The combustion at about 1000°C of methane/air mixtures containing up to 5% of methane has been studied using a flow system. Under such conditions the reaction takes place in a few milliseconds. It is little influenced by surface, is retarded by methane and accelerated by oxygen. Below 500 to 600°C there appears to be a change in the kinetics, but no definite trend of apparent activation energy has been distinguished over the whole temperature range. The effect of surface on the reaction increases at lower temperatures. The reaction proceeds via formaldehyde and carbon monoxide, and the further oxidation of the latter is apparently inhibited by the former or by its oxidation products. This results in an accumulation, in the later stages of reaction, of carbon monoxide, which oxidizes rapidly or ignites when the formaldehyde and the methane have been consumed. Carbon dioxide does, however, appear to some extent before this final stage. Hydrogen also appears, and although its oxidation is retarded in the presence of methane, when the methane oxidizes the hydrogen goes ‘in step’ with it. In the presence of hydrogen the oxidation temperature of carbon monoxide is reduced to that of the hydrogen, but on addition of methane the hydrogen and methane are oxidized together, whilst carbon monoxide remains until the methane has disappeared. Ethane also inhibits the combustion of carbon monoxide, but less effectively than an equal amount of methane.
Controlled atmosphere GMAW welding of transportation vehicles and production machines parts made from 30MnB5 steel
