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

Experimental Investigation of the Transition Mechanism From Stable Flame to Flashback in a Generic Premixed Combustion System With High-Speed Micro-Particle Image Velocimetry and Micro-PLIF Combined With Chemiluminescence Imaging

[+] Author and Article Information
Georg Baumgartner

Lehrstuhl fuer Thermodynamik,
Technische Universitaet Muenchen,
Garching D-85747, Germany
e-mail: baumgartner@td.mw.tum.de

Lorenz R. Boeck, Thomas Sattelmayer

Lehrstuhl fuer Thermodynamik,
Technische Universitaet Muenchen,
Garching D-85747, 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 13, 2015; final manuscript received July 20, 2015; published online September 1, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 021501 (Sep 01, 2015) (10 pages) Paper No: GTP-15-1271; doi: 10.1115/1.4031227 History: Received July 13, 2015

Sustainable power generation resulting in low pollutant emissions, such as CO2 and NOx, poses a very challenging task in the near future. Premixed combustion of hydrogen-rich fuels in gas turbines is a promising approach to cope with ever more stringent regulations on emission levels. This method, however, involves the risk of flame flashback from the desired flame position into the premixing section, leading to catastrophic failure of the machine components that are not designed for such high temperatures. The objective of the current study was to visualize and describe the transition from stable flame to flashback in a generic H2–air combustion system and develop a physics-based model for the description of the transition. In order to achieve the high temporal and spatial resolution required for capturing the involved effects, high-speed particle image velocimetry (PIV) and high-speed planar laser-induced fluorescence (PLIF) were employed. In order to characterize the interaction of the flame with the flow in detail, both measurement techniques were applied to very small fields-of-view using (UV) long-distance microscopes. The repetition rates were 20 kHz for PLIF and 3 kHz for PIV, respectively. During both the PLIF and the PIV measurements, the flame's OH*-chemiluminescence was captured from a perspective perpendicular to that of the PLIF/PIV camera for further flame characterization. The microscopic measurements revealed that there is a negligible influence of the unconfined flame on the incoming burner flow in stable mode. Upon approaching the flashback conditions, however, the velocity profile of the burner flow is distinctly distorted by the presence of the flame inside the premixing duct. The flow directly upstream of the flame is retarded and deflected around the leading flame tip. Based on the effects observed in the experiments, a new flashback model is proposed, which identifies the heat transfer to the burner rim and the flame speed as the main drivers for the onset of flashback, whereas the flame backpressure is the governing factor for the subsequent upstream flame propagation.

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Fig. 1

Critical gradient model (flow direction from left to right) [1,2]

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Fig. 2

Schematic of the channel burner test rig

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Fig. 3

Comparison of flashback limits of atmospheric, non-preheated hydrogen–air flames in a channel burner and in tube burners [1]*

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Fig. 4

High-speed (micro) measurement setups

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Fig. 5

Axial velocity field u (m/s) for isothermal flow (a) and stable combustion (b) (u¯  = 7 m/s, Φ  = 0.5, and T = 293 K)

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Fig. 6

Instantaneous (a) and time-averaged (b) macroscopic PLIF image of stable flame (u¯  = 7 m/s, Φ  = 0.5, and T = 293 K)

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Fig. 7

Instantaneous OH* image of flame at flashback from the top

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Fig. 8

OH* recordings of upstream flame propagation during flashback from the top; the arrow indicates the position of the leading flame tip, the dashed line indicates the downstream end of the lower burner wall, and the solid line markes the PIV laser sheet

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Fig. 9

Temporal evolution of axial velocity field u (m/s) during upstream flame propagation (μ-PIV), Δt = 0.33 ms; the black dashed line indicates the approximate shape of the leading flame part (deduced from the corresponding Mie scattering images)

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Fig. 10

Instantaneous μ-PLIF image of flame at flashback

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Fig. 12

Schematic illustration of the transition from stable flame to flashback

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Fig. 13

Schematic of the stable, unconfined flame close to the flashback limit (dimensions are not true to scale). Streamlines are shown in red and the bold dashed line illustrates the propagation path of the leading flame tip during flashback.

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Fig. 14

Terminology for burner configurations (flow direction from bottom to top)

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Fig. 15

Overview of flashback limits for atmospheric, non-preheated H2–air flames (from Ref.[36]) (a) and details of investigated tube burner configurations (b)




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