The oxidation of weak methane-air mixtures at high temperatures

Abstract

The motored engine technique for studying hydrocarbon combustion processes has been used by Downs, Street, Walsh and Wheeler ~, 2 for investigating cool flame formation, and by Pastell et al2, 4 and Levedahl et al. ~ to study precombustion reactions and cool flame limits. Detailed analyses of exhaust products obtained by this method have been made by Pahnke, Cohen and Sturgis ~ and have been discussed in relation to the appearance of cool flames. In addition, Melby 7 has used the method to study the effect of fuel additives on the precombustion reactions of nheptane. The experimental method is to introduce a fuel air mixture to a motored engine and observe the reaction while the compression ratio is slowly increased until auto-ignition occurs. In the present work, however, an engine of fixed compression ratio was used and the induced charge passed through a controlled electric heating system. The initial mixture temperature was therefore the experimental variable, and could be closely controlled during observation of the reactions. Closely related work on the oxidation of methane has been carried out by Burgoyne and Hirsch s using a heated tube, the temperature ranges are similar but pressures are very much lower (atmospheric as compared with approximately 30 atm in the present work) and residence time somewhat shorter. The ignition of methane when injected into a high temperature moving air stream has been studied by Mullins 9.