Extreme fuel-rich combustion characteristics of RBCC embedded rocket engine with gas-liquid shear coaxial injectors in continuously varying mixture ratios

In order to achieve stable and effective transition between the operation modes in a rocket-based-combined-cycle engine (RBCC), the embedded rocket engine should be capable of throttling continuously in a wide range of operation conditions. A kerosene/GO₂ RBCC embedded rocket engine with gas–liquid shear coaxial injectors was designed to investigate the combustion characteristics under varying operation conditions. Throttling cold test, static hot test, and throttling hot tests in varying mixture ratios (0.102–0.221) were conducted with a throttleable venturi and a throttleable sonic nozzle. In these tests, the mixture ratio was adjusted in two ways: one is to linearly decrease the fuel mass flow rate with a constant oxygen mass flow rate, and the other is to increase the oxygen mass flow rate with a constant fuel mass flow rate. Results indicate that the combustion efficiency and the characteristic velocity increase along with the mixture ratio, but show a different growth rate depending on the mixture ratio adjustment method. To specify, characteristic velocity and combustion efficiency of hot test throttled by increasing oxygen mass flow rate grow faster. And in the range of mixture ratios (Φ<0.25), the combustion efficiency obtained by both adjustment methods is lower than 55%. The flame behaviors are influenced significantly by the oxygen mass flow rate, and a reasonable explanation is that increasing oxygen mass flow rate can significantly increase the spray angle and decrease the mean diameter. And the flame behaviors can influence the discharge coefficient of the kerosene injector. Furthermore, the discharge coefficient decreases along with the decrease of kerosene mass flow rate in both hot and cold tests.