Numerical analysis supported with experimental measurements of premixed oxy-propane flames in a fuel-flex gas turbine combustor

The combustion, exhaust-gas concentrations, and stability characteristics of premixed CO₂-diluted oxy-propane (C₃H₈/O₂/CO₂) flames were investigated computationally using large eddy simulations (LES) in a swirl-stabilized model gas-turbine combustor. The simulations were carried out for ranges of equivalence ratio (Φ: 0.26-0.80) and oxygen fraction (OF: 35%-60%) at a fixed bulk inlet velocity of 5.2 m/s. The results indicate that the reaction rates increase with the increase of Φ and OF. Flames of the same adiabatic flame temperature (T_ad) show similar macro-and flowfield-structures, in terms of flame shape, flow circulation, and temperature, and species distributions, irrespective of the values of Φ and OF. At higher T_ad, the flames were observed to be more compact with reduced flame thickness and higher Damkohler number (Da). In all cases, Da > 1 were observed, indicating the dominance of reaction rate in oxy-propane flames than the diffusion rate. A secondary IRZ was also observed near the outlet of the combustor. Mixture composition and combustion temperature influence the CO concentration at the combustor exit. The highest CO emission was observed at 0.17 ppm for the flame with highest Φ and T_ad, meanwhile no CO emission was seen for flames with high OF and low Φ among the studied cases. Highlights: Adiabatic flame temperature is a quantifying parameter for flame characterization. The outer recirculation zone plays a vital role in flame anchoring/stabilization. Primary inner recirculation zone has several eddies controlled by the equivalence ratio. Secondary inner recirculation zone was also observed near the combustor outlet. Elevated CO emission was observed at high equivalence ratio and low oxygen fraction.