MODELLING OF RICH PREMIXED ETHYLENE AND BENZENE FLAMES V. Dias * , J. Vandooren Laboratoire de Physico-Chimie de la Combustion, Université catholique de Louvain, Belgium dias@chim.ucl.ac.be Polycyclic Aromatic Hydrocarbons (PAHs) are formed in most combustion systems and play an important role in soot formation. Previously, we have developed a reaction mechanism validated against premixed rich C 2 H 4 /O 2 /Ar flames (φ = 2.25 and 2.50) which describes in detail the formation of soot precursors and the main pathways involving benzene. The detailed mechanism involving 78 chemical species with the naphthalene as the heaviest and 405 elementary reactions [1, 2] has been slightly modified to taking into account recent kinetic parameters. The aim of this work is to check the reliability of this mechanism in a rich premixed benzene flame (φ = 2.00) [3], when the initial hydrocarbon is the first aromatic ring. In rich ethylene flames, the reaction mechanism is reasonably successful in predicting mole fraction profiles for key intermediate species, including aromatic molecules, in the equivalence ratio range from 2.0 to 2.5. The formation of the heavier species is analysed in detail. The fulvene is the key intermediate of the benzene formation. Phenyl radicals are mainly produced by hydrogen abstraction from benzene and by reaction of n- C 4 H 3 with acetylene. According to the kinetic model, benzene (C 6 H 6 ) and phenyl radicals (C 6 H 5 ) are important precursors for the formation of other aromatics like phenol (C 6 H 6 O), toluene (C 7 H 8 ), phenylacetylene (C 8 H 6 ) and styrene (C 8 H 8 ). Cyclopentadiene (C 5 H 6 ) produced mainly through the reaction of propyne (p-C 3 H 4 ) with vinyl radicals (C 2 H 3 ) plays also an important role in the formation of heavy hydrocarbons. Indeed, cyclopentadiene can loose an hydrogen to produce cyclopentadienyl radicals (C 5 H 5 ) which react between themselves to form naphthalene (C 10 H 8 ). The formation of indene (C 9 H 8 ) remains unclear but a new pathway involving cyclopentadiene and acetylene seems could be more adequate. In the rich benzene flame, the model predicts a very good agreement of mole fraction profiles with the experimental results for species: O 2 , C 6 H 6 , CO 2 , CO, H 2 , H 2 O, C 2 H 2 , C 3 H 3 , C 3 H 4 and C 5 H 6 . For heavier species, the simulated profiles overpredict the experimental ones: C 6 H 6 O (86.9 %), C 7 H 8 (45.7 %), C 8 H 6 (76.7 %), C 9 H 8 (79.9 %) and C 10 H 8 (82.6 %), at the peak of the profiles. These results can be justified by the kinetic mechanism modelling species only until the naphthalene (C 10 H 8 ). The mole flux analysis indicates that benzene and phenyl radicals are directly responsible for the formation of aromatic compounds like C 6 H 6 O, C 7 H 8 , C 8 H 6 and C 8 H 8 . Moreover, the acetylene (C 2 H 2 ) is mainly produced from the decomposition of phenyl radicals. Then, benzyl radicals (C 7 H 7 ) react with acetylene to form the indene (C 9 H 8 ). Cyclopentadienyl radicals (C 5 H 5 ), mainly produced from the decomposition of phenoxy radicals (C 6 H 5 O), react between themselves to form naphthalene (C 10 H 8 ). The original model has been validated in rich premixed ethylene flames and we have already extended its reliability to various hydrocarbon burning flames at several equivalence ratios: for less rich ethylene flames (φ = 1.0 to 2.0) as well as for rich methane (CH 4 ), acetylene (C 2 H 2 ) and ethane (C 2 H 6 ) flames in the equivalence ratio range from φ = 1.0 to 2.0 [4]. The extension of this kinetic mechanism to rich benzene flames has been successfully, even if this model should be completed with reaction pathways including larger PAHs to improve the modelling of heavier hydrocarbons. Acknowledgements The authors are very grateful to the Ministère de la Région Wallonne (Belgium) for the financial support (Visa n°04/45786). References [1] V. Dias, Etude de la Formation des Précurseurs des Suies dans les Flammes Riches Prémélangées d’Ethylène, PhD Thesis Université catholique de Louvain, Belgium, 2003. [2] V. Dias, C. Renard, P. J. Van Tiggelen and J. Vandooren, European Combustion Meeting, Orléans – France, p.221 (2003). [3] F. Defoeux, V. Dias, C. Renard, P. J. Van Tiggelen and J. Vandooren, Proceedings of the Combustion Institute 30 (2005) 1407-1415. [4] V. Dias, P. J. Van Tiggelen and J. Vandooren, European Combustion Meeting, Louvain-la-Neuve – Belgium, p.3 (2005).