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

Visualization of Different Flashback Mechanisms for H2/CH4 Mixtures in a Variable-Swirl Burner

[+] Author and Article Information
Parisa Sayad

Mem. ASME
Department of Energy Sciences,
Ole Römers Vägen1,
Lund 22100, Sweden
e-mail: parisa.sayad@energy.lth.se

Alessandro Schönborn

Department of Energy Sciences,
Ole Römers Vägen1,
Lund 22100, Sweden
e-mail: alessandro.schonborn@energy.lth.se

Mao Li

Department of Energy Sciences,
Ole Römers Vägen1,
Lund 22100, Sweden
e-mail: mao.li@energy.lth.se

Jens Klingmann

Professor
Department of Energy Sciences,
Ole Römers Vägen1,
Lund 22100, Sweden
e-mail: Jens.klingmann@energy.lth.se

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 24, 2014; final manuscript received July 29, 2014; published online October 7, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(3), 031507 (Oct 07, 2014) (9 pages) Paper No: GTP-14-1432; doi: 10.1115/1.4028436 History: Received July 24, 2014; Revised July 29, 2014

Flame flashback from the combustion chamber to the premixing section is a major operability issue when using high H2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, flashback can be triggered by different mechanisms. In this work, three flashback mechanisms of H2/CH4 mixtures were visualized in an atmospheric variable-swirl burner using high speed OH* chemiluminescence imaging. The H2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown (CIVB) occurred at swirl numbers 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer (BL) and flame propagation in the premixing tube caused by auto-ignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during flashback was studied and flashback speed for different mechanisms was estimated. The flame propagation speed during flashback was significantly different for the different mechanisms.

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References

Figures

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Fig. 1

Variable-swirl burner with optical access

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Fig. 2

Cross section of swirler, premixing tube, and combustor

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Fig. 3

Swirl number as a function of ratio of axial/tangential momentum

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Fig. 4

Normalized axial velocity profiles obtained from LDA measurements for different swirl numbers

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Fig. 5

Normalized tangential velocity profiles obtained from LDA measurements for different swirl numbers

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Fig. 6

Different flashback mechanisms observed under various test conditions

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Fig. 7

OH* chemiluminescence image sequence of upstream flame propagation caused by CIVB. Image interval = 0.444 ms, exposure time = 72 μs, swirl number = 0.66, fuel H2 mole fraction = 0.9, Φ = ΦFB = 0.234.

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Fig. 8

OH* chemiluminescence image sequence of upstream flame propagation in the boundary layer. Image interval = 2.072 ms, exposure time = 72 μs, swirl number = 0.0, fuel H2 mole fraction = 0.9, Φ = ΦFB = 0.671.

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Fig. 9

OH* chemiluminescence image sequence of flame propagation in the premixing tube caused by auto-ignition. Image interval = 0.074 ms, exposure time = 72 μs, swirl number = 0.24, fuel H2 mole fraction = 0.15, Φ = ΦFB = 0.696.

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Fig. 10

OH* chemiluminescence image sequence of blowout of the flame due to auto-ignition. Image interval = 0.074 ms, exposure time = 72 μs, swirl number = 0.24, fuel H2 mole fraction = 0.15, Φ = ΦFB = 0.696.

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Fig. 11

Adiabatic flame temperature at flashback as a function of H2 mole fraction

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Fig. 12

Flame front displacement in the optical section of the premixing tube during the flashback events for various fuel H2 mole fraction/flashback mechanisms

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Fig. 13

Linear approximation of the flame front displacement for various fuel H2 mole fraction/flashback mechanisms

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Fig. 14

The displacement of the second flame front in the premixing tube obtained in four flashback events caused by auto-ignition under the same condition: swirl number = 0.24, fuel H2 mole fraction = 0.15, Φ = ΦFB = 0.696

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Fig. 15

Equivalence ratio at flashback as a function of total air mass-flow rate (the H2 mole fraction of the mixtures are presented next to each data point)

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