Effects of Adiabatic Flame Temperature on Premixed Combustion Stability and Emission Characteristics of Swirl-Stabilized Oxy-Methane Flames

Effects of adiabatic flame temperature (AFT) on stability, combustion, and emission characteristics of swirl-stabilized premixed oxy-methane flames are investigated numerically in a model gas turbine combustor using large-eddy simulations. The oxy-methane flames are investigated over ranges of equivalence ratio (phi: 0.342-0.954), oxygen fraction (OF: 35%, 50%, and 65%), and adiabatic flame temperatures (AFT: 2100 K, 2300 K, and 2500 K) at fixed inlet velocity of 5.2 m/s with swirled flow at 55 deg under atmospheric pressure. The results show that the shape and size of the inner recirculation zone (IRZ) dominates the flame shape and flame-flow interactions whatever the operating AFT and OF. Almost identical flame shapes with similar OH distributions are obtained at fixed AFT indicating the dominant role of AFT in controlling flame shape and stability of premixed flames. At low to moderate AFTs, the IRZ spreads downstream and becomes stronger resulting in more flame stability and more uniform axial temperature profiles. Fixing the operating AFT does not result in significant changes in temperature profiles due to the similarity of shape and size of the IRZ when fixing the AFT. Flame core temperature, the thickness of the reaction zone, and vorticity increase with AFT at fixed OF and with OF at fixed AFT. The value of the Damkohler number increases in higher AFT and higher OF. Increasing the AFT from 2100 to 2500 K at OF = 65% resulted in an approximately 2.9 time rise in CO emissions.