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

This study investigated experimentally the effects of H-2-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 (phi: 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-phi 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 (rho(mix)). Furthermore, images of visible flame shape were acquired at distinct points within the stable zone to study the effects of phi, HF, AFT, PD, Re, and rho(mix) on flame macrostructure. Results show that H-2-enrichment extends the blowout limit from phi = 0.35 down to phi = 0.1, thereby widening the stable combustion zone. The blowout limit has little correlation with AFT and PD but correlates strongly with rho(mix), i.e., occurs consistently at the same rho(mix). The analyses of blowout limit and flame images were used to infer that the flames blow out possibly at constant ignition delay.