Impact of Diluents on Flame Stability With Blends of Natural Gas and Hydrogen

Two potential decarbonization pathways for natural gas (NG)-fueled gas turbine engines include blending hydrogen (H-2) into NG and postcombustion carbon capture. H-2 blending changes several combustion properties, including flame speed and stretch sensitivity. The use of post-combustion carbon capture systems is typically facilitated by the implementation of exhaust gas recirculation (EGR), where exhaust gases are injected into the inlet of the engine, increasing carbon dioxide (CO2) concentration at the outlet and, hence, increasing the efficiency of carbon capture technologies. In this work, we explore the impact of H-2 blending and EGR on the stability of a swirl-stabilized, central-piloted flame. Mixtures of NG and H-2 are tested at a range of different diluent compositions, with oxygen varied from 21% to 15% by volume in the oxidizer. In all cases, a constant adiabatic flame temperature is maintained to mimic the operation of a gas turbine at a given turbine inlet temperature. A variable-length combustor is used for testing, where combustor length is varied to understand the dynamic stability characteristics of the system. Results show that EGR and H-2 work in opposition to each other, where higher levels of EGR result in poor flame holding and higher levels of H-2 result in better flame holding. Increasing H-2 generally increases the amplitude of thermoacoustic instability at each condition, a result of the change in flame position in this particular combustor. Importantly, H-2 can be added to NG to improve flame holding without significantly decreasing CO2 levels in the products, showing that H-2 blending can be a method for counteracting combustor operability issues that arise from high levels of EGR necessary to improve the efficiency of typical carbon capture systems.