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

Flame Holding in the Premixing Zone of a Gas Turbine Model Combustor After Forced Ignition of H2–Natural Gas–Air Mixtures

[+] Author and Article Information
Matthias Utschick

Lehrstuhl für Thermodynamik,
Technische Universität München,
Garching 85748, Germany
e-mail: utschick@td.mw.tum.de

Thomas Sattelmayer

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

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 1, 2016; final manuscript received August 2, 2016; published online October 26, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 041504 (Oct 26, 2016) (10 pages) Paper No: GTP-16-1300; doi: 10.1115/1.4034647 History: Received July 01, 2016; Revised August 02, 2016

Flashback (FB) and self-ignition in the premixing zone of typical gas turbine swirl combustors in lean premixed operation are immanent risks and can lead to damage and failure of components. Thus, steady combustion in the premixing zone must be avoided under all circumstances. This study experimentally investigates the flame holding propensity of fuel injectors in the swirler of a gas turbine model combustor with premixing of H2–natural gas (NG)–air mixtures under atmospheric pressure and proposes a model to predict the limit for safe operation. The A2EV swirler concept exhibits a hollow, thick walled conical structure with four tangential slots. Four fuel injector geometries were tested. One of them injects the fuel orthogonal to the air flow in the slots (jet-in-crossflow injector, JICI). Three injector types introduce the fuel almost isokinetic to the air flow at the trailing edge of the swirler slots (trailing edge injector, TEI). A cylindrical duct and a window in the swirler made of quartz glass allow the application of optical diagnostics (OH* chemiluminescence and planar laser induced fluorescence of the OH radical (OH-PLIF)) inside the swirler. The fuel–air mixture was ignited with a focused single laser pulse during steady operation. The position of ignition was located inside the swirler in proximity to a fuel injection hole. If the flame was washed out of the premixing zone not later than 4 s after the ignition, the operation point was defined as safe. Operation points were investigated at three air mass flows, three air ratios, two air preheat temperatures (573 K and 673 K), and 40 to 100 percent per volume hydrogen in the fuel composed of hydrogen and natural gas. The determined safety limit for atmospheric pressure yields a similarity rule based on a critical Damköhler number. Application of the proposed rule at conditions typical for gas turbines leads to these safety limits for the A2EV burner: With the TEIs, the swirler can safely operate with up to 80 percent per volume hydrogen content in the fuel at an air ratio of two. With the JIC injector, safe operation at stoichiometric conditions and 95 percent per volume hydrogen is possible.

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Figures

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Fig. 1

Inclined JIC after Ref. [4]

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Fig. 2

A2EV combustor concept

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Fig. 3

A2EV swirler and gas injectors

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Fig. 4

Reference system in the swirler

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Fig. 5

Flow conditions and imaging in the swirler

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Fig. 6

Laser ignition in the swirler

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Fig. 7

Mean jet flame position in LS1 and LS2 after a FB; 500 instantaneous OH-PLIF recordings have been used for the mean image

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Fig. 8

OH* flame radiation recordings after forced ignition in ZP1 with Inj. A at m˙a= 100 g/s, λ = 3, and XH2,f=0.80 (safe operation point)

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Fig. 9

OH-PLIF recordings after forced ignition in ZP1 with Inj. A at m˙a= 100 g/s, λ = 3, and XH2,f=0.80 (safe operation point)

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Fig. 10

Operating conditions determining the safety limit

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Fig. 11

Correlating the operational safety with a critical Damköhler number; below the black line is the safe range. Left: current experiment and right: computed values for r and Da at varied temperature or pressure with Inj. A and D corresponding to λ=2.5 and m˙a,0=80 g/s.

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Fig. 12

Uncertainty of the Daˇ model predictions

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Fig. 13

Dˇa model applied to literature data

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Fig. 14

Safety maps for Inj. A–D (Ta=400 °C and Tf=283 °C); isolines and color represent the air speed in the swirler slots

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Fig. 15

Safety maps for Inj. A and D computed at p = 20 bar (Ta=400 °C and Tf=283 °C)

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