  In order to better understand the importance of the different channels
leading to the first aromatic ring, we have investigated, the structure of a
laminar rich premixed methane flame doped with several unsaturated
hydrocarbons: allene and propyne, as they are precursors of propargyl radicals,
which are well known as having an important role in forming benzene,
1,3-butadiene, to put in evidence a possible production of benzene due to
reactions of C4 compounds, and, finally, cyclopentene, which is a source of
cyclopentadienyl methylene radicals which are supposed to easily isomerizes to
give benzene. A ratio additive / CH4 of 16 % and an equivalence ratio of 1.79
have been used. These flames have been stabilized on a burner at a pressure of
6.7 kPa using argon as dilutant. A new mechanism for the oxidation of allene,
propyne, 1,3 butadiene and cyclopentene has been proposed including the
formation and decomposition of benzene and toluene. The main reaction pathways
of formation of aromatics have been derived from flow rate analyses and have
been compared for the three types of additives.
