Chemistry of otto-cycle engine combustion

Abstract

Chemical study of internal-combustion engines is amply justified from the theoretical as well as the practical point of view. Aside from their obvious economic importance, engines have provided a wealth of information regarding the nature of combustion, much of it unattainable with other conventional forms of laboratory equipment. In return, the interpretation of these results has been--and to a largc extent still is--a complex problem which challenges those chemists who are interested in the general theory of the subject. Nevertheless, it seems fair to say that, until recently, there has been in general a lack of effective cooperation between the chemists on one hand and tile engineers on the other, and advances in the theory of eigine combustion have been slow. This seems to have been due largely to a tendency, on both sides, to oversimplify the problem. Chemists have made numerous labora~ tory experiments under conditions not remotely resembling those of an engine, but the results were applied, without criticism, directly to engine combustion; at the same time no detailed analysis has been made of the chemical facts furnished by the engine itself. On the other hand, engineers have been largely occupied with the practical development and testing of engines and fuels, with little or no direct investigation of the chemical theory of the subject. Recent years have seen considerable improvement in these respects. Chemical experimentation conducted dircctly with engines or closely related apparatus has given a series of facts to replace uncertain assumptions; simultaneously, the development of the chain reaction theory of the slow oxidation and explosion of gases has provided a reasonable basis for the explanation of the phenomena observed. As a result, it is now possible to advance a general outline of the nature of engine combustion which is in accord with the known facts and appears to be theoretically sound. At the same time, a great many details remain to be filled in and a number of major points are still in doubt. It is the purpose of this paper to present, briefly, such an outline, to indicate some of the respects in which our knowledge is still deficient, and to emphasize further the relative complexity of engine combustion. It is hoped that this survey will to some degree promote better appreciation of the problem and encourage still more effective cooperation between the chemists and engineers who are concerned with it. We shall consider in our survey only the Otto-cycle engine, since the Diesel engine will be dealt with in other papers of this symposium. No attempt will be made to refer to the extensive literature on the subject, either in its entirety or specifically. (For recent selected bibliographies see the appropriate sections of Science of Petroleum, Oxford University Press (1937), Proceedings of the Second World Petroleum Congress, Paris, 1937, and this Symposium; also References 1, 2, and 3.) Only those data and conclusions which have been instrumental in establishing our present conception of the subject have been selected; their interpretation is the present author's personal one, but appears to be in general accord with the consensus of opinion.