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

Impact of Cooling Air Injection on the Combustion Stability of a Premixed Swirl Burner Near Lean Blowout

[+] Author and Article Information
A. Marosky

e-mail: marosky@td.mw.tum.de

T. Sattelmayer

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

W. Geng

Alstom Power,
Baden 5401, Switzerland

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 17, 2013; final manuscript received July 17, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 111501 (Sep 17, 2013) (9 pages) Paper No: GTP-13-1168; doi: 10.1115/1.4025043 History: Received June 17, 2013; Revised July 17, 2013

In most dry, low-NOx combustor designs of stationary gas turbines, the front panel impingement cooling air is directly injected into the combustor primary zone. This air partially mixes with the swirling flow of premixed reactants from the burner and reduces the effective equivalence ratio in the flame. However, local unmixedness and the lean equivalence ratio are supposed to have a major impact on combustion performance. The overall goal of this investigation is to answer the question of whether the cooling air injection into the primary combustor zone has a beneficial effect on combustion stability and NOx emissions or not. The flame stabilization of a typical swirl burner with and without front panel cooling air injection is studied in detail under atmospheric conditions close to the lean blowout limit (LBO) in a full-scale, single-burner combustion test rig. Based on previous isothermal investigations, a typical injection configuration is implemented for the combustion tests. Isothermal results of experimental studies in a water test rig adopting high-speed planar laser-induced fluorescence (HSPLIF) reveal the spatial and temporal mixing characteristics for the experimental setup studied under atmospheric combustion. This paper focuses on the effects of cooling air injection on both flame dynamics and emissions in the reacting case. To reveal dependencies of cooling air injection on combustion stability and NOx emissions, the amount of injected cooling air is varied. OH*-chemiluminescence measurements are applied to characterize the impact of cooling air injection on the flame front. Emissions are collected for different cooling air concentrations, both global measurements at the chamber exit, and local measurements in the region of the flame front close to the burner exit. The effect of cooling air injection on pulsation level is investigated by evaluating the dynamic pressure in the combustor. The flame stabilization at the burner exit changes with an increasing degree of dilution with cooling air. Depending on the amount of cooling, only a specific share of the additional air participates in the combustion process.

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Fig. 1

Cross section of front panel cooling setup (left) and dimensions of the cooling air injection (right)

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Fig. 2

Schematic setup of combustion tests

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Fig. 3

Mean (left) and rms (right) of mean mixture fraction (HSPLIF), 10% cooling air, water channel

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Fig. 4

Mean mixture fraction (HSPLIF) for varying amounts of cooling air, 3%–10%, water channel

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Fig. 5

Mixing path of cooling air injection, 10% cooling air, water channel

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Fig. 6

Mean (left) and rms (right) of OH*-chemiluminescence (Abel-deconvoluted) close to LBO for varying amount of cooling air

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Fig. 7

Mean (left) and rms (right) of OH*-chemiluminescence (Abel-deconvoluted) close to LBO at r/D = 0.3 dependent on cooling air and equivalence ratio

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Fig. 8

OH*-chemiluminescence (line of sight): Characteristic time sequence (Δt = 16 ms) for 3.0% and 10.7% cooling air close to LBO (ϕp = 0.435, 0.500)

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Fig. 9

Global NOx emissions close to LBO for varying amount of cooling air

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Fig. 10

Field of local emissions NOx, CO, and O2 for cooling air 3.0%, 10.7% at ϕp = 0.435, 0.500

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Fig. 11

Determination of amount of cooling air not participating in combustion (based on dependency of global NOx on equivalence ratio ϕp)

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Fig. 12

Cooling air not participating in combustion for ϕp = 0.455, 0.475, 0.500 and varying cooling air

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Fig. 13

Pulsation spectra at ϕp = 0.500 and ϕp = 0.435 for selected cooling air concentrations

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Fig. 14

Peak pulsation level of all cooling air concentrations at studied equivalence ratios




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