Effects of jet diameter and spacing in a micromixer-like burner for clean oxy-fuel combustion in gas turbines

The effects of jet diameter and spacing on flame structure and stability are examined in an oxy-methane micromixer-like burner for potential implementation in zero-emission gas turbines. Three burner headend geometries (HE1, HE2, and HE3) are compared at fixed flame-base velocity of 5.2 m/s and over ranges of equivalence ratio and oxygen fraction (O₂ vol% in the O₂/CO₂ oxidizer). HE1 has 61 jets of 3.175-mm diameter, arranged on a hexagonal matrix with a uniform jet spacing of 5.5 mm. HE2 has 37 jets of 3.970-mm diameter (25% increase), also arranged hexagonally with a spacing of 5.5 mm. HE2 has fewer jets to maintain almost the same combustor power. HE3 is similar to HE2, but with a jet spacing of 7.0 mm (27% increase). The three blowout limits were found to be only ∼45 K apart, despite the considerable differences in jet diameter and spacing, which demonstrates the remarkable geometry flexibility of micromixers. HE1 outperformed HE2 and HE3. Increasing the jet diameter adversely affects flame stability, because the burner deviates from the stable lean-direct-injection concept. Increasing jet spacing is also unfavorable. The adiabatic flame temperature is the primary parameter controlling the structure and stability of premixed methane flames for different burner geometries.