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

Optical Transfer Function Measurements for Technically Premixed Flames

[+] Author and Article Information
Bruno Schuermans, Felix Guethe, Wolfgang Mohr

 Alstom, Baden CH-5405, Switzerland

J. Eng. Gas Turbines Power 132(8), 081501 (May 06, 2010) (8 pages) doi:10.1115/1.3124663 History: Received April 01, 2008; Revised April 11, 2008; Published May 06, 2010; Online May 06, 2010

This paper deals with a novel approach for measuring thermoacoustic transfer functions. These transfer functions are essential to predict the acoustic behavior of gas turbine combustion systems. Thermoacoustic prediction has become an essential step in the development process of low NOx combustion systems. The proposed method is particularly useful in harsh environments. It makes use of simultaneous measurement of the chemiluminescence of different species in order to obtain the heat release fluctuations via inverse method. Generally, the heat release fluctuation has two contributions: one due to equivalence ratio fluctuations, and the other due to modulations of mass flow of mixture entering the reaction zone. Because the chemiluminescence of one single species depends differently on the two contributions, it is not possible to quantitatively estimate the heat based on this information. Measurement of the transfer matrix based on a purely acoustic method provides quantitative results, independent of the nature of the interaction mechanism. However, this method is difficult to apply in industrial full-scale experiments. The method developed in this work uses the chemiluminescence time traces of several species. After calibration, an overdetermined inverse method is used to calculate the two heat release contributions from the time traces. The optical method proposed here has the advantage that it does not only provide quantitative heat release fluctuations but it also quantifies the underlying physical mechanisms that cause the heat release fluctuations: It shows what part of the heat release is caused by equivalence ratio fluctuations and what part by flame front dynamics. The method was tested on a full scale swirl-stabilized gas turbine burner. Comparison with a purely acoustic method validated the concept.

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Figures

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Figure 1

Experimental setup: atmospheric pressure combustion test equipped facility with loudspeakers, microphones, and optical access via a fiber bundle

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Figure 2

Transmission curve of the filters used and flame spectrum from a test flame

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Figure 3

Normalized mean chemiluminescence intensity as a function of adiabatic flame temperature and mixture mass flow. Crosses: measured data; circles: data fit using Eq. 2; solid line: trend line of Eq. 2

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Figure 4

Comparison of heat release obtained from acoustic data (dashed) with heat release obtained from optical data according to Eqs. 11,3 (solid) and the relative OH∗ intensity fluctuations (dash-dotted)

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Figure 5

Comparison of transfer matrix elements F12 and F22 obtained from acoustic data (dotted) using equation Eqs. 19,23 and obtained from optical data (solid) using Eqs. 11,14,16

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Figure 6

Absolute values (solid) and phase (dashed) of the matrix elements of C

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