Active Control of Combustion Oscillations by Non-Coherent Fuel Flow Modulation

Abstract

This paper describes the application of active, open loop, control in effective damping of severe (i.e., peak to peak pressure amplitudes of up to 35 psi relative to a mean combustor pressure of 155 psi) combustion instabilities in a gas turbine combustor simulator. Active control was applied by harmonic modulation of the fuel injection rate into the combustor using a fast response actuating valve. To determine the dependence of the performance of the active control system upon the frequency, the fuel injection modulation frequency was varied between 50 and 500 Hz while the frequency of instability was around 386 Hz. These tests showed that the amplitude of the combustor pressure oscillations varied ten fold over the range of investigated frequencies, indicating that applying the investigated open loop control approach at the appropriate frequency could effectively damp detrimental combustion instabilities. When the same active control system was operated in closed loop with an optimized control signal phase at the frequency of instability, the amplitude of the unstable oscillations was reduced by a factor of two, thus causing the combustor to operate with lower amplitude instability.