Shape and stability characteristics of hydrogen-enriched natural-gas oxy-flames in a micromixer burner

This study investigated experimentally the effects of H₂-enrichment on premixed oxy-methane flames stabilized on a micromixer-like burner for clean energy production in gas turbines. The stable combustion zone was established over ranges of fuel hydrogen fraction (HF: 25–70% by vol.) and equivalence ratio (ϕ: 0.1–1) at fixed oxidizer oxygen fraction (OF = 30% by vol.) and fixed jet velocity (5.2 m/s). The blowout limit was plotted within the HF-ϕ space, superimposed on the contours of some operating parameters, namely adiabatic flame temperature (AFT), combustor power density (PD), jet Reynolds number (Re), and unburnt-mixture density (ρ_mix). Furthermore, images of visible flame shape were acquired at distinct points within the stable zone to study the effects of ϕ, HF, AFT, PD, Re, and ρ_mix on flame macrostructure. Results show that H₂-enrichment extends the blowout limit from ϕ = 0.35 down to ϕ = 0.1, thereby widening the stable combustion zone. The blowout limit has little correlation with AFT and PD but correlates strongly with ρ_mix, i.e., occurs consistently at the same ρ_mix. The analyses of blowout limit and flame images were used to infer that the flames blow out possibly at constant ignition delay.