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

Transient Development of Flame and Soot Distribution in Laminar Diffusion Flame With Preheated Air

[+] Author and Article Information
Bijan Kumar Mandal

Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, Howrah, 711109, India

Amitava Sarkar

Department of Mechanical Engineering, Jadavpur University, Kolkata 700032, India

Amitava Datta

Department of Power Engineering, Jadavpur University, Salt Lake Campus, Kolkata 700098, India

J. Eng. Gas Turbines Power 131(3), 031501 (Jan 29, 2009) (9 pages) doi:10.1115/1.3018978 History: Received September 21, 2007; Revised August 27, 2008; Published January 29, 2009

A numerical investigation of the transient development of flame and soot distributions in a laminar axisymmetric coflowing diffusion flame of methane in air has been carried out considering the air preheating effect. The gas phase conservation equations of mass, momentum, energy, and species concentrations along with the conservation equations of soot mass concentration and number density are solved simultaneously, with appropriate boundary conditions, by an explicit finite difference method. Average soot diameters are then calculated from these results. It is observed that the soot is formed in the flame when the temperature exceeds 1300 K. The contribution of surface growth toward soot formation is more significant compared with that of nucleation. Once the soot particles reach the high temperature oxygen-enriched zone beyond the flame, the soot oxidation becomes important. During the initial period, when soot oxidation is not contributing significantly, some of the soot particles escape into the atmosphere. However, under steady condition the exhaust product gas is nonsooty. Preheating of air increases the soot volume fraction significantly. This is both due to more number of soot particles and the increase in the average diameter. However, preheating of air does not cause a qualitative difference in the development of the soot-laden zone during the flame transient period.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 5

Variation of (a) total soot volume and (b) cumulative soot particle number in the computational domain with time after ignition with normal air

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Figure 6

Flame front surface (dotted thick line) and soot diameter contours at different times after ignition with nonpreheated air: (a) t=0.05 s, (b) t=0.10 s, (c) t=0.15 s, (d) t=0.20 s, (e) t=0.40 s, and (f) t=0.80 s

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Figure 7

Flame front surface (thick dashed line) along with temperature (K) and velocity distributions for the steady diffusion flame with preheated air

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Figure 8

(a) Centerline temperature and (b) centerline velocity distribution for the diffusion flame with and without air-preheat

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Figure 1

Comparison of the radial distributions of (a) temperature and (b) CO2 and H2O predicted by the present model against the experimental data of Mitchell (17) at 12 mm above the burner

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Figure 2

Radial distribution of the soot volume fraction in diffusion flame at nondimensional axial heights (a) z/HF=0.5, and (b) z/HF=0.69; comparison of the present prediction (solid line) against Smooke (3)

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Figure 3

Flame front surface (thick dashed line) along with temperature (K) and velocity distributions for the steady diffusion flame with nonpreheated air

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Figure 4

Flame front surface (thick dotted line) and soot volume fraction contours at different times after ignition with nonpreheated air: (a) t=0.05 s, (b) t=0.10 s, (c) t=0.15 s, (d) t=0.20 s, (e) t=0.4 s, and (f) t=0.8 s

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Figure 9

Flame front surface (dashed thick line) and (a) soot volume fraction contours; and (b) soot diameter contours with preheated air under steady state

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Figure 10

Flame front surface (thick dotted line) and soot volume fraction contours at various times after ignition with preheated air: (a) t=0.10 s, (b) t=0.20 s, (c) t=0.40 s, and (d) t=1.60 s

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