ISSN:
1573-2932
Source:
Springer Online Journal Archives 1860-2000
Topics:
Energy, Environment Protection, Nuclear Power Engineering
Notes:
Abstract Highly divided C can be formed by heat treatment of hydrocarbons in absence of O (thermal decomposition) or in its presence (flames). This variety of C, named soot or carbon black, has a considerable polluting effect. Moreover, considering the increasing cost of energy sources, energy loss under the form of unburnt species has to be reduced. To decrease or to suppress soot formation, it is often necessary to know the mechanism of formation and, in particular, the phenomena involved in the nucleation step. The mechanism of soot formation in flames is basically identical in premixed flames and in diffusion flames. However, as the different chemical stages are well separated, from a spatial point of view, in premixed flames, most investigations deal with this type of flame. In the oxidation zone of the flame (blue zone), a part of the hydrocarbon is burnt out while another part undergoes complex reactions leading to polyacetylenes and later to polycyclic hydrocarbons with lateral chains. In the same region, ions are formed by chemiionization. In the zone of formation of C particles (yellow zone), polycyclic hydrocarbons are dehydrogenated and give polyaromatic hydrocarbons; their partial pressure increases until they reach a supersaturation high enough to induce nucleation of liquid microdroplets. The microdroplets are formed by homogeneous nucleation as well, probably, as the nucleation on the positive ions formed in the oxidation zone of the flame; they are converted by growth, association and chemical transformation into solid soot particles. In thermal systems, the mechanisms involved are identical except that nucleation on ions may be disregarded. In both systems, nucleation of microdroplets is a fast and discontinuous phenomenon. Such an understanding in C particle formation might be efficiently used to reduce noticeably atmospheric pollution and energy loss by soot formation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00341000
