Numerical Analysis of Scramjet Mode Operation of a RBCC Engine

In this study, numerical analysis was conducted for the scramjet mode operation of a JAXA rocket/ramjet combined cycle engine called E3 under Mach 8 flight conditions. The objective of the study is to examine the effects of rocket chamber pressure Pc and secondary fuel injection on the engine performance and related flow physics before the engine combustion tests. The calculation results revealed that the engine produced higher specific impulse Isp as well as thrust with higher Pc. However, the net thrust acting on the internal ramjet duct wall was smaller than the embedded rocket thrust. This is due to the fact that the rocket exhaust increased the friction drag on the combustor walls over the thrust due to combustion with the captured air. On the other hand, the secondary fuel injection in the diverging combustor had almost no impact on the thrust augmentation. This partially comes from that at lower Pc the combustion efficiency was much lower than expected because of the lower temperature and larger amount of H radical production in the combustor air flows. In addition, an auxiliary fuel injector was tested to examine the effects on combustion enhancement for the rocket residual fuel. A small thrust gain was found by using this injector.