Experimental study of combustion instability and flame dynamics of hydrogen-enriched methane and pure hydrogen swirl flames

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Hydrogen-enriched combustion provides an important technical pathway for the low-carbon operation of gas turbines. However, adding hydrogen significantly alters flame dynamics and can easily induce thermoacoustic instability. Our study uses a partially premixed three-stage swirl burner to experimentally investigate combustion instability and flame dynamics in hydrogen-enriched methane and pure hydrogen swirl flames at hydrogen power ratios (HPRs) of 70%–100%. The macroscopic flame structure, oscillation dynamics, and thermoacoustic coupling characteristics were investigated using a combination of optical diagnostics and signal-processing techniques. The experiment identifies four typical flame morphologies: single detached compact flame, double detached compact flame, V-shaped attached flame, and jet stabilized flame. As HPR and methane equivalence ratio ( Φ C H 4 = 0.6–0.875) increase, the system shows significant nonlinear transition behavior, including behavior characteristic of subcritical bifurcation. It transitions gradually from stable combustion to low-amplitude limit cycle oscillations (LCOs), and then to high-amplitude LCOs. The pressure oscillation amplitude reaches about 2.7 kPa. This oscillation is dominated by the first-order axial acoustic mode and distinct harmonic components. Stability contour plots reveal the widest oscillation range at HPR = 90%. At HPR = 100%, the pure hydrogen flame returns to a stable combustion state at higher equivalence ratios, potential due to faster flame propagation and reduced vortex-flame interaction. Phase-averaged OH* images and SPOD analysis reveal the periodic evolution process of the flame core—formation, development, and extinction—and a dominant axially coherent structure. In summary, this study focuses on combustion instability and flame dynamics of fuel with more than 70% HPR, providing important experimental evidence for the stable operation of hydrogen-enriched methane gas turbine combustors.

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