Effect of jacket temperature on oil engine performance

Abstract

The rate of combustion does not appear to be seriously influenced by the jacket temperature. There is of course a very considerable heat loss to the jacket when the latter is cold, as is shown in the Final Heat Balance, but it is probable that the major portion of this occurs during the exhaust stroke. Against this greater heat loss to the walls must, however, be credited the gain due to increased volume-:tric efficiency. As far as the power developed within the cylinder is concerned it may be said that the efficiency is not greatly affected by change in the , jacket temperature. The piston friction on the other hand is very considerably influenced by the jacket temperature, especially at light and moderate loads. This would appear to be due almost entirely to the change in the nature of the lubricating oil film with change in temperature. It is known that for most, if not all lubricating oils there is considerable variation in viscosity through a moderate range of temperature, and it may be suspected that as far as the piston friction is concerned this change in viscosity is the deciding factor.

Under the severe conditions imposed by the combustion of the fuel in the cylinder other influences may be introduced which would affect the piston friction to a greater or less degree, such as dilution and decomposition. The first of these would tend to reduce the viscosity of the lubricant, and the second would certainly be detrimental to the maintenance of the oil film. There are also many other disturbing influences but it is doubtful whether during the relatively short period of the tests the existence of any of these would be effective in altering the piston friction to any extent.

In conclusion, the author desires to acknowledge the many helpful suggestions received from Sir Thomas Hudson Beare.