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

Impact of Cooling Air Injection on the Primary Combustion Zone of a Swirl Burner

[+] Author and Article Information
A. Marosky

e-mail: marosky@td.mw.tum.de

T. Sattelmayer

Lehrstuhl für Thermodynamik,
Technische Universität München,
85748 Garching, Germany

F. Magni

Alstom Ltd.,
5401 Baden, Switzerland

1Address all correspondence to this author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 19, 2012; final manuscript received June 27, 2012; published online October 11, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 134(12), 121502 (Oct 11, 2012) (8 pages) doi:10.1115/1.4007330 History: Received June 19, 2012; Revised June 27, 2012

In most dry, low NOx combustor designs, the front panel impingement cooling air is directly injected into the combustor primary zone. As this air partially mixes with the swirling flow of premixed reactants from the burner prior to completion of heat release, it reduces the effective equivalence ratio in the flame and has a beneficial effect on NOx emissions. However, the fluctuations of the equivalence ratio in the flame potentially increase heat release fluctuations and influence flame stability. Since both effects are not yet fully understood, isothermal experiments are made in a water channel, where high speed planar laser-induced fluorescence (HSPLIF) is applied to study the cooling air distribution and its fluctuations in the primary zone. In addition, the flow field is measured with high speed particle image velocimetry (HSPIV). Both mixing and flow field are also analyzed in numerical studies using isothermal large eddy simulation (LES), and the simulation results are compared with the experimental data. Of particular interest is the influence of the injection configuration and cooling air momentum variation on the cooling air penetration and dispersion. The spatial and temporal quality of mixing is quantified with probability density functions (PDF). Based on the results regarding the equivalence ratio fluctuations, regions with potential negative effects on combustion stability are identified. The strongest fluctuations are observed in the outer shear layer of the swirling flow, which exerts a strong suction effect on the cooling air. Interestingly, the cooling air dilutes the recirculation zone of the swirling flow. In the reacting case, this effect is expected to lead to a decrease of the temperature in the flame-anchoring zone below the adiabatic flame temperature of the premixed reactant, which may have an adverse effect on flame stability.

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References

Figures

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Fig. 1

Modular design of the front plate (left) and dimensions of the three configurations of cooling air injection (right)—small annular gap (SAG), large annular gap (LAG), injection rows (INJ)

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Fig. 2

Principle of the HSPLIF setup of water test rig

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Fig. 3

Camera calibration curve

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Fig. 4

Signal decay in raw data of uniform concentration distribution

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Fig. 5

Scheme of absorption correction

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Fig. 6

Fluctuation of laser intensity

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Fig. 7

Mean axial flow field (HSPIV): without injection (WO); detail of cooling air injection through injector rows (INJ); small annular gap (SAG); large annular gap (LAG)

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Fig. 8

Mean (top) and RMS (bottom) of mixture fraction (HSPLIF): injector rows (INJ); small annular gap (SAG); large annular gap (LAG)

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Fig. 9

Mean mixture fraction by HSPLIF and LES for INJ, SAG, and LAG

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Fig. 10

Data points for evaluation of mixture fraction PDF

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Fig. 11

Mixture fraction PDF along burner center axis for LAG, SAG, INJ with constant injection momentum

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Fig. 12

Scaled mixture fraction PDF along burner center axis for varying momentum (LAG)

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Fig. 13

Scaled mixture fraction PDF field for varying injection momentum (LAG)

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