Influence of injection positions on combustion performance in kerosene-fueled multi-cavity Scramjet combustor

The kerosene-fueled Scramjet with multi-cavity combustor has the potential to serve as propulsion system for hypersonic flight. However, the impact of injection positions on combustion performance and mechanism at high Mach numbers remains uncertain. Therefore, a comparative study was conducted using numerical methods to explore multi-cavity Scramjet combustor performance at a flight Mach number 7.0 with different injection positions. The combustor is equipped with 6 cavities arranged in three groups along the flow direction, each consisting of two cavities perpendicular to the flow. It is shown that the injection location significantly influences combustion performance: Front-injection yields higher combustion efficiency than post-injection, but post-injection is advantageous for the intake start. Additionally, regardless of injection positions, the mainstream flow state near the cavities behind the injection can be categorized as supersonic flow, supersonic-subsonic coexistence flow, and subsonic flow. The optimal length from the downstream to the trailing edge of the cavities behind the injection for achieving maximum combustion efficiency is determined. Further extension beyond this optimal length does not significantly increase the combustion efficiency. In addition, the optimal length varies with different injection positions − specifically, it is about 60% longer with post-injection conditions than with front-injection conditions in this investigation. Moreover, significant secondary combustion within the cavities leading to improved efficiency only occurs when mainstream flow state is either supersonic flow or supersonic-subsonic coexistence flow. Also, with a well-optimized design, the kerosene-fueled multi-cavity Scramjet can achieve enhanced combustion efficiency, which shows relatively small variation across a wide range of equivalence ratios. This might be caused by the effects of interaction among these multiple cavities. Therefore, these research findings can provide valuable insights for designing and optimizing the kerosene-fueled multi-cavity combustor in Scramjet at high Mach numbers.