Morphology and mobility diameter of carbonaceous aerosols during agglomeration and surface growth

Agglomeration and surface growth of fractal-like carbonaceous aerosols in the absence of oxidation and condensation of volatiles are investigated by Discrete Element Modeling (DEM) from the free molecular to transition regime, accounting for primary particle polydispersity and chemical bonding (aggr...

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Bibliographic Details
Published in:Carbon (New York) 2017-09, Vol.121, p.527-535
Main Authors: Kelesidis, Georgios A., Goudeli, Eirini, Pratsinis, Sotiris E.
Format: Article
Language:English
Subjects:
Aerosols
Agglomeration
Aggregates
Bulk density
Carbon
Carbon black
Chemical bonds
Combustion
Condensation
Diffusion flames
Discrete element method
Effective density
Exhaust gases
Fractal dimension
Fractals
Mass-mobility exponent
Mathematical morphology
Mobility diameter
Oxidation
Polydispersity
Quenching (cooling)
Soot
Soot morphology
Volatile compounds
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Summary:Agglomeration and surface growth of fractal-like carbonaceous aerosols in the absence of oxidation and condensation of volatiles are investigated by Discrete Element Modeling (DEM) from the free molecular to transition regime, accounting for primary particle polydispersity and chemical bonding (aggregation). That way, carbon black or soot formation is elucidated in plasma reactors, quenched flames and combustion engines running at high exhaust gas recirculation where oxidation of carbon is limited or non-existent. During nascent soot formation polydisperse spheres and aggregates are formed, attaining an asymptotic geometric standard deviation of 1.2 ± 0.01, in agreement with experiments in premixed, diffusion flames and wood combustion. When surface growth stops, mature soot grows by agglomeration of these polydisperse spheres and aggregates before oxidation and condensation take over. The evolution from nascent to mature soot morphology quantified by its fractal dimension, Df, and mass-mobility exponent, Dfm, is in good agreement with measurements in premixed, diffusion flames and the Cast soot generator. The mobility diameter, dm, can be related to the average number of primary particles per agglomerate by nva = (dm/dva)0.45 and the relative effective density of soot by ρeff/ρs = (dm/dva)−0.78, where dva is the primary particle diameter and ρs the soot bulk density. [Display omitted]
ISSN:0008-6223
1873-3891
DOI:10.1016/j.carbon.2017.06.004