Numerical Investigation of High CO2 Dilution Effects on Methane-Hydrogen Flame Structure in Turbulent Swirl-Stabilized Flames

Lowering carbon emissions while meeting the demand for industrial power generation is a matter of great importance. Combustion of H2 fuels and high-H2 fuel blends has attracted interest in addressing this concern, especially due to the potential for use with minimal system re-design. To increase the efficiency of the carbon removal process from the exhaust, as well as to reduce the NOx emissions which increase with H2 addition, CO2 may be used as a diluent in industrial combustion strategies utilizing exhaust gas recirculation (EGR), whereby a portion of the hot gases exiting the combustor are mixed in with the unburned reactants. In the present study, we perform high-fidelity large eddy simulations (LES) of a simplified annular combustor geometry using the highly scalable spectral element code Nek5000 to capture the effects of varying levels of CO2 dilution on the flame structure, turbulence statistics and stability in the lean combustion regime near the blowoff limit. While flames can burn hotter and faster with higher H2 percentages in the fuel stock, increasing CO2 dilution has the opposite effect, decreasing flame stability and lowering blowoff limits of swirl-stabilized flames such as those found in typical combustors. In our numerical experiments, we investigate the flame and flow behavior in this highly diluted regime, using detailed chemical kinetics to enable new insights into distribution of key species, which play an integral role in the behavior of the flame under highly strained conditions.