Effect of Inert Species on the Static and Dynamic Stability of a Piloted, Swirl-Stabilized Flame

Carbon sequestration and utilization has been proposed as a method for decarbonizing highefficiency industrial gas turbines operating on natural gas fuels for power generation and industrial markets. To increase the efficiency of the carbon removal process from the exhaust stream of the turbine, exhaust gas recirculation (EGR) can be used. EGR recycles a portion of the engine exhaust into the inlet, increasing the concentration of inert species in the exhaust stream to improve the performance and cost-effectiveness of CO2 separation systems. This strategy can, however, reduce the oxygen concentration in the air, leading to changes in flame stabilization in the combustor. In this study, we investigate the effect of air diluted with inert gases of different compositions and the impact that these mixtures have on flame static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variablelength combustor is used to measure the flame behavior for oxygen concentrations of 15-21% by volume. A constant adiabatic flame temperature test matrix is conducted to mimic operation in an industrial gas turbine. High-speed chemiluminescence imaging is used to determine the change in flame shape and dynamics for each gas composition. As the oxygen concentration decreases, the flame lifts from the centerbody, resulting in an aerodynamically stabilized flame at the lowest O2 concentrations. Different compositions of gases result in different flame shapes, where higher levels of N2 in the diluents result in more flame stabilization in the outer recirculation zone as compared to those with higher levels of CO2. The flame oscillation mechanisms also change with oxygen concentration, where the lifted flames at lowO2 levels exhibit an ignition/extinction oscillation mode as compared to a vortex-shedding-coupled oscillation mode at high O2 levels where the flame is stabilized on the centerbody. Companion chemical kinetics simulations are used to explain changes in the flame's shape and behavior.