Gaseous combustion in electric discharges.— Part I. The com­bustion of electrolytic gas in direct current discharges

Abstract

In connection with the researches upon various aspects of gaseous combus­tion which are being carried out in the Department of Chemical Technology, Imperial College of Science and Technology, South Kensington, one of us (C. I. F.) has undertaken a systematic investigation of the mechanism of com­bustion as initiated by, or occurring in, electric discharges. The present paper embodies the results of our experiments upon the combustion of electrolytic gas in direct-current discharges. Three phases have been distinguished in the process of gaseous combustion, namely, (i) a slow (non-self-propellant) combustion below the ignition point, (ii) a self-propellant flame propagation, and (iii) sometimes, also, a short preflame period during which combustion is self-propellant. The point at which he process becomes self-propel ant is sometimes termed the “ignition point.” Before combustion can be determined in it, however, energy in some form or other must be imparted to a given combustible system from an external source. Frequently, heat energy is so supplied, in which case it is customary to speak of an ignition temperature; on the other hand, electrical energy may be supplied, e. g ., by a spark, in which case we speak of a minimum igniting energy or minimum igniting current being necessary to make the combustion self­ propellant. In such conditions, whilst the self-propellant stage of combustion is usually determined by the purely electrical properties of the discharge employed (even though it may be affected by other influences, such as pressure waves emanating therefrom), yet, having once been set up, it is subsequently propagated through the system independently of such properties. On the other hand, the pre-ignition or non-self-propellant stage is throughout intimately associated with and determined by the discharge itself. Hence, an experimental examination of the influence of electric discharges upon the pre­ignition stage of combustion in gaseous mixtures may be expected to reveal the nature and mechanism of electrical ignition, and indeed of the process of combustion as a whole.