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Abstract
The concentration profiles of polycyclic aromatic hydrocarbons (PCAH) and perinaphthenyl radical along a vertical flow reactor have been determined for fuel rich premixed flames of n-heptane with small fractions of other hydrocarbons, methanol, and nitrogen oxide.
It has been found that there is a strict relation between the concentrations of the higher molecular weight PCAH, which are the main components of soluble fraction of soot, and the perinaphthenyl radical.
The aromatic ring of the fuel supplying the reactor plays the most significant role in the formation of PCAH and perinaphthenyl radical. Furthermore their concentrations increase passing from benzene toluene and, lastly, to mesitylene, because the energy of the C(arom)-C(alif) bond is lower than that of the C(arom)-C(arom) bond.
The promoting action of methanol, when added to benzene, in the formation of PCAH and perinaphthenyl radical could be explained by the increased presence of CH3- radicals, which, can overcome the inhibiting action of OH- radicals. The contrary happens when methanol is added to toluene, because CH3- coming from alcohol represents only a small fraction of the overall concentration, while the oxidant activity of OH- is prevailing, Finally the strong action of NO in reducing the free radical concentration has been pointed out.