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Updated: Dec 27, 2025
Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes
Published on: May 26, 2014
On the mechanism of soot nucleation
Michael Frenklach1, Alexander M Mebel2
1Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA. frenklach@berkeley.edu.
Abstract:
The mechanism of carbon particulate (soot) inception has been a subject of numerous studies and debates. The article begins with a critical review of prior proposals, proceeds to the analysis of factors enabling the development of a meaningful nucleation flux, and then introduces new ideas that lead to the fulfillment of these requirements. In the new proposal, a rotationally-activated dimer is formed in the collision of an aromatic molecule and an aromatic radical; the two react during the lifetime of the dimer to form a stable, doubly-bonded bridge between them, with the reaction rooted in a five-member ring present on the molecule edge. Several such reactions were examined theoretically and the most promising one generated a measurable nucleation flux. The consistency of the proposed model with known aspects of soot particle nanostructure is discussed. The foundation of the new model is fundamentally the H-Abstraction-Carbon-Addition (HACA) mechanism with the reaction affinity enhanced by rotational excitation.
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