An Investigation of the Effects of Fuel Staging on Flame Structure in a Gas Turbine Model Combustor

Abstract

Gas turbine (GT) flames at lean operating conditions are susceptible to instabilities that can lead to unsteady operation, flame extinction, and thermoacoustic oscillations. High speed (10 kHz) laser and optical diagnostic techniques have been used to investigate the effect of fuel staging on the mechanisms involved in such instabilities and the overall performance of a gas turbine model combustor. The GT burner used in this study consists of coaxial swirlers which allow for fuel staging capability, where the fuel is varied from 100% to 20% fuel injection in the inner swirler. The burner is equipped with a combustion chamber with large quartz windows, allowing for the application of optical and laser diagnostics. Simultaneous high speed OH Planar Laser Induced Fluorescence (PLIF) and OH* chemiluminescence (CL) imaging, exhaust gas sampling and acoustic measurements were applied to characterize the flames and determine the operability limits of the combustor. Methane air flames at atmospheric pressure have been investigated at a constant thermal power of 58 kW. The global equivalence ratio was kept constant, while the fuel staging was varied. The bulk flow velocity at the exit plane was kept constant at 20 m/s. Simultaneous high speed particle image velocity (PIV) and OH PLIF measurements were performed at a repetition rate of 10 kHz on specifically chosen flames with a fixed staging and equivalence ratio. This paper will present the flame and the flow field structure resolved using the kHz measurement technique. The interaction between the velocity field and the flame front marked by the OH LIF will be presented. The mean PIV image provides the location of the inner and outer recirculation zones. The flame structure presented in this paper will also show the effectiveness of fuel mixing as the staging is varied. The changes in flame shape with variation in fuel staging is determined using the OH* chemiluminescence images. As the fuel flow in the inner swirler is reduced, the NOx and CO emissions also reduce and reach a minimum at a staging of 45% fuel being injected in the inner swirler. As fuel injection in the outer swirler increases beyond 60% the NOx and CO emissions start also increasing.

Phase Resolved Analysis of Flame Structure in Lean Premixed Swirl Flames of a Fuel Staged Gas Turbine Model Combustor

“…A detailed description of the experimental setup is presented by Gounder et al (2013). All experiments were conducted using a conceptual burner designed for gas turbine application.…”

“…The present work is the continuation of our study (Gounder et al, 2013) of fuel staging effect on the flame structure, stabilization mechanism, and thermo-acoustic instabilities in methane air flames at atmospheric pressure. A detailed description of the operability limit of the burner has been presented by Gounder et al (2013); therefore a summarized version of the burner characterization and initial conditions are provided here.…”

“…Out of the six staging ratios presented in Table 1, an optimum ratio was determined based on the minimum CO and NOx measured in the exhaust of the respective flames. The optimum staging ratio for this burner configuration was 1.8 (Flame 55/45) as shown by Gounder et al (2013) …”

“…A detailed description of the operability limit of the burner has been presented by Gounder et al (2013); therefore a summarized version of the burner characterization and initial conditions are provided here. The bulk exit plane velocity for all flames investigated was kept constant at 20 m/s.…”

“…High-speed (10 kHz) planar laser induced fluorescence (PLIF) of OH and OH * chemiluminescence (CL) and acoustic measurements were performed to investigate the effect of fuel staging on lean premixed flame behavior. Flame characterization measurements presented in (Gounder et al, 2013) are analyzed using phase resolved analysis.…”