Transient Cavity Ignition And Periodic Flame Stabilization Modes In Rectangular Supersonic Flowpath

This paper examines the time-resolved dynamics of flame stabilization in a rectangular supersonic flowpath with a cavity. The ACT-II arc-heated blowdown wind tunnel at the University of Illinois Urbana-Champaign was used in a direct-connect configuration to observe high-speed time-resolved wall pressure measurements and color broadband imaging of combustion at a total pressure of 2.1 bar and total temperature of 1450 K. A 50:50 mixture by volume of hydrogen and ethylene was injected both upstream in the isolator and on the takeback ramp of the cavity for a global equivalence ratio of 1 in the flowpath at an oxygen mass fraction of 0.46. Wall pressure measurements at 20 kHz and color images at 25 kHz show strong acoustic vibrations and periodic motion of the flame in the axial direction. By demonstrating the strong flameholding effects in the flowpath, the effectiveness of the cavity is verified. A strong periodic motion of the flame between jet wake and cavity shear layer stabilization modes is observed, which is explained as an effect of robust mixing and heat release downstream of the cavity causing thermal choking. Results show that for a given fueling condition, two flame stabilization modes can exist and oscillate between each other.