Combustion dynamics and instability suppression in a methane/oxygen double-slit pintle injector

The combustion dynamics and stability mechanisms of a methane/oxygen double-slit pintle injector are experimentally investigated using dynamic pressure measurements and high-speed OH* chemiluminescence images. Across various combustor lengths and mixture ratios, longitudinal acoustic pressure fluctuations are remarkably weak, with amplitudes not exceeding 0.8% of the average pressure. Analyses show that these fluctuations result from the hydrodynamic vortex shedding of the axial methane jet and scale consistently with the Strouhal number. Furthermore, Dynamic Mode Decomposition and local Rayleigh index distributions indicate that the double-slit geometry spatially decouples heat release across the combustor, independent of the mixture ratio. As the convecting methane reacts sequentially with oxygen from the two separate slit rows, it distributes heat release into counteracting upstream instability-driving and downstream instability-damping regions. This spatial phase separation effectively mitigates the overall acoustic amplitude.