The factors affecting the important question of specifying "road octane number" of gasolines are associated both with the origin and method of refining of the fuel and with engine design characteristics. These are discussed together with the available bench and road test methods, and the correlation and limitations of the latter are considered.

More complete information is often needed than is given by the commonly used procedures and in consequence a new test method has been devised. This road test procedure, which is applicable to normal driving conditions in the U.K., can also be accurately simulated on the bench.

The behaviour of a number of fuel and engine types is discussed.


Les facteurs influençant la question importante de spécifier l'"indice d'octane routier" des essences tiennent à l'origine et à la méthode de raffinage du combustible aussi bien qu'aux caractéristiques de construction des moteurs. Ces données sont discutées ainsi que les méthodes d'essai actuelles au banc d'essai et sur la route et la corrélation et les limitations de celles-ci sont examinées.

Fréquemment on a besoin de données plus complètes que celles résultant des procédés usuels, de sorte qu'on a mis au point une nouvelle méthode d'essai. Ce procédé d'épreuve sur route, qui s'applique à des conditions normales de conduite dans le Royaume Uni, peut ëtre imité avec précision sur le banc.

Le comportement de quelques types de combustibles et de moteurs est discuté.


Although the phenomenon of "knocking" or "detonation" in internal combustion engines has been the subject of investigation for over thirty years, and the determination of octane number in the labora- * Ecco Development Co., Abingdon, Berkshire, U.K. tory by the C. F. R. Motor and Research methods has long been standardised, methods for the determination of "road octane number" and the "octane number requirement of cars" still vary widely. Unfortunately a knowledge of the laboratory octane numbers of a series of fuels does not enable an accurate prediction to be made of their relative performance on the road either in a given car under given conditions or even on a hypothetical average car.

Changed in engine design over a period alter the relative antiknock performance of different fuel types in currently available cars and variations between engines of different make, and even between different engines of the same model, lead to wide divergences in the octane number level of various types of fuel which will give knock-free performance.

Factors affecting detonation There are many factors which affect the occurrence of knocking in the automobile engine, the actual composition of the fuel and the engine design being of primary importance. The power-weight ratio of the car, the

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