Impacts of flow swirl on stability and flow/flame interactions of premixed oxy-methane swirl flames

Effects of flow swirl on stability and flow/flame interactions of premixed oxy-methane flames (CH4/O2/CO2) are investigated experimentally and numerically in a premixed model gas turbine combustor. Two swirlers of 55° and 45° swirl angles were considered to perform this study over a range of combustor operating equivalence ratio (Φ=0.1-1.0) and oxygen fraction (OF=21%-70%) at constant inlet flow velocity of 5.2 m/s. Combustor stability maps (representing flashback and blowout bounds) were identified experimentally in the Φ-OF space for the two swirlers and the results were plotted over the calculated contours of adiabatic flame temperature (AFT). Specific flames were photographed using a camera to investigate the impact of flow swirl on flame macrostructure. Also, the shapes of the selected flames were calculated numerically using the contours of OH radicals and the results showed good agreement with the photographed flame shapes. Contours of temperature and flow streamlines were plotted based on numerical calculations to figure out the influence of flow swirl on flame/flow interactions. The results showed that CH4/O2/CO2 swirl flames blow out at fixed AFT of ~1600 K with no effect of swirl on flame stability near the blowout. Flow/flame interactions significantly affect flame stability near the flashback limit. Flame speed (FS) and AFT correlate with one another as log(FS) ∝ 1/AFT. The 45° swirler resulted in a wider stable combustion zone than that of the 55° swirler.