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

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames

[+] Author and Article Information
Thomas Sattelmayer

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

Christoph Mayer, Janine Sangl

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 June 29, 2015; final manuscript received July 1, 2015; published online August 25, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(1), 011503 (Aug 25, 2015) (12 pages) Paper No: GTP-15-1224; doi: 10.1115/1.4031239 History: Received June 29, 2015; Revised July 01, 2015

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

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Figures

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Fig. 1

Burner geometry and fuel injection concept

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Fig. 2

Scheme of the atmospheric test rig

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Fig. 3

Processing of HS-PIV and OH*-chemiluminescence results (mixing tube)

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Fig. 4

OH*-chemiluminescence (bottom, line-of-sight integrated), axial flow velocities (top, planar), and flame front (planar) during flashback for the configuration without diffuser (ub = 25 m/s)

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Fig. 5

Radial profiles of the axial velocity at different axial locations without flame (ub = 21.6 m/s)

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Fig. 6

Comparison of flashback data with engine conditions and laminar flame velocity

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Fig. 12

Average OH*-chemiluminescence for different TE injection configurations (top: line-of-sight, bottom: inverse Abel transformed [23])

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Fig. 11

Schematic for the selection of the appropriate swirler aerodynamics

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Fig. 14

OH*-chemiluminescence and ionization sensor signals during flashback

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Fig. 10

Flame propagation velocities in axial Su and azimuthal Sw direction (ub = 35.4 m/s)

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Fig. 9

OH*-chemiluminescence during flashback [8]

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Fig. 8

OH*-chemiluminescence and axial velocity field during the transition of flame stabilization

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Fig. 7

Instantaneous Mie-scattering image, average axial flow velocities and average inverse Abel transformed OH*-chemiluminescence images (ub = 24 m/s)

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Fig. 13

Secondary air injection with one (left) and two (right) injection slots

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Fig. 15

Axial velocity profiles before and after the transition of the flame stabilization pattern compared with the laminar flame speed

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