A comparison of the flowfields and emissions of high-swirl injectors and low-swirl injectors for lean premixed gas turbines

A new approach for low emission gas turbines was investigated by modifying a typical production high-swirl injector (HSI) for gas turbine combustors to operate in a novel low-swirl mode (LSI). This LSI (S = 0.5) was configured in the laboratory and investigated by particle image velocimetry at firing rates of 9-87 kW (1 < U-0 < 10 m/s). It was also tested at simulated gas turbine conditions of 0.08-2.2 MW (20 < U-0 < 50 m/s) at elevated combustion inlet temperatures (230 < T-0 < 430 degrees C) and pressures (6 < P-0 < 15 atm). The results were compared with those obtained with a HSI (S = 0.73). The PIV results show that the flowfields of the LSI are devoid of a large dominant recirculation zone. This is fundamentally different than the strong and large recirculation regions that dominate flowfields of the HSI. Under simulated engine conditions, the LSI has the same operating range as the HSI. Its NOx emissions were about 60% lower than the HSI, and its CO emissions were comparable. The lack of a strong recirculation zone and the shorter residence time within the LSI may provide an explanation for the NOx reduction. These results demonstrate that the LSI is a promising solution for attaining an ultra-low emissions target of < 5 ppm NOx (15% O-2) in gas turbines. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.