[Plates 33-35.] As part of tbe general investigation of the initial stages of gaseous explosions now being carried on by us at the Imperial College, London, we have had occasion to study photographically the behaviour of an equimolecular methane-oxygen mixture when ignited by sparks of varying intensities passed between electrodes fixed half-way along a horizontal glass tube (35 to 50 cms. long by 2 to 2 • 5 cms. diameter), both ends of which were dosed in one series of experiments, but open in another. A few supplementary experiments were also made under other spark igniting conditions. The results of these experiments seem to be of sufficient importance, from the point of view of the interpretation of the initial stages of gaseous explosions, as to justify the separate publication of them at this juncture.The evidence of the experiments lies so much in the photographs themselves that little need be said about them beyond indicating the precise conditions under which they were obtained. It is left to each reader to study them for himself, because, while their main features will be obvious to all, the inter pretation leaves room for discussion, which it is hoped this publication will provoke.To us they suggest such possibilities as (a) the occurrence, under ordinary sparking conditions, of what seems to be much like a definite induction period ' as a preliminary to the actual combustion; ( ) an initial propagation through the medium of a " ghost-like flame " condition involving only a very partial combination of the gases; and (c) the main combustion following later as the result of the superposing of a compression wrave, or the like, upon a system which during the phase (b) has already become highly sensitive to chemical changes.Experimental.
MUCH has been written concerning the action of heat on hydrocarbons, and the separation of carbon in flames, since Dalton and William Henry conjointly studied the decomposition of methane and ethylene when subjected to t h e continued action of electric sparks (Dalton's "New System," vol. I, pp. 440, 447; Phil. Trans., 1809, 99, 446).Owing, however, to the complexity of the phenomena, and the difficulty in realising conditions under which crucial evidence can be obtained, we are still far from understanding the precise modes of decomposition of even the simplest hydrocarbons, whilst the final elucidation of the question as i t affects the higher members of the various series will probably tax our experimental resources to the utmost for many years to come.That the ultimate resolution of a hydrocarbon into its elements at high temperatures cannot be regarded in general a s the immediate result of a single chemical change was proved by Marchand in IS39 (J. pr. Chem., 36, 478>, when he obtained large quantities of methane during the decomposition of ethylene a t a bright red heat. This led him to represent the initial stage of the transaction as invoIving the simultaneous liberation of carbon and methane as follows :This view derived some support from the later observation of Buff and Hofmann (Annalen, 1860, 113, 129), t h a t when a platinum wire is electrically heated+to dull redness in ethylene, the gas is decomposed, yielding carbon and much methane without any appreciable change in volume. But the cogency of this otherwise important piece of evidence * A preliminary notice of this investigation appeared under the names of Bone Entre' chaque genre de reaction et la reaction rkiproque il s'btablit frequemment line sort d'bquilibre mobile, variable avec la temperature e t les corps qui se trouvent en prdsence, Bqnilibre analogue B celui qui se prodnit lors la dissociation des composes binaires."
View Article Online / Journal Homepage / Table of Contents for this issue COMBUSTION OF HY1)ROCARBONS. 661 explosive combustion * of a number of different gaseous hydrocarbons, including members of the saturated series C12H2jL+z, up to butane, olefines such as ethylene, propylene, and the butylenes, as well as trimethylene and acetylene. Among the new facts brought to light during the research, me need now only refer to those which appear to be crucial as regards the two theories under discussion. Considering, in the first place, the end result obtained when explosive combustion occurs in the system C,H, + x / 2 0 2 , we have discovered a remarkable difference between the behaviour of a n olefine and that of the corresponding paraffin. I n the case of a n olefine, there is no separation of carbon, and very little (if any) formation of steam, the cooled products consisting chiefly of carbon monoxide and hydrogen, in accordance with the empirical equation : CnH2, + 4 2 0 2 = mC0 + 1zH2. I n the case of bhe corresponding paraffin, however, there is always a considerable separation of carbon and a large formation of steam. The gaseous products contain, besides carbon monoxide and hydrogen, between 8 and 10 per cent. of methane, and fair proportions both of unsaturated hydrocarbons (acetylene and ethylene), and of carbon dioxide. Evidently, therefore, the theory of the preferential combustion of carbon in hydrocarbon flames does not apply to the case of a saturated hydrocarbon. But it will be shown that the theory also breaks down when the case of a n olefine is more closely examined. For whilst i t is true that the end-products obtained when a mixture C,Hzn + $202 is exploded conform to the requirements of the theory, we find that if the proportion of oxygen in the original mixture is further diminished, much water, a s well as carbon, is produced. Indeed the quantity of water formed increases as the supply of oxygen is reduced below the above limit, The same thing also applies in the case of trimethylene. This characteristic behaviour of members of the Cp,H2, series obviously does not harmonise with the theory in question, but it is easily explained if the initial formation of hydroxylated products in hydrocarbon flames be admitted. Comparative experiments on the oxplosion of paraffins with oxygen in proportions indicated by the general expression CnHenfZ + n/20,, and of mixtures of the corresponding olefines with hydrogen and +t The terms " explosive com?rustion '' and " explosion," as applied to gaseous mixtures, are perhaps somewhat ambiguous. They are often used indiscriminately to denote both the propagation of a flame through a combustible mixture under ordinary conditions ((' ir$amnzation "), and also the conditions existing when an explosion wave is set up ("detonation"). It must be clearly understood that, throughout this paper, the terms in question are used in the former sense only.
In Part VI of this series, the results of photographic investigations into the phenomenon of “ spin ” in gaseous detonations up to June 1931 were described, and it was stated that further experiments were in hand, particularly as regards the effects of strong electric and magnetic fields upon the phenomenon, because it had already become evident “ that the present theory of detonation in gaseous media needs revision.” Since that time we have been continuously investigating the matter, and have now reached a new view of it which will be set forth herein. Before this can be done, however, it is necessary briefly to review the position three years ago when Part VI was published.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.