Effect of Exhaust Gas Recirculation on Combustion Efficiency in a Swirl-Stabilized Flame With Blends of Natural Gas and Hydrogen

Abstract Reducing the carbon impact of power-generation and industrial gas turbines can be achieved through blending of low-carbon fuels as well as carbon capture. In gas turbines, carbon capture is facilitated by the use of exhaust gas recirculation (EGR), where exhaust gases are mixed with inlet gases to increase carbon dioxide concentrations in the exhaust, which in turn increase the efficiency of carbon capture technologies. However, increasing the diluent fraction of the reactants can decrease flame static stability and lead to flame elongation, potentially affecting combustion efficiency and emissions. In this study, we measure emissions in a single-nozzle model combustor at a range of EGR levels and compositions for blends of natural gas (NG) and hydrogen (H2) to understand the impact of EGR on combustion efficiency. Different blends of diluents that mimic the effects of EGR are tested with oxygen mole fractions from 21% (no diluent injection) down to 15%. Blends of NG and H2 are tested with up to 40% H2 by volume. Flame imaging is used to better understand the connection between EGR, fuel composition, flame stabilization, and combustion efficiency. As EGR level increases, the flame becomes longer and more diffuse. H2 blending aids flame stabilization and combustion efficiency. The experimental results are complemented by detailed chemical kinetic modeling to identify the changes in reaction pathways that are driven by such high levels of diluents and various fuel compositions. We conclude with a discussion of the impact of low combustion efficiency on both cycle efficiency as well as the performance of downstream carbon capture systems.