Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine

Abstract

During the prototype shop tests, the Model V84.3A ring combustor gas turbine unexpectedly exhibited a noticeable “humming” caused by self-excited flame vibrations in the combustion chamber for certain operating conditions. The amplitudes of the pressure fluctuations in the combustor were unusually high when compared to the previous experience with silo combustor machines. As part of the optimization program, the humming was investigated and analyzed. To date, combustion instabilities in real, complex combustors cannot be predicted analytically during the design phase. Therefore, and as a preventive measure against future surprises by “humming,” a feedback system was developed which counteracts combustion instabilities by modulation of the fuel flow rate with rapid valves (active instability control, AIC). The AIC achieved a reduction of combustion-induced pressure amplitudes by 86 percent. The Combustion instability in the Model V84.3A gas turbine was eliminated by changes of the combustor design. Therefore, the AIC is not required for the operation of customer gas turbines.

On the dynamic nature of azimuthal thermoacoustic modes in annular gas turbine combustion chambers

“…Several numerical, experimental or theoretical studies have been dedicated to these azimuthal thermoacoustic modes over the last decade in order to better understand and control them to further increase the operational flexibility of the gas turbines. Based on practical observations, Krebs et al [3] and Seume et al [4] concluded from time-averaged measurements that both dominantly standing or rotating modes can be found depending on the gas turbine operating conditions or burners arrangement. Other studies carried out using loworder thermoacoustic network simulations [5][6][7][8] or deriving nonlinear analytical models [6,9] shed some light on the dynamic nature of the azimuthal modes.…”

Multivariable adaptive control of instabilities arising in jet engines

“…A simple phase-shifting controller with an appropriately chosen phase-shift was typically sufficient for suppression of oscillations, given enough control authority, but the control phase and gain had to be adjusted manually, at every operating condition. The difficulty in determining the optimal phase shift that minimizes pressure oscillations, either by analysis or by experiment, especially in large industrial-scale combustors that operate over a wide range of conditions, has led researchers to call for the use of adaptive schemes (Seume et al, 1997). A direct adaptive scheme (based on extremum-seeking) applicable to control of thermoacoustic modes with large separation in frequencies (and hence essentially decoupled) was recently demonstrated in a 4 MW industrial rig in Banaszuk, Ariyur, Krstic, and Jacobson (2004).…”

“…Control of thermoacoustic instabilities using high speed fuel valves and pressure sensors was demonstrated in numerous experiments in academia and industry (Candel, 1992). Including a demonstration on a full scale industrial gas turbine (Seume et al, 1997). A simple phase-shifting controller with an appropriately chosen phase-shift was typically sufficient for suppression of oscillations, given enough control authority, but the control phase and gain had to be adjusted manually, at every operating condition.…”

Minimizing transient energy growth of nonlinear thermoacoustic oscillations

“…Generally, there are two typical actuation actions. One is to vary the unsteady heat release rate by using a secondary fuel or air injector [28,29]. For example, a secondary air injector was used [30] to stabilize a lean premixed pre-vaporized swirl-involved combustor.…”