Aerosol Dynamic Processes of Soot Aggregates in a Laminar Ethene Diffusion Flame.
Aerosol Dynamic Processes of Soot Aggregates in a
Laminar Ethene Diffusion Flame.
(1120 K)
Puri, R.; Richardson, T. F.; Santoro, R. J.; Dobbins, R.
A.
Combustion and Flame, Vol. 92, No. 3, 320-333, February
1993.
Sponsor:
Air Force Office of Scientific Research, Fort Monmouth,
NJ
Keywords:
diffusion flames; laminar flames; aerosols; soot; data
analysis; soot aggregates
Abstract:
Laser scattering/extinction tests on a coannular ethene
diffusion flame were analyzed using cross sections for
polydisperse aggregates. Using an improved experimental
arrangement that allowed simultaneous measurement of
light scattering at multiple angles, it was possible to
determine the fractal dimension of the aggregates in the
flame. The analysis also yields the mean-square radius
of gyration, the aggregate number concentration, the
average number of primary particles per aggregate, as
well as the volume average of the volume-mean diameter
as a function of height of residence time along the
particle path of maximum soot concentration in this
flame. These results lead to the conclusion that soot
aerosol dynamic processes in the laminar ethene flame
are partitioned into four regions. Low in the diffusion
flame there is a region of particle inception that
establishes the number of primary particles per unit
volume that remains constant along a prescribed soot
pathline. In the second region, there is sustained
particle growth through the combined action of
cluster-cluster aggregation (CCA) accompanied by
heterogeneous reactions contributing to monomer-cluster
growth. Oxidation processes occur in the third region
where CCA continues. If aggregate burnout is not
complete in the oxidation region, then smoke is released
to the surroundings in the fourth region where reactions
cease but clusters continue to grow by CCA. The
experiments yield the CCA growth rate within the flame
which compares favorably with the theoretical value.
The similarities and differences between this data
reduction and the traditional analysis based on the use
of cross sections for Rayleigh spheres and Mie theory
spheres is discussed.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899