Le LI, Jiajian ZHU, Minggang WAN, Yifu TIAN, Tiangang LUO, Qinyuan LI, Shuaijia SHAO, Mingbo SUN

DOI Number: 10.60853/he6s-7r37

Conference number: HiSST-2024-00184

This work aimed to investigate combustion mode transitions in a cavity-based scramjet combustor. The experiments were carried out on a direct-connected facility with an inflow condition of Mach number 2.52, total pressure of 1.35 MPa, total temperature of 1650 K and total flow rate of 1 kg/s. The fuel injector consisted of two injection ports: fuel was continuously injected from one port while the other controlled the fuel flow for mode transitions by switching it on or off. High-speed schlieren and CH* imaging were used to characterize the dynamics of combustion mode transitions. Results showed that the back pressure in the scramjet combustor rose with the increasing combustion heat
release, causing the oblique shock wave in supersonic combustion mode to shorten and move forward. Then an oblique shock train was formed above the cavity, marking it as a dual-mode supersonic combustion mode. As the back pressure continued to rise, the shock train was expelled from the combustor, indicating a subsonic combustion mode. During this process, the flame was intensified and shifted upstream, transitioning from shear-layer stabilization to jet-wake stabilization. The mode transition was accompanied by shock and flame oscillations. In the supersonic-to-dual transition, the reflected shock wave oscillated above the cavity. In the dual-to-supersonic transition, the oblique shock wave at the injection position alternately appeared and disappeared, causing the shock train to weaken and strengthen repeatedly. When the transition occurs between the dual combustion mode and the subsonic combustion mode, the shock train oscillated in the upper left corner of the field of view, with the combustor alternating between shock train and non-shock states. The flame heat release zone underwent cycles of merging and decomposing during these transitions. In addition, it was observed that suddenly increasing the fuel injection could temporarily suppress the combustion.

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In Categories: 1.Events, HiSST 2024, Propulsion Systems and Components
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