustion within the constant area combustor was attained at higher fuel flow rates, which resulted in transitions to an engine unstart condition. A prediction method was adopted to estimate the limiting fuel flow rate for attainment of the intensive combustion within the constant area combustor and for the transition to the unstart. Introduction Supersonic combustion ramjet (scramjet) is expected to be the most effective propulsion system for Single Stage To Orbit (SSTO) transportation system and the hypersonic transportation system of next generation. Many studies on components of the scramjet engines such as inlet, combustor and nozzle have been carried out. On the other hand, intensive interactions between these components are expected in real engines [1]. Thus, it is necessary to conduct testing of complete engine model to investigate the interactions and the engine performances. However, only limited data on these complete engine models and their performances have been published [2]. Using a blow-down type wind tunnel facility (denoted as RamJet engine Test Facility; RJTF) at NALKRC, we have conducted tests of a scramjet engine at various flight conditions from M4 to M8 [3-8]. This engine had a sidewall compression type inlet section with a contraction ratio of 2.9. The ratio was limited to assure starting capability in the M4 flight conditions. However, this low contraction ratio resulted in low pressure levels at the combustor entrance in the M6 and M8 flight conditions, and no intensive combustion within the engine was observed at both flight conditions [3, 6]. To attain intensive combustion in M6 flight conditions, it was necessary to place a strut within the engine for further compression and low velocity region enlargement [4]. To attain intensive combustion also in M8 flight conditions, a strut for the inlet contraction ratio of 5 with fuel injectors was fabricated and installed. Present paper reports the results of the engine tests in the M8 flight conditions, with a total temperature of 2550 K, a total pressure of 10 MPa and an airflow Mach number of 6.7. Copyright © 1998 by American Institute of Aeronautics and Astronautics, Inc. All right reserved. * Researcher, Ramjet Combustion Section, Ramjet Propulsion Dvision. Member AIAA. t Head, Ramjet System Section. Member AIAA. $ Senior Researcher, Ramjet Aerodynamics Section. § Head, Ramjet Combustion Section. Member AIAA. 1 Head, Ramjet Guidance Section. Member AIAA # Head, Research Coordinate Office. Experimental apparatus Wind tunnel facility and test conditions The RJTF was designed to simulate flight conditions of M4, M6, and M8. The facility is equipped with two heating systems to obtain high enthalpy flow. A storage air heater (denoted as SAH) is used to obtain pure hot air for the M4, M6, and M8 flight condition tests. Two types of vitiation air heaters (VAH) fueled by H2 are used to obtain vitiated hot air for the M6 and M8 flight condition tests, respectively. The M6 flight conditions are achieved with the SAH alone or the VAH alone (denoted as M6S and M6V conditions, respectively), whereas the M8 conditions are achieved with a combination of the SAH and the VAH. Table 1 shows the operational conditions of the RJTF at the simulated Mach 8 flight conditions. The high enthalpy flow obtained at the heaters was accelerated through a rectangular nozzle. The exit cross section of the nozzle was 510 mm x 510 mm. The engine model was set in a low pressure chamber which was connected to a steam ejector system to reduce the pressure within the chamber for simulation of high altitude atmosphere. The engine model was located in such a way that it breathed in the boundary layer on the facility nozzle wall. The displacement thickness of the boundary layer was about 33 mm. Table 1 Flow condition in M8 conditions Stagnant Engine inlet