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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Active Instability Control: Feedback of Combustion Instabilities on the Injection of Gaseous Fuel

[+] Author and Article Information
M. P. Auer, C. Gebauer, K. G. Mösl, C. Hirsch

Lehrstuhl für Thermodynamik,  Technische Universität München, 85747 Garching, Germany

T. Sattelmayer

Lehrstuhl für Thermodynamik,  Technische Universität München, 85747 Garching, Germanysattelmayer@td.mw.tum.de

J. Eng. Gas Turbines Power 127(4), 748-754 (Mar 01, 2004) (7 pages) doi:10.1115/1.1924718 History: Received October 01, 2003; Revised March 01, 2004

Modern low-emission premix combustion systems are often susceptible to combustion instabilities. Active instability control (AIC) systems are commonly used to attenuate these oscillations. For the control authority of AIC systems the effective amplitude and phase of the fuel modulation at the fuel outlet are as critical as the proper injection position. In typical cases the modulation of the fuel at the location of the actuator can be fundamentally different in amplitude and phase from the modulation of the fuel flow at the fuel outlet. In addition to the well-known effects stemming from the acoustics and Mach number of the fuel system, the fuel flow in the fuel system is also modulated by the oscillation of the pressure in the combustor in case of combustion instabilities. The superposition of the upstream modulation by the actuator and the modulation downstream by the combustion instability can result in an unexpected behavior of the fuel injection, from total compensation of the modulation to very high oscillations in the resonant case, accompanied by drastic phase shifts. This paper describes the influence of the secondary fuel modulation because of the combustion instability on the control authority of AIC systems on the basis of theoretical considerations and measurements for an atmospheric test rig with a natural gas-fired swirl burner.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Atmospheric single-burner test rig

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Figure 2

TD2 burner design

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Figure 3

Pressure amplitudes in the secondary fuel pipe and in the combustion chamber without secondary fuel injection: open pipe (dashed) and pipe with integrated orifice (solid line)

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Figure 4

Pressure amplitudes in the secondary fuel pipe and in the combustion chamber with 5% unforced secondary fuel injection: open pipe (dashed): and pipe with integrated orifice (solid line)

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Figure 5

Pressure phases in the feed line versus the corresponding phases of the actuator: Case A with high amplitudes of secondary fuel excitation, and case B with low amplitudes of secondary fuel excitation

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Figure 6

Amplitude ratio of secondary fuel modulation in the pipe versus the corresponding phases of the actuator: Case A with high amplitudes of secondary fuel excitation and case B with low amplitudes of secondary fuel excitation

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Figure 7

Phase lags between flame response and feed-line pressure and actuator, respectively

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Figure 8

Schematic of a network model

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Figure 9

Comparison of the experimental pressure phases (filled symbols) with the calculated model results (open symbols)

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Figure 10

Comparison of the experimental pressure amplitudes (filled symbols) to the calculated model results (open symbols)

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Figure 11

Calculated phases of the secondary fuel modulation (SFM) at the injection position

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Figure 12

Calculated amplitudes of the SFM at the injection position

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Figure 13

Calculated phases of the SFM for different frequencies (normalized by the first resonance frequency) versus the corresponding phases of the actuator movement (AR=0.18)

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Figure 14

Calculated amplitudes of the SFM for different frequencies (normalized by the first resonance frequency) versus the corresponding phase of the actuator movement (AR=0.18)

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