Impact of Dilution Air Flow Rate Modulation on Exit Temperature of Gas Turbine Combustion Chamber

The management of exit temperature in gas turbine combustors is critical for ensuring turbine blade life, thermal efficiency, and operational flexibility. Dilution air injection is a primary method for cooling combustion products, yet the quantitative effect of modulating its flow rate on exit temperature remains insufficiently understood. This study employs a Computational Fluid Dynamics (CFD) approach using ANSYS FLUENT to investigate the impact of dilution air flow rate modulation on the exit temperature of a can‑type gas turbine combustion chamber operating under steady‑state conditions with methane fuel. A three‑dimensional model of the combustor was developed, and simulations were performed for dilution air mass flow rates ranging from 0.001 kg/s to 0.005 kg/s. Results show a strictly monotonic decrease in exit temperature with increasing dilution air flow, yielding a total reduction of 87 °C (approximately 4.0%) across the tested range. However, diminishing marginal cooling effectiveness is observed, with the largest reduction (43 °C) occurring between 0.001kg/s and 0.002 kg/s and progressively smaller reductions at higher flow rates. The midpoint exit temperature decreases by about 20 °C when dilution air is increased from 100% to 400% of baseline. The study quantitatively demonstrates that while increased dilution air flow significantly reduces thermal loading, benefits diminish beyond an optimal range (approximately 0.003–0.004 kg/s or a 200–250% increase). These findings provide design engineers with quantitative criteria for balancing exit temperature reduction against pressure loss, combustion efficiency, and flame stability.