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Soot Formation in the Buoyancy-Dominated Ethane Diffusion Flame.

pdf icon Soot Formation in the Buoyancy-Dominated Ethane Diffusion Flame. (1095 K)
Subramaniasivam, H.

NIST GCR 92-609; 46 p. July 1992.


National Institute of Standards and Technology, Gaithersburg, MD
Order number: PB92-213396


soot; soot formation; diffusion flames; fuel flow rate; air flow; sampling; ethylene; predictive models; laminar flames; lasers; particle size


A sampling technique, based on the phenomenon of thermophoresis is used here, in order to study the soot morphology within a buoyancy-dominated ethene diffusion flame. The buoyancy-dominated flame has a fuel flow rate of 50 cc/s and a co-annular air flow of 107 cc/s. Soot morphologies at each sampling location are obtained on carbon-coated grids through a fast probe drive mechanism, and they are analyzed under a transmission electron microscope. These observations, coupled with temperature measurements at various heights of the buoyancy-dominated flame, leads to a basic understanding of particle inception region, surface growth, aggregate formation, oxidation process, aggregate size and primary particle size within this flame. Change in soot morphology is studied both in the vertical and radial axes of this flame. The intense particle inception region, characterized by a large concentration of liquid-like microdroplets, is contained within the low part of the flame. These microdroplets form on the fuel side of the flame front where the temperature is the highest. Above the inception region aggregates of increasing size are observed, i.e., increasing number of primary particles, while the primary particles themselves undergo surface growth. Surface growth in primary particles ceases to exist above the vortex region of the flame, i.e., above Z=15 cm. Since there is very little evidence of oxidation taking palce within this buoyancy-dominated flame, it is concluded that most of the soot formed in this flame is released into the surroundings. Observations being made here have been comapred to similar soot morphology studies previously made on laminar ethene diffusion flames, both non-sooting and sooting, and laser diagnostic tests.