The formation of C 2 hydrocarbons within methane-oxygen flames

Abstract

A molecular beam inlet into a quadrupole mass spectrometer is described. It has been used to study the concentrations of intermediate species formed within the primary reaction zone of low pressure methane-oxygen flames. In order to facilitate the analysis of the mass spectra, deuterated methane flames were burnt and the spectra obtained were compared with those from identical normal methane flames. This showed that ethane comld only be present within these flames in very low concentrations. Concentration profiles of CH 3 , CH 2 , CH 2 O, C 2 H 2 and C 2 H 4 through a flame are shown together with a temperature profile. The C 2 H 4 concentration is comparable with the CH 2 O concentration. Peak concentrations of all these species are given for a range of flames from =0.56 to 1.25. The peak C 2 H 4 concentration is shown to be related to [CH 3 ] 2 and the CH 2 peak is directly proportional to the CH 3 . This enables proposals for likely ethylene forming reactions to be made. C H 3 + C H 3 → C 2 H 4 + H 2 (2) C H 3 + C H 2 → C 2 H 4 + H The CH 3 and CH 2 concentration in these flames are in equilibrium via C H 3 + H ⇌ C H 2 + H 2 (7) This reaction followed by (3) is equivalent to reaction (2). From this work it is not possible to differentiate between (2) and (3). Literature values of the rates of these reactions show that one or both will become important reactive pathways in rich flames.