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

Abstract Carbon sequestration and utilization has been proposed as a method for decarbonizing high-efficiency gas turbines operating on natural gas fuels. To increase the efficiency of the carbon removal process, 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 reduce the oxygen concentration in the air, leading to changes in flame stabilization. In this study, we investigate the effect of air diluted with inert gases and the impact that these mixtures have on static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variable-length combustor is used to measure the flame behavior for oxygen concentrations of 15% to 21% by volume. A constant 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, 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 low O2 levels exhibit an ignition/extinction oscillation mode.