Stratified Flames in Dual Annular Counter-Rotating Swirl Burner for Wider Operability Gas Turbines

This study investigates numerically the effects of equivalence ratio (Φ) on flow/flame interactions and emissions of stratified oxy-methane (CH4/O2/CO2) flames in a dual annular counter-rotating swirl (DACRS) burner for wider operability and environmental-friendly gas turbines. The flow mixture entering the combustor is split into two coaxial streams of different equivalence ratios. The central stream is characterized by higher Φ to continuously ignite the flame for enhanced flame stability, whereas the annular stream is a highly lean mixture to sustain the environmental performance of the combustor. The partially premixed combustion model is adopted in the ANSYS-FLUENT 2021-R1 software to model the reaction kinetics of the generated stratified flames in the two-dimensional axisymmetric domain. Nine cases of the same inlet velocity ratio (primary stream to secondary stream) of 3.0 are examined at a fixed oxygen fraction (OF: volumetric percentage of oxygen in the O2/CO2 mixture) of both streams of 30%. Flame stratification is achieved by varying the equivalence ratios of the primary (Φp=0.9, 0.8, and 0.7) and secondary (Φs=0.7, 0.55, and 0.4) streams. The results indicate effective flame/flow interactions, complete combustion, and reduced emissions for the DACRS stratified flames.