Sea-level Static Tests of a Rocket-Ramjet Combined Cycle Engine Model

摘要

A rocket-ramjet combined cycle engine model, embedding twin rocket chamber on top wall side of a scramjet flow pass, was fabricated and was tested under sea-level, static conditions. The rocket chamber was driven with gaseous hydrogen and oxygen at nominal operation condition of 3 MPa in chamber pressure and 7.5 in mixture ratio. Gaseous hydrogen was also injected through secondary injector orifices to pressurize the ramjet combustor. Contraction in the inlet section was changed to investigate air ingestion performance, while a mechanical contraction mechanism with variable contraction ratio was installed near the exit of the engine to enhance pressure recovery within the diverging portion of the flow pass. Choking of the ingested airflow was not attained, and the airflow rate was 2/3 of the design value. Pressure-rise within the diverging portion of the flow pass was not intensive to attain choked condition at the engine exit. The mechanical contraction enhanced penetration of shock system associated with thermal and mechanical throttling at the engine exit, which in turn, enhanced mixing between the airflow and the rocket plume. However, the shock system penetrated further upstream on the airflow side with lesser total pressure, increased the back -pressure to the inlet section, resulting in reduced airflow rate. An excess injection of secondary fuel generated a shock system-like pressure rise, however, enhanced mixing was not sufficient to sustain pressure-rise through secondary combustion within the ramjet combustor with the excessive injection turned-off. Thus, enhancement of mixing between the airflow and rocket plume without help of the shock system is necessary for further thrust augmentation.