ABSTRACT.

The fundamental factors influencing autoignition and surface ignition are discussed in teks of the ignition delay theory of Semenoff. These factors are then related to the practical problems of knock, hot starting noise, silent knock, preignition induced knock, knock induced preignition, and engine roughness, sometimes called rumble or pounding. In the absence of catalytic effects, it would appear that these phenomena are all related to the ignition delay characteristics of the fuel as determined in rapid compression machines. The controlling factor in knock appears to be autoignition irrespective of whether this is followed by rapid burning or detonation. A mechanism is given whereby apparent combustion wave velocities below detonation velocities, but well above normal turbulent flame speeds, can be formed. The effects of pressure, or density, and temperature on ignition delays is discussed with respect to the important reversals in the order of rating of fuels under different conditions. When ignition is catalyzed by surfaces, the situation becomes more complex, it being indicated that a catalytic surface may either increase or reduce the normal surface ignition tendency of a fuel as compared to the effect of a noncatalytic surface. When the catalytic sources contain combustible solids their effect may be transient in nature and dependent on their past history both as regards operating conditions and fuels and lubricants employed. A classification of catalytic surfaces is given on this basis. The available information is employed to explain the abnormal combustion phenomena observed in current engines and to predict the future significance of these problems in automotive engines.

RESUME.

Le mémoire traite, selon la théorie de Semenoff concernant le retard à l'allumage, des facteurs fondamentaux agissant sur l'auto-allumage et l'allumage de surface. Ces facteurs sont ensuite rapportés aux problèmes pratiques du cognement, du bruit chaud de mise en marche, du cognement silencieux, du cognement causé par l'avance à l'allumage, d'avance à l'allumage produite par le cognement, et des bruits dus au "moteur qui ne tourne pas rond" appelés "rumble" aux Etats-Unis.

En l'absence d'effets catalytiques, il semblerait que ces phénomènes soient tous dépendants des caractéristiques du retard à l'allumage du carburant, tel qu'il se produit dans les machines à compression rapide. Le facteur décisif en ce qui concerne le cognement, paraît être l'auto-allumage, qu'il soit suivi d'une combustion rapide ou d'une détonation. Le mémoire décrit le mécanisme par lequel les vitesses apparentes de turbulence peuvent se former au-dessous des vitesses de détonation, mais bien au-dessus des vitesses normales des flamm

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