Performances of a Rocket Chamber for the Combined-cycle Engine at Various Conditions

A gaseous hydrogen/gaseous oxygen rocket chamber was designed to fit in a rocketramjet combined-cycle engine model, and its performance was evaluated experimentally. Such a rocket chamber is required to operate in very wide ranges of chamber pressure (Pc) and mixture ratio (O/F). For stable operation, the injector has a choking point and a diffuser in the downstream portion. The design point of the injector is Pc = 5.0 MPa and O/F = 7 when the injection pressure of both the fuel and the oxidizer is 7 MPa. Stable operation and a C-star efficiency of 0.91 were attained in the rocket mode operation at O/F = 6.5 - 7.5 and Pc = 3 - 5 MPa. Stable operation and a C-star efficiency of 0.93 were attained in the ramjet mode operation at O/F = 4.5 - 7 and Pc= 0.6. This stable operation was attained by supplying oxygen from two, three or four of eight injectors. The C-star efficiency was 0.94 with four oxygen injector elements at O/F = 0.89, and 0.92 with three oxygen injector elements at O/F = 0.49. No thermal damage was observed on the oxygen post and faceplate with flush face oxygen post in all operating conditions. The fundamental design of the rocket chamber and injector for the combined-cycle engine was completed in this study.