Abstract
Soot formation processes have been studied for more than 100 years, they include empirical and phenomenological description of conversion of various fuels to soot particles. This article provides an overview of current state of soot formation foundations, including the chemistry of soot nucleation, nucleation, mass growth as well as size of soot particles. Consideration of this issue shows that a great progress has been made, but there is still a lot of ambiguity in many areas of our knowledge. This concerns the role of aromatic molecules and radicals in nucleation and subsequent growth mass in laminar pre-mixed flames. Along with environmental problems, in recent time there are considered soot particles as an environment for nanomaterial synthesis, such as fullerenes, carbon nanotubes and graphenes. In this regard, a complete scheme of nanomaterials formation in mode of soot formation has been developed.
Highlights
At the present time a large number of experimental data on soot formation processes have been accumulated and different phenomenological models have been proposed [1,2,3,4,5,6]
Frenklach and Wang [7] proposed that aromatic hydrocarbons once formed, aromatic rings grow by a sequential two-step process: H-abstraction which activates the aromatic molecules, and acetylene addition which propagates molecular growth and cyclization of polycyclic aromatic hydrocarbons (PAHs)
Frenklach and Ebert [20] suggest that the number of the bent structures, i.e., PAHs containing five- and six-membered rings, increase successively, which leads to the formation of fullerenes
Summary
At the present time a large number of experimental data on soot formation processes have been accumulated and different phenomenological models have been proposed [1,2,3,4,5,6]. Frenklach and Wang [7] proposed that aromatic hydrocarbons once formed, aromatic rings grow by a sequential two-step process: H-abstraction which activates the aromatic molecules, and acetylene addition which propagates molecular growth and cyclization of PAH. This H-abstraction – C2H2-addition reaction sequence as HACA (Fig. 2). I.e., with transition to atmospheric pressure or above, where triple collisions dominate, PAHs coagulate to form soot clusters It has been shown [15] that the maximum of fullerene formation is shifted to the right relative to the maximum of soot formation. The relative contribution to particle growth of small hydrocarbon species and larger aromatic molecules depend on the process conditions. The number of particles decreases, while the overall mass remains unchanged
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