On the effects of oxygen fraction on stability and combustion characteristics of dual-swirl oxy-methane flames: An experimental and numerical study

The effects of oxygen fractions of primary and secondary streams on flow/flame interactions, flame stability and macrostructure, and combustion and emissions characteristics of premixed oxy-methane (CH4/CO2/O2) flames were studied experimentally and numerically in a dual annular counter-rotating swirl (DACRS) burner for applications of clean power production in gas turbines. The primary stream oxygen fractions (OF_p) of 34 % and 25 % were paired with secondary stream oxygen fractions (OF_s) ranging from 25 % to 39 % at fixed primary stream equivalence ratio (φ_p = 0.9), fixed velocity ratio of 3.0 by the primary (of 5 m/s) and secondary (of 1.667 m/s) streams, and over ranges of secondary stream equivalence ratios (φ_s). The results showed that at OF_p = 34 % and OF_S = 39 %, the pilot flame supports a lean secondary flame down to φ_s = 0.434 at combustor global equivalence ratio (φ_g) of 0.467. Flame flashback concerns were not seen in the operative OF_s zone until the secondary stream reached stoichiometric operation (φ_s = 1.0). The widths and forms of the inner and outer recirculation zones (IRZ and ORZ) are not significantly affected by changes in OF. Reducing φ_g and OF_g resulted in decreases in Damköhler number (Da), laminar flame speed, and CO emissions.