Soot Formation in the Buoyancy-Dominated Ethane Diffusion Flame.
Soot Formation in the Buoyancy-Dominated Ethane
Diffusion Flame.
(1095 K)
Subramaniasivam, H.
NIST GCR 92-609; 46 p. July 1992.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Order number: PB92-213396
Keywords:
soot; soot formation; diffusion flames; fuel flow rate;
air flow; sampling; ethylene; predictive models; laminar
flames; lasers; particle size
Abstract:
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899