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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

An Acoustic-Energy Method for Estimating the Onset of Acoustic Instabilities in Premixed Gas-Turbine Combustors

[+] Author and Article Information
Z. M. Ibrahim, F. A. Williams, S. G. Buckley

Center for Energy Research, Department of Mechanical and Aerospace Engineering,  University of California, San Diego, La Jolla, CA 92093

C. Z. Twardochleb

Combustion Technology,  Solar Turbines Incorporated, San Diego, CA 92108

J. Eng. Gas Turbines Power 130(5), 051506 (Jun 17, 2008) (16 pages) doi:10.1115/1.2938393 History: Received March 06, 2007; Revised March 18, 2008; Published June 17, 2008

For given acoustic frequencies of premixed gas-turbine combustors, a classical method not currently in use is explored for assessing whether acoustically driven oscillatory combustion will occur. The method involves cataloging linear amplification and attenuation mechanisms and estimating magnitudes of their rates. Linear approximations to nonlinear mechanisms are included in an effort to obtain a reasonably complete description. A stability index is defined such that oscillation is predicted to occur when the value of the index exceeds unity. The method is tested on the basis of new experiments and experimental data available in literature. Moderate success is achieved in rationalizing these experimental results. The objective of the method is to enable quick and inexpensive decisions to be made for a wide variety of potential design configurations and operating conditions, without the complexity of computational fluid dynamics. The approach therefore may complement other approaches already in use.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of a homogenous reactor

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Figure 2

Schematic of an anchored flame at a fixed location

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Figure 3

Schematic of an anchored conical flame

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Figure 4

Growth-rate results obtained from Eqs. 11,34,42 with a fixed n=0.05

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Figure 5

Growth-rate results obtained from Eqs. 39,45

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Figure 6

Growth-rate results (zoomed in near 250Hz) from effects of equivalence-ratio fluctuations, as obtained from Eq. 45

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Figure 7

Growth-rate results obtained from Eq. 45 (at a fixed pressure of 7.5atm and equivalence ratio of 0.65) for the high-pressure experiments as a function of injection velocity and frequency

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Figure 8

A schematic of the development injector used in the experiments

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Figure 9

Dynamic pressure measurements during oscillation for an annular combustor at atmospheric-pressure conditions

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Figure 10

Measured relative pressure amplitudes as functions of circumferential angle

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Figure 11

Growth-rate predictions for the atmospheric-pressure, annular combustor

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Figure 12

Dynamic pressure spectrum obtained during oscillation on a Taurus-70 engine test (full load, 4% pilot flow, and primary zone at 2853°F)

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Figure 13

Predicted growth-rate results for the annular high-pressure engine test

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Figure 14

Predicted stability results for the three performed experiments (1–500Hz)

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