Effect of Oxygen Content on Combustion Stability in a Staged Swirl Combustor Under Various Operating Conditions

Flue gas recirculation (FGR) is an effective technique for reducing thermal nitrogen oxide (NOx) emissions of gas turbines. However, variations in inlet oxygen concentration significantly alter the internal combustion characteristics of staged swirl combustors and induce combustion instability. To clarify the coupling mechanism between oxygen content and combustion stability under diverse operating conditions, three-dimensional numerical simulations are performed on a staged swirl combustor. The effects of oxygen mass fraction ranging from 11% to 23%, together with multiple operating parameters including inlet temperature, inlet velocity and operating pressure, on flame morphology, velocity fluctuation, heat release fluctuation and pressure fluctuation, are systematically investigated. The results show that increasing the inlet temperature optimises the uniformity of heat release, compensates for the combustion inhibition under low-oxygen conditions, and effectively improves combustion stability. Oxygen content exhibits a non-monotonic regulatory effect on combustion pulsation characteristics. Appropriate reduction of oxygen content narrows the high-temperature reaction zone and suppresses pressure fluctuations, thereby improving combustion stability, whereas a moderate low-oxygen condition of 17% aggravates velocity fluctuations and deteriorates combustion stability. Although elevated oxygen content enhances the overall heat release intensity, it increases the amplitude and dominant frequency of heat release fluctuations, which triggers combustion instability. Furthermore, high inlet velocity and high operating pressure amplify the disturbance of low-oxygen environments on the flame field and further degrade combustion stability. This study clarifies the competitive and coupling relationships among oxygen concentration, operating parameters and combustion dynamic characteristics, providing a theoretical basis for the stability optimisation and low-oxygen combustion regulation of gas turbine combustors with flue gas recirculation.