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

Predicting Flashback Limits of a Gas Turbine Model Combustor Based on Velocity and Fuel Concentration for H2–Air Mixtures

[+] Author and Article Information
Matthias Utschick

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

Daniel Eiringhaus, Christian Köhler, 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 18, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(4), 041502 (Oct 18, 2016) (10 pages) Paper No: GTP-16-1299; doi: 10.1115/1.4034646 History: Received July 01, 2016; Revised August 02, 2016

This study investigates the influence of the fuel injection strategy on safety against flashback in a gas turbine model combustor with premixing of H2–air mixtures. The flashback propensity is quantified and the flashback mechanism is identified experimentally. 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)). Velocity and mixing fields in mixing zone and combustion chamber in isothermal water flow were measured with high-speed particle image velocimetry (PIV) and high-speed laser-induced fluorescence (LIF). The flashback limit was determined under atmospheric pressure for three air mass flows and 673 K preheat temperature for H2–air mixtures. Flashback mechanism and trajectory of the flame tip during flashback were identified with two stereoscopically oriented intensified high-speed cameras observing the OH* radiation. We notice flashback in the core flow due to combustion-induced vortex breakdown (CIVB) and turbulent flame propagation (TFP) near the wall dependent on the injector type. The flashback resistance (FBR) defined as the ratio between a characteristic flow speed and a characteristic flame speed measures the direction of propagation of a turbulent flame in the flow field. Although CIVB cannot be predicted solely based on the FBR, its distribution gives evidence for CIVB-prone states. The fuel should be injected preferably isokinetic to the air flow along the entire trailing edge in order to reduce the RMS fluctuation of velocity and fuel concentration. The characteristic velocity in the entire cross section of the combustion chamber inlet should be at least twice the characteristic flame speed. The position of the stagnation point should be tuned to be located in the combustion chamber by adjusting the axial momentum. Those measures lead to safe operation with highly reactive fuels at high equivalence ratios.

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Figures

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Fig. 1

A2EV combustor concept

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Fig. 2

A2EV swirler and gas injectors

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Fig. 3

Stereoscopic camera setup for FB path recordings in the mixing tube

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Fig. 4

Normalized mean axial velocity u¯z/ub as well as OH* radiation for m˙a=100 g/s and varied fuel mass flow m˙f and injector type

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Fig. 5

Normalized mean axial velocity along the burner axis (left side) and normalized mean tangential velocity in LS2 (right) for m˙a=100 g/s at λ = 2 and λFB

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Fig. 6

Characteristic velocity (u¯z−u′z,RMS)/ub and OH* radiation for m˙a=100 g/s and varied fuel mass flow m˙f and injector type

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Fig. 7

Normalized hydrogen mole fraction Xf/Xf,0 and OH* radiation for m˙a=100 g/s and varied fuel mass flow m˙f and injector type

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Fig. 8

FB limit at atmospheric pressure

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Fig. 9

Flashback trajectories in z–x plane at three air mass flows m˙a=60, 80, and 100 g/s

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Fig. 10

Flashback event with Inj. A

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Fig. 11

Stereoscopic OH* recordings with Inj. A corresponding to Fig. 10

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Fig. 12

Flashback event with Inj. D

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Fig. 13

Stereoscopic OH* recordings with Inj. D corresponding to Fig. 12

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Fig. 14

Characteristic velocity ratio ξl,Δpf and OH* radiation for m˙a=100 g/s and varied fuel mass flow m˙f and injector type

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Fig. 15

Flame–flow field interaction for swirl stabilized flame

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