Formation of flame ions, clusters, nanotubes, and soot in hydrocarbon flames

The actual work deals with the present state of research on flame ions, polyaromatic hydrocarbons, nanotubes, fullerenes, and soot particles in premixed flames. Experimental arrangements for detection and quantitative investigation of flame ions are presented. In addition, the influence of ions on flame chemistry and on formation of carbon particles under non-sooting and sooting conditions is discussed. The study also focuses on the formation pathway from flat polyatomic hydrocarbons to fullerenes, nanotubes, and soot particles. In this connection, the features of arched “aromers”, which are high reactive metastable species and leading candidates for soot precursors and fullerene formation, are reported. These aromers seem to be a kind of “switch” capable of producing either fullerenes or soot particles, depending on the reaction conditions. At lower flame temperatures and a high number density of small unsaturated hydrocarbons, bimolecular reactions are favored, and the formation of soot particles exceeds that of fullerenes. It is also shown how the further growth of soot particles can be described, namely, by soot mass growth and by coagulation processes in strong sooting flames. Typical values for soot volume fractions and particle diameters under various reaction conditions are given.