Control of unstable combustion oscillations in liquid-fueled gas turbines

A closed-loop controller to suppress thermoacoustic combustion instabilities in liquid-fueled systems is described. The controller supplies unsteady heat release pulses which are out-of-phase with those associated with combustion instability to damp unstable oscillations. Pulse-width modulation is used to control the heat pulse amplitude and phase. The controller was tested both in a numerical simulation of dynamic combustion instability using a 15 kW experimental laboratory combustor. The control system is being scaled-up for testing on a 200 kW model gas turbine combustor. Measurements of unsteady pressure and flame emission in the combustor indicate a strong thermoacoustic combustion instability near a frequency of 140 Hz for some operating conditions. The measured combustion dynamics as well as results from open-loop control experiments are described. The implications of the experimental results on closed-loop controller design are discussed.