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

Formation of Soot in Ethylene–Air Partially Premixed Flames Over a Wide Range of Premixedness

[+] Author and Article Information
Aritra Chakraborty

Department of Aerospace Engineering,
National Centre for Combustion Research
and Development (NCCRD),
IIT Madras,
Chennai 600036, India
e-mail: aritra.1991@gmail.com

Satya R. Chakravarthy

Department of Aerospace Engineering,
National Centre for Combustion Research
and Development (NCCRD),
IIT Madras,
Chennai 600036, India
e-mail: src@ae.iitm.ac.in

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 June 26, 2017; final manuscript received July 5, 2017; published online September 6, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(12), 121506 (Sep 06, 2017) (6 pages) Paper No: GTP-17-1234; doi: 10.1115/1.4037580 History: Received June 26, 2017; Revised July 05, 2017

This paper reports an investigation of soot formation in ethylene–air partially premixed flames (PPFs) over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish PPFs from the fully nonpremixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in both the streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser-induced incandescence (LII) is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit an “S”-type trend as the conditions are traversed from near the premixed to the nonpremixed regimes. That is, when traversing from the nonpremixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the PPFs is clearly seen to be at the tip of the rich-premixed flame (RPF) branch of their triple flame structure, which advances upstream toward the base of the flame as the premixing is reduced. The S-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame (LPF) branch of the triple flame. LII intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

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Copyright © 2017 by ASME
Topics: Flames , Soot , Lasers , Fuels
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References

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Figures

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Fig. 1

Schematic of the burner

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Fig. 2

Schematic of laser extinction setup

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Fig. 3

Laser-induced incandescence/imaging layout

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Fig. 4

Parts of a triple flame indicating LPF, RPF, and DF branches of the triple flame

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Fig. 5

Flame images through varied premixedness

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Fig. 6

Nascent sooting flame images

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Fig. 7

Soot volume fraction versus percentage inner fuel

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Fig. 8

Time-averaged LII signals

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Fig. 9

Comparison of LII-integrated fv (left ordinate) with the laser extinction based fv (right ordinate) from Fig. 7

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Fig. 10

Soot base location from burner lip (from flame luminosity)

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Fig. 11

Shift in sooting base (from LII contours)

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Fig. 12

Red matrix of flame image with 650 nm BP filter

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Fig. 13

Soot isolated images obtained by subtracting the BG-3 filtered images from the 650 nm BP filtered red matrix images

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Fig. 14

Normalized sum of intensities of the soot isolated images compared to laser extinction based estimation

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