Combustion Characteristics Analysis During Hydrogen-Ethylene Switching Process in Supersonic Flows

This study experimentally investigates the combustion mode transition and oscillation phenomena during hydrogen-ethylene fuel switching in a cavity-stabilized combustor with the inflow Mach number of 2.52. Reduced-order variational mode decomposition (RVMD) was used to identify the flame characteristics during mode transition in the upstream hydrogen-ethylene switching condition. The results reveal that no distinct mode transition is observed for the downstream hydrogen jet. In contrast, the upstream hydrogen jet significantly enhances combustion intensity and combustor pressure during the switching process, leading to a transition to the wake combustion mode. It is found that flame oscillations weaken during the hydrogen-ethylene co-combustion stage, whereas large-amplitude oscillations emerge after the switching process. This is attributed to the precombustion of upstream hydrogen during the switch to ethylene, which generates high-temperature zones and recirculation regions between these two jets. The enhanced combustion provides sufficient preheating to promote ethylene flame propagation, enabling the transition to the wake combustion mode. After hydrogen has been turned off, the disappearance of upstream recirculation weakens the ethylene flame, causing mismatched flame-flow interactions and resulting in significant oscillations.