Combustion characteristics of a supersonic combustor model for a JAXA flight experiment

Abstract

JAXA is conducting a flight-ground test comparison program to clarify the “facility effect” on hypersonic aerodynamics and combustion phenomena and to develop a CFD tool for predicting flight data from ground test data. The aim is a flight experiment to obtain data on aerodynamic heating and supersonic combustion under actual flight conditions and to validate the CFD tool using flight data and the corresponding ground test data. This study aimed at determining a flow-path geometry and a fuel injector configuration for a supersonic combustor suitable for clarifying the influence of the different test flow compositions between flight and ground test conditions on combustion. The candidate configurations proposed by the CFD study were evaluated by direct-connect combustion tests using ethylene fuel. The results showed that a combustor flow was symmetric when the fuel equivalence ratio was low and asymmetric when the equivalence ratio and the pressure in the combustor were high. Because an asymmetric flow is unsuitable for validating CFD based on steady RANS, the total equivalence ratio was limited to 0.44. The combustor model uses two-stage fuel injectors and cavity flame holders to combust ethylene fuel. The depth of the cavity flame holder had little influence on combustion. However, the number of injection holes for the injector located downstream of the cavity affected the combustor pressure. The combustor flow-path design was finalized based on the combustion test results. In addition, an ethylene fuel ignition method using pilot hydrogen injection, adopted for the flight experiment, was also demonstrated successfully.