Thermodynamic and kinetic issues in the formation and oxidation of aromatic species

The chemistry of aromatic species is discussed in the context of detailed kinetic modelling of benzene and butadiene flames and stirred reactors featuring ethylene and mixed aromatic/ethylene/hydrogen fuels. The development of reliable detailed mechanisms depends on the accuracy of the underlying hydrocarbon chemistry and the present paper highlights some current issues in the formation and oxidation of aromatics. In particular, uncertainties pertaining to the rates and product distributions of a range of possible naphthalene and indene formation sequences are discussed from the basis of improved predictions of key intermediates. The naphthalene formation paths considered include initiation via C5H5 + C5H5, C6H5 + C4H4 and C7H7 + C3H3 reactions and results are assessed in the context of a number of tentative detailed and simplified sequences. It is shown that a number of possible formation channels are plausible and that their relative importance is strongly dependent upon oxidation conditions. Particular emphasis is placed on the investigation of formation paths leading to isomeric C9H8 structures. The latter are typically ignored despite measured concentrations similar to those of naphthalene. The rates of formation of C9H8 compounds are consistent with sequences initiated by C6H5 + C3H3 and C6H5 + C3H4 leading to indene through repeated isomerisation reactions. The current work also shows that reactions of the type C9H7 + CH3 and C9H7 + (CH2)-C-3 provide a mass growth source that link five and six member ring structures.