A methane-air premixed flame with an equivalence ratio of 1.25 was simulated with a model including 91 pairs of elementary reactions occurring among 29 species. In this first work, the structure of a representative transversal section of the flame is presented and the mechanisms of combustion at the inner and outer cones are discussed in detail. CH4 and O2 in the mixture both react with H atoms, but the reaction between CH4 and H occurs preferentially to that between O2 and H at the fuel side of the inner cone. This results in a lack of oxygen atoms at the position where CH4 breaks into CH3 radicals and the reactions belonging to the C2 route proceed with higher velocities than those belonging to the C1 route. The consumption of O2, being posterior to the consumption of CH4, produces O atoms at the center of the inner cone. These O atoms, though not abundant, are sufficient to oxidize the last stable product of the C2 route, C2H2, preventing soot production. The diffusion of H atoms from the flame front to low-temperature regions and the subsequent production of OH radicals were found to be essential to the stability of both inner and outer cones, by triggering the combustion chain reactions.
|ジャーナル||Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B|
|出版ステータス||Published - 1995|
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