ON THE COOL FLAMES OF METHANE

Methane is an attractive alternate fuel. It burns cleanly and is resistant to ''knock.'' For many years methane was believed not to give rise to the phenomenon of cool flame, a process basic to the problem of ''knock'' in internal combustion engine. This paper shows that methane exhibits the same combustion events as those observed in higher hydrocarbons: slow combustion; production of hydrogen peroxide; multistage, low temperature ignition; single and multiple cool flames; regions of negative temperature coefficient; and high temperature ignition. The ignition diagrams are normal, but the cool-flames regions are found at higher temperatures and are much narrower than for higher hydrocarbons. This is the reason why the methane cool flames escaped experimental observation for such a long time. These findings give a rationale for the high, but not absolute, resistance of methane to ''knock.''