Fuel Anti-knock Requirements of Automobile Engines

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Abstract
While there are other approaches to the problem of improving overall efficiency, the paper discusses mainly the limits imposed by fuel anti-knock requirements on thermodynamic efficiency. After reviewing the basic concepts of knock and octane number, knowledge acquired during the 1939–45 war on aviation engines is summarized. The large production of aviation gasoline during the war gave rise to false hopes of a super-fuel for motor vehicles. Post-war fuel production difficulties due to shortage are mentioned, leading to the decision to construct refinery equipment in the United Kingdom. A brief description of this follows, and of the essential performance characteristics of the fuel. This leads to a discussion of octane requirements of automobiles, of temperature sensitivity of fuels, and of engine severity. Reference is made to the influence of the following engine design and operational factors on octane requirements: compression ratio, overhead versus side valve, mixture temperature, mixture strength and distribution, valve overlap, ignition advance, engine speed, coolant temperature, and combustion chamber deposits. It is concluded that, by increased cooperation in the United Kingdom between fuel suppliers and engine designers, much can be done to make better use of the fuels available now and in the coming years.

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