Experimental investigations of combustion oscillation modes in a large-aspect-ratio dual-mode combustor equipped with multi-strut

The annular scramjet combustor is considered one of the best configurations for a wide-speed-range combined engine, owing to its superior thermal protection performance and optimal geometric compatibility with rockets and turbines. To investigate the effect of fuel injection methods on the flame oscillation characteristics in the annular combustor, a scaled-down experiment was conducted on a fan-shaped combustor with a high aspect ratio equipped with multiple struts, utilizing liquid kerosene as the fuel. A series of experiments were conducted at the combustor inlet conditions of Ma=2.7, P-t=1.68MPa, and T-t=1640K. High-speed cameras and pressure measurements were used in the experiments, and the flame images were processed using proper orthogonal decomposition. The findings revealed that under single-strut and multi-strut injection conditions, the flame oscillated in two modes: shear layer oscillation and central flame oscillation. As the equivalent ratio of injection strut increased, the oscillation frequency increased from 25 to 284Hz, and the oscillation mode transition caused by the adverse pressure gradient occurred. The flashback was closely related to the combustion mode, and the distinct flame propagation processes under supersonic and subsonic flow conditions resulted in different oscillation characteristics. The experiment demonstrated that the flashback issue could be mitigated by increasing the spacing between the fuel injection struts. The study in this paper will provide important references for future research on flame oscillation and propagation characteristics in high-aspect-ratio annular combustors.