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

Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures

[+] Author and Article Information
Christian Eichler1

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, 85748 Garching, Germanyeichler@td.mw.tum.de

Thomas Sattelmayer

Lehrstuhl für Thermodynamik, Technische Universität München, Boltzmannstraße 15, 85748 Garching, Germany

NG with a mean CH4 content of 97.63 vol % was used as a substitute.

1

Corresponding author.

J. Eng. Gas Turbines Power 133(1), 011503 (Sep 14, 2010) (7 pages) doi:10.1115/1.4001985 History: Received April 08, 2010; Revised April 21, 2010; Published September 14, 2010; Online September 14, 2010

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups were investigated in the past, and thus turbulent flashback limits were only derived for a fully developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen, and air at various mixing ratios. The associated wall friction distributions are determined by Reynolds-averaged Navier-Stokes (RANS) computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared with literature values, and the critical gradient concept is reviewed in light of the new data.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

2D model of flow and flame configuration at the onset of laminar BLF

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Figure 2

Literature results for BLF in tube burners during atmospheric premixed H2-air combustion

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Figure 3

Overview of measurement section and combustion chamber

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Figure 4

Details of the measurement section

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Figure 5

Mean velocity profiles at combustion chamber inlet (ṁ=50 g/s, pure air). (a) Velocity profiles across full channel height and width. (b) Wall-near velocities at the center of the lower wall.

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Figure 6

Instantaneous H2-air flame shape and position at BLF (ṁair=100 g/s, Φ=0.29)

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Figure 7

Numerical results for wall shear stress along the lower diffuser wall

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Figure 8

Time averaged flame images for the determination of mean flame tip position at turbulent BLF. (a) CH4, ṁair=40 g/s, and Φ=0.8. (b) CH4, ṁair=50 g/s, and Φ=0.8. (c) H2, ṁair=50 g/s, and Φ=0.25. (d) H2, ṁair=60 g/s, and Φ=0.25. (e) H2, ṁair=100 g/s, and Φ=0.29. (f) H2, ṁair=120 g/s, and Φ=0.29.

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