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

The chemistry of aromatic species is discussed in the context of detailed k inetic modelling of benzene and butadiene flames and stirred reactors featu ring ethylene and mixed aromatic/ethylene/hydrogen fuels. The development o f reliable detailed mechanisms depends on the accuracy of the underlying hy drocarbon chemistry and the present paper highlights some current issues in the formation and oxidation of aromatics. In particular, uncertainties per taining to the rates and product distributions of a range of possible napht halene and indene formation sequences are discussed from the basis of impro ved predictions of key intermediates. The naphthalene formation paths consi dered include initiation via C5H5 + C5H5, C6H5 + C4H4 and C7H7 + C3H3 react ions and results are assessed in the context of a number of tentative detai led and simplified sequences. It is shown that a number of possible formati on channels are plausible and that their relative importance is strongly de pendent upon oxidation conditions. Particular emphasis is placed on the inv estigation of formation paths leading to isomeric C9H8 structures. The latt er are typically ignored despite measured concentrations similar to those o f naphthalene. The rates of formation of C9H8 compounds are consistent with sequences initiated by C6H5 + C3H3 and C6H5 + C3H4 leading to indene throu gh repeated isomerisation reactions. The current work also shows that react ions of the type C9H7 + CH3 and C9H7 + (CH2)-C-3 provide a mass growth sour ce that link five and six member ring structures.