Combustion Oscillations in Scramjet Combustor with Different Fuel Injection Schemes

This work experimentally studied combustion oscillations in a cavity-based combustor operating under high-enthalpy supersonic flow. Three fuel-injection distances and the corresponding combined fuel injection schemes were tested and compared with the global equivalence ratio unchanged. The results indicate that the combustions of longer and medium distances (35 and 21 mm, respectively) present stronger oscillations, which are mainly attributed to the strengthened oscillations of the mainstream flame (MF). It is also found that combined fueling schemes can help weaken the oscillations. The predominant frequencies of the combustion oscillations in different fueling schemes are all distributed at approximately 400 Hz, which are proven to be induced by the MF. The low-frequency range (0–50 Hz) is more dominant for the shorter injection distance (7 mm) than in the other cases, which is because the flames are strongly influenced by low-frequency disturbances with fluctuations in the fueling injection and inflow. The analysis reveals that these disturbances act primarily on the cavity flame.