Experimental investigation on performance variation and dynamic characteristics of a variable geometry rocket-based combined cycle combustor

Variable geometry combustor technology is a novel technical approach for enhancing the performance of rocket-based combined cycle (RBCC) engines. This research paper investigates the performance variation and dynamic characteristics of an RBCC combustor with variable geometry under Ma4 condition through ground direct-connect experiment. The thrust variation and the pressure dynamic characteristics of the combustor are obtained. The study shows that: (1) Increasing the height of the geometric throat improves combustor's flow condition. Off-axial flow can be rectified, directing it to the axial direction of the combustor. (2) Under the condition of Ma4, the combustor's thrust alters as the throat height rises. The peak thrust is achieved when the throat height reaches 2.16H, resulting in a 9% thrust increase. (3) The higher throat height is not conducive to the proper combustion organization of the combustor and can potentially cause combustion instability. (4) The increase of throat height and the response of pressure is almost synchronous. The pressure peak propagates periodically from the downstream to the upstream of the combustor, with a propagation period of approximately 6 ms. These findings suggest that in order to ensure stable combustor operation, the geometric throat height should be confined within a specific range. Increasing the throat height within this range enables control of flow characteristics, pre-combustion shock train's position, and the thrust performance of the combustor.