Control of Thermo - Acoustics Instabilities : The Multi - Scale Extended Kalman Approach NASA / TM — 2003 - 212536 / REV 1 October 2003 AIAA – 2003 – 4934

However, these other means (e.g., speaker actuation) tend to be bulky, have limited operating range, or have other undesirable side effects. In comparison, liquid fuel modulation is compact, more practical, and can deliver the most energy with the least effort. based control approach recently found to be effective for suppressing combustion instabilities in gas turbines. A control law formulated in this approach for fuel modulation demonstrated steady suppression of a high-frequency combustion instability (>500Hz) in a liquid-fuel combustion test rig under engine-realistic conditions. To make-up for severe transport-delays on control effect, the MSEK controller combines a “wavelet”-like “Multi-Scale” analysis and an “Extended Kalman Observer” to predict the thermo-acoustic states of combustion pressure perturbations. The commanded fuel modulation is composed of a damper action based on the predicted states, and a tones suppression action based on the Multi-Scale estimation of thermal excitations and other transient disturbances. The controller performs automatic adjustments of the gain and phase of these actions to minimize the Time-Scale Averaged Variances of the pressures inside the combustion zone and upstream of the injector. The successful demonstration of Active Combustion Control with this MSEK controller completed an important NASA milestone for the current research in advanced combustion technologies. The NASA Glenn Research Center (GRC) Active Combustion Control (ACC) technology effort aims to demonstrate active control in a realistic and relevant environment by providing experiments tied to aircraft gas-turbine engines. The first successful demonstration of active control of a High Frequency (HF; >500Hz) thermo-acoustic instability via fuel modulation under engine-realistic conditions was accomplished in June 2002 by the NASA GRC effort. It was reaffirmed in September 2002 with additional experiments and improved results. These experiments were done in collaboration with Pratt Whitney 14,15,16 at the United Technology Research Center (UTRC), on the NASA Single Nozzle Combustion Rig (SNR). Prior to this work, partial successes with suppression via fuel modulation of Low Frequency instability (LF; ~280 Hz) had been reported elsewhere, including the works supported by NASA. In these earlier attempts to suppress the dominant instabilities, other instability peaks would arise around the central frequency (so-called “peak splitting” as seen on the pressure amplitude spectra plot, Figure 1). A solution to this problem, which occurs even with moderate control gains, has not been identified in previous works 8, ..., . For this effort, active instability suppression has been demonstrated for high-frequency oscillations on the NASA SNR. This HF