Manifestations of Combustion Instability in a Multi-swirl Stabilized Gas Turbine Combustor

This paper is on study of manifestations of combustion instability in a multiple swirl low emission gas turbine combustor. Unstable combustion was investigated in different combustor setup, including with or without premixing section, and with gaseous and liquid fuel via measurement of dynamics of pressure, flame, and radical emissions. A set of four optical fibers integrated inside the multiple swirler fuel injector assembly monitored the local active radical emissions to provide phase information on unsteady flame dynamics. The acoustic pressure signal from a microphone is conditioned as the trigger signal for phaselocked OH* chemiluminescene imaging of the global flame. The flame dynamics are shown to be in different format for different geometries and types of fuel. The motions of flame front are shown to be closely related to the combustion instability driving mechanism, either periodic large flow structures or pulsation in fuel line. Analysis on transition from unstable to stable combustion reveals that the advantage of better mixing with gaseous fuel is offset by the faster growth rate of pressure oscillation. It was also found in this paper that the oscillations of pressure lead flame in both gaseous fuel and spray combustions when unstable combustion takes place.