Influence of Fuel Staging on Thermo-Acoustic Oscillations in a Premixed Stratified Dual-Swirl Gas Turbine Model Combustor

In several technical combustion systems for lean, premixed combustion, mixture stratification plays an important role, such as in stationary and aero gas turbines. The current paper focuses on a detailed characterization of a dual-swirl gas turbine model combustor operated in a stratified regime. The influence of mixture stratification on flame stabilization and self-induced thermo-acoustic oscillations was studied using laser and optical diagnostics in combination with microphone probes to measure pressure oscillations in the plenums and combustion chamber. The overall flame-shape was imaged using OH* chemiluminescence. Laser Raman scattering was applied to study the thermo-chemical state of the flame, the flow-field was measured using Particle Image Velocimetry and pressure oscillations in the combustion chamber and in the air plenums were determined by using calibrated microphone probes. OH planar laser-induced fluorescence was used to determine fluctuations of the hot gas with high spatial resolution. Significant mixture stratification within the combustion chamber was found to only occur at or upstream of the flame root. Varying the stratification level did not significantly influence the mean flame shape and flow field, however, a clear influence on thermo-acoustic oscillations was observed.