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For a better modeling of the importance of the different channels leading to the first aromatic ring, we have compared the structures of laminar rich premixed methane flames doped with several unsaturated hydrocarbons: allene and propyne, because 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 cyclopentadienylmethylene radicals which in turn are expected to easily isomerizes to give benzene. These flames have been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as dilutant, for equivalence ratios (?) from 1.55 to 1.79. A unique mechanism, including the formation and decomposition of benzene and toluene, has been used to model the oxidation of allene, propyne, 1,3 butadiene and cyclopentene. The main reaction pathways of aromatics formation have been derived from reaction rate and sensitivity analyses and have been compared for the three types of additives. These combined analyses and comparisons can only been performed when a unique mechanism is available for all the studied additives.

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., Comment: European Combustion Meeting, Chania : Gr\`ece (2007)

In line with the studies presented in the parts I and II of this paper, the structure of a laminar rich premixed methane flame doped with cyclopentene has been investigated. The gases of this flame contains 15.3% (molar) of methane, 26.7% of oxygen and 2.4% cyclopentene corresponding to an equivalence ratio of 1.79 and a ratio C5H8 / CH4 of 16 %. The flame has been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The temperature ranged from 627 K close to the burner up to 2027 K. Quantified species included usual methane C0-C2 combustion products, but also propyne, allene, propene, propane, 1-butene, 1,3-butadiene, 1,2-butadiene, vinylacetylene, diacetylene, cyclopentadiene, 1,3-pentadiene, benzene and toluene. A new mechanism for the oxidation of cyclopentene has been proposed. The main reaction pathways of consumption of cyclopentene and of formation of benzene and toluene have been derived from flow rate analyses.

In line with the study presented in the part I of this paper, the structure of a laminar rich premixed methane flame doped with 1,3-butadiene has been investigated. The flame contains 20.7% (molar) of methane, 31.4% of oxygen and 3.3% of 1,3-butadiene, corresponding to an equivalence ratio of 1.8, and a ratio C4H6 / CH4 of 16 %. The flame has been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The temperature ranged from 600 K close to the burner up to 2150 K. Quantified species included usual methane C0-C2 combustion products and 1,3-butadiene, but also propyne, allene, propene, propane, 1,2-butadiene, butynes, vinylacetylene, diacetylene, 1,3-pentadiene, 2-methyl-1,3-butadiene (isoprene), 1-pentene, 3-methyl-1-butene, benzene and toluene. In order to model these new results, some improvements have been made to a mechanism previously developed in our laboratory for the reactions of C3-C4 unsaturated hydrocarbons. The main reaction pathways of consumption of 1,3-butadiene and of formation of C6 aromatic species have been derived from flow rate analyses. In this case, the C4 route to benzene formation plays an important role in comparison to the C3 pathway.

The structure of a laminar rich premixed 1,3-C4H6/CH4/O2/Ar flame have been investigated. 1,3-Butadiene, methane, oxygen and argon mole fractions are 0.033; 0.2073; 0.3315, and 0.4280, respectively, for an equivalent ratio of 1.80. The flame has been stabilized on a burner at a pressure of 6.7 kPa (50 Torr). The concentration profiles of stable species were measured by gas chromatography after sampling with a quartz probe. Quantified species included carbon monoxide and dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne, allene, propene, cyclopropane, 1,3-butadiene, butenes, 1-butyne, vinylacetylene, diacetylene, C5 compounds, benzene, and toluene. The temperature was measured thanks to a thermocouple in PtRh (6%)-PtRh (30%) settled inside the enclosure and ranged from 900 K close to the burner up to 2100 K., Comment: traduit de Fizika Goreniya I Vzryva, 2006, 42, 89-95

The structure of three laminar premixed rich flames has been investigated: a pure methane flame and two methane flames doped by allene and propyne, respectively. The gases of the three flames contain 20.9% (molar) of methane and 33.4% of oxygen, corresponding to an equivalence ratio of 1.25 for the pure methane flame. In both doped flames, 2.49% of C3H4 was added, corresponding to a ratio C3H4/CH4 of 12% and an equivalence ratio of 1.55. The three flames have been stabilized on a burner at a pressure of 6.7 kPa using argon as dilutant, with a gas velocity at the burner of 36 cm/s at 333 K. The concentration profiles of stable species were measured by gas chromatography after sampling with a quartz microprobe. Quantified species included carbon monoxide and dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne, allene, propene, propane, 1,2-butadiene, 1,3-butadiene, 1-butene, isobutene, 1-butyne, vinylacetylene, and benzene. The temperature was measured using a PtRh (6%)-PtRh (30%) thermocouple settled inside the enclosure and ranged from 700 K close to the burner up to 1850 K. In order to model these new results, some improvements have been made to a mechanism previously developed in our laboratory for the reactions of C3-C4 unsaturated hydrocarbons. The main reaction pathways of consumption of allene and propyne and of formation of C6 aromatic species have been derived from flow rate analyses.