Enhanced lean blowout and macrostructure characteristics of stratified CH4/H2/O2/CO2 flames in a dual annular counter-rotating swirl combustor

This experimental study investigates the effects of hydrogen and oxygen fractions on stability and combustion characteristics of oxy-methane flames in a dual annular counter-rotating swirl combustor for wider operability of emission-free gas turbines. The pilot stream, comprising a mixture of H2 and CO2, serves as the pilot flame, while the mainstream, consisting of a mixture of CH4, CO2, and O2, is the dominant flame. The experiments were conducted at a fixed velocity ratio of 2.27 across a range of mainstream equivalence ratio. The results demonstrated that increasing hydrogen and oxygen fractions significantly enhanced the combustor's lean blowout stability. At hydrogen fraction of 15% and oxygen fraction of 34%, the blowout equivalence ratio was reduced to 0.35, compared to 0.50 at zero hydrogen enrichment, representing a ∼ 43% decrease. The highest temperature of 1763°C was recorded at equivalence ratio of 0.73, showcasing enhanced combustion intensity at richer equivalence ratios. Comparatively, at oxygen fractions of 34% and 30 %, with hydrogen fraction of 15%, the CO emissions dropped to a range of 2 to 4 ppm at equivalence ratio of 0.63, significantly lower than 33 ppm recorded at oxygen fraction of 26% and zero hydrogen enrichment. Flame imaging revealed that the flames became brighter, more compact, and stable with increasing hydrogen and oxygen fractions. These findings underscore the synergistic role of hydrogen and oxygen enrichment in extending lean blowout limits, improving thermal performance, and reducing emissions in dual annular counter-rotating swirl combustors.