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

Soot Formation and Flame Characterization of an Aero-Engine Model Combustor Burning Ethylene at Elevated Pressure

[+] Author and Article Information
Klaus Peter Geigle

German Aerospace Center (DLR),
Institute of Combustion Technology,
Stuttgart 70569, Germany
e-mail: klauspeter.geigle@dlr.de

Redjem Hadef

Université Larbi Ben M'Hidi
Institut de Génie Mécanique,
Oum El Bouaghi 04200, Algerie

Wolfgang Meier

German Aerospace Center (DLR),
Institute of Combustion Technology,
Stuttgart 70569, Germany

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 11, 2013; final manuscript received August 14, 2013; published online October 28, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(2), 021505 (Oct 28, 2013) (7 pages) Paper No: GTP-13-1302; doi: 10.1115/1.4025374 History: Received August 11, 2013; Revised August 14, 2013

Swirl-stabilized, nonpremixed ethylene/air flames were investigated at pressures up to 5 bar to study the effect of different operating parameters on soot formation and oxidation. Focus of the experiments was the establishment of a database describing well-defined flames, serving for validation of numerical simulation. Good optical access via pressure chamber windows and combustion chamber windows enables application of laser-induced incandescence to derive soot volume fractions after suitable calibration. This results in ensemble averaged, as well as instantaneous soot distributions. Beyond pressure, parameters under study were the equivalence ratio, thermal power, and amount of oxidation air. The latter could be injected radially into the combustor downstream of the main reaction zone through holes in the combustion chamber posts. Combustion air was introduced through a dual swirl injector whose two flow rates were controlled separately. The split of those air flows provided an additional parameter variation. Nominal power of the operating points was approximately 10 kW/bar leading to a maximum power of roughly 50 kW, not including oxidation air.

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Figures

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Fig. 1

Design of burner, combustion chamber, and optical module of pressure housing

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Fig. 2

Laser sheet characteristics as determined with a beam profiler (left, center). The right plot shows the LII response curve measured in a stable laminar diffusion flames (evaluation rectangle is labeled in flame image) and the chosen pulse energy of 32 mJ.

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Fig. 3

Different information available for one exemplary flame at p = 3 bar, ϕ = 1.2, P = 30 kW, Qair,c/Qair = 0.3, Qoxi/Qair = 0.4 (reference case). From left to right: photo (exposure 500 μs), time averaged image of soot luminosity (integrated along line of sight, also available as instantaneous images), single shot of LII signal for one sheet position, averaged LII image (400 laser pulses) and time-averaged, deconvoluted OH chemiluminescence. All LII images are 60.4 mm × 113.8 mm large, the OH image measures 55.7 mm × 93.3 mm.

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Fig. 4

Influence of a variation of oxidation air Qoxi/Qair for operation at p = 3 bar, ϕ = 1.2, P = 30 kW, Qair,c/Qair = 0.3 on the soot distribution (in ppb); the amount of oxidation air is indicated above the images

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Fig. 5

Influence of a variation of flame power P for operation at p = 3 bar, ϕ = 1.2, Qair,c/Qair = 0.3, Qoxi/Qair = 0.4 on the soot distribution (in ppb). This corresponds to an increase of the respective Reynolds number by one third. The flame power is indicated above the images.

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Fig. 6

Variation of air split Qair,c/Qair for operation at p = 3 bar, ϕ = 1.2, P = 30 kW, Qoxi/Qair = 0.4 (left and central image, values of air split are listed in the top row above the images). Variation of pressure p for flames at ϕ = 1.2, P = 30 kW, Qair,c/Qair = 0.3, Qoxi/Qair = 0.4 is compared between central and right image, both showing different soot concentration scales.

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Fig. 7

Variation of equivalence ratio ϕ for operation at p = 5 bar, P = 50 kW, Qair,c/Qair = 0.3, Qoxi/Qair = 0.4

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Fig. 8

Instantaneous soot volume fraction images (ppm) composed of arbitrarily selected images for each laser sheet position for the 1 bar ignition flame (left), the reference flame (center), and the respective flame without oxidation air (time averages of the latter two are presented in Fig. 4)

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Fig. 9

Probability within image sequences of finding soot in a single location. The central image represents the reference flame, variation to the left is without oxidation air (zero), to the right is pressure (5 bar). The bottom rows display statistics over the number of soot filaments per instantaneous image, plotted for the second laser sheet position (second row), and the lowest position (bottom).

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Fig. 10

Instantaneous image statistics for reference flame at 3 bar (left) and pressure variation (5 bar, right). Upper images show three representative and one particularly strong single shot image, histograms visualize probabilities for peak.

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