Abstract
In the course of use an engine lubricating oil becomes contaminated with the products of its own breakdown, and with others derived from incomplete combustion of the fuel, leading to objectionable deposits influenced not only by the characteristics of the lubricant but also by other factors such as engine design, operating conditions, and maintenance. Fuel characteristics—such as volatility, ignition quality, and sulphur content—affect lubricating oil behaviour. The effect of viscosity on fuel consumption is explained. Increase in engine output for a given weight and size, together with operation at high temperature and load, have an adverse effect. Results obtained from service tests with an oxidation-inhibited oil and with a fully-detergent (“heavy duty”) oil are described, and examples are given of the use of data obtained by examination of used oils, considered in conjunction with statistics derived from a study of the condition of the engines.
Physical specifications for non-additive type lubricants can be compiled to define oils which have proved satisfactory. The present position in Great Britain regarding specifications for detergent (H.D.) oils is reviewed; conventional specifications are inadequate to describe this type of lubricant, the behaviour of which can be determined only by engine tests.
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