The kinetics of the combustion of methane

The kinetics of oxidation of methane at pressures comparable with atmospheric pressure presents many features of great interest and of considerable importance to the elucidation of the nature of combustion processes in general. The facts which have accumulated to date, though fairly precise and definite, require in some cases amplification and further study in view of the realization that combustion has the character of a chain reaction. It has been found that the temperature of ignition of methane, which lies in the region 700-800°C., is dependent on the composition and total pressure of the mixture. For equimolecular mixtures of CH4 and O2 , no lower limit phenomena of the kind associated with hydrogen or carbon monoxide ignition have been observed. Below the ignition limit there is a readily measurable reaction velocity, and it was shown by Fort and Hinshelwood that the pressure-time curve is comprised of three distinct parts: (a ) an induction period of several seconds’ or minutes’ duration, during which almost no reaction can be detected; (b ) a period of acceleration to a steady velocity, followed by (c ) a gradual decline of the velocity to zero as the reactants are used up. Fort and Hinshelwood showed that the velocity during the reaction period was much more dependent on the pressure of methane than that of oxygen. They further established the fact that the reaction is almost completely inhibited by packing the vessel with pieces of quartz tubing. Bone and Allum showed that the most reactive mixture consists of methane and oxygen in the ratio 2:1, the induction period being shortest and the reaction velocity greatest for this proportion. It was further found that the reaction is subject to sensi­tization, small quantities of nitrogen peroxide, iodine, or formaldehyde practically removing the induction period and increasing the reaction rate. An analysis of the products of the reaction showed that it followed the general course: CH4 + 1½ O2 = 2H2 O + CO. (I)