Abstract
In order to understand the fundamental mechanism of combustion processes, it is necessary to measure the concentrations of all the species throughout the flame front. Molecular beam sampling and mass spectrometric analysis have been used for that purpose. We have determined the molar concentrations of the stable and unstable species for two C 2 H 2 /O 2 flames: a lean flame and a stoichiometric one. Both flames were burning at 40 Torr. From all these data, it is possible to deduce the elementary processes occurring in acetylene combustion. The first step of acetylene removal involves either hydroxyl radicals or oxygen atoms, in different proportions depending on the equivalence ratio: C 2 H 2 +O→CO+CH 2 (r.11) k 11 =6.7×10 13 exp(−4000/RT)cm 3 mol −1 s −1 C 2 H 2 +OH→C 2 H 2 O+H(r.8) k 8 =3.2×10 11 exp(−200/RT)cm 3 mol −1 s −1 . The CH 2 radical then reacts with molecular oxygen, producing carbon dioxide and molecular hydrogen. The ketene C 2 H 2 O reacts with a hydroxyl radical to form formaldehyde: C 2 H 2 O+OH→CH 2 O+CHO (r.7) k 7 =2.8×10 13 cm 3 mol −1 s −1 , and CH 2 O further reacts with another hydroxyl radical: CH 2 O+OH→CHO+H 2 O Molecular oxygen then combines with the formyl radical CHO to give carbon monoxide: CHO+O 2 →CO+HO 2 The CO and H 2 , formed in the combustion of acetylene, disappear through the usual elementary reactions.
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