Spatial Variation Of Soot Volume Fractions In Pool Fire Diffusion Flames

Flame radiation, the dominant heat transfer mechanism in many combustion and fire safety related problems, is primarily controlled by the fraction of flame volume occupied by solid carbon particulate. A multi-wavelength laser transmission technique is used here to measure carbon particulate volume fractions and approximate particle size distributions in ten common solid, cellular and liquid fueled small scale, 0 (10 cm dia), pool fire diffusion flames. The most probable particle radius, rmax, and concentration, N0, are two parameters in the assumed gamma function size distribution form which are determined for each fuel by simultaneously measuring light transmission of two superimposed laser wavelengths. The resulting soot volume fractions range from fv ∼ 4 × 10−6 for cellular polystyrene to fv ∼ 7 × 10−8 for alcohol. Cellular polystyrene has the largest particles, rmax ∼ 60 nm while wood has the smallest, rmax ∼ 20 nm. The carbon particulate optical properties used in the analysis are shown to be representative of actual flame soot and are more accurate than the soot refractive index usually assumed in the literature. Finally, mean particle sizes obtained for all fuels indicate that the small particle absorption limit assumption is a reasonable approximation for infrared flame radiation calculations.

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Particulate volume fractions in diffusion flames

Symposium (International) on Combustion ◽

10.1016/s0082-0784(79)80098-3 ◽

1979 ◽

Vol 17 (1) ◽

pp. 1017-1028 ◽

Cited By ~ 10

Author(s):

P.J. Pagni ◽

S. Bard

Keyword(s):

Diffusion Flames ◽

Volume Fractions ◽

Particulate Volume

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Soot Volume Fraction Profiles in Forced-Combusting Boundary Layers

Journal of Heat Transfer ◽

10.1115/1.3245535 ◽

1983 ◽

Vol 105 (1) ◽

pp. 159-165 ◽

Cited By ~ 9

Author(s):

R. A. Beier ◽

P. J. Pagni

Keyword(s):

Boundary Layer ◽

Mass Fraction ◽

Volume Fraction ◽

Diffusion Flames ◽

Soot Volume Fraction ◽

Liquid Hydrocarbon ◽

Forced Flow ◽

Volume Fractions ◽

Ambient Oxygen ◽

Mass Fractions

A multiwavelength laser transmission technique is used to determine soot volume fraction fields and aproximate particle size distributions in a forced flow combusting boundary layer. Measurements are made in diffusion flames of polymethylmethacrylate (PMMA) and five liquid hydrocarbon fuels (n-heptane, iso-octane, cyclohexane, cyclohexene, and toluene) with ambient oxygen mass fractions in the range of 0.23 ≲ Y0∞ ≲ 0.50. Soot is observed in a region between the pyrolyzing fuel surface and the flame zone. Soot volume fraction increases monotonically with Y0∞, e.g., n-heptane and PMMA are similar with soot volume fractions, fν, ranging from fν ∼ 5 × 10−7 at Y0∞ = 0.23 to fν ∼ 5 × 10−6 at Y0∞ = 0.50. For an oxygen mass fraction the same as air, Y0∞ = 0.23, soot volume fractions are approximately the same as values previously reported in pool fires and a free combusting boundary layer. However, the shape of the fν profile changes with more soot near the flame in forced flow than in free flow due to the different y-velocity fields in these two systems. For all fuels tested, a most probable particle radius is between 20 nm and 80 nm, and does not appear to change substantially with location, fuel, or oxygen mass fraction.

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