Abstract
A great deal of difficulty has been experienced in the reproduction of results obtained with small-scale accelerated engine tests used in classification of lubricating oils in the laboratory. The erratic results obtained are due to difficulties of standardizing conditions under which the tests are made. A number of factors make their variations manifest in the lubricating oil consumption rate, and a method has been developed which enables the oil consumption to be standardized when other easily controlled factors are maintained constant.
The rings are run-in with a base oil to which has been added approximately one per cent of tri-butyl phosphite, and efficient bedding of the rubbing surfaces is obtained within six hours.
The oil consumption rate is accurately measured throughout the run-in period, and the test is stopped when a standard oil consumption rate has been attained. The engine is then dismantled, cleaned with tri-chlorethylene and re-assembled for running with the test oil.
The oil consumption rate curve has been found, under these circumstances, to give an indication of the manner in which the rings are operating, that is, whether the oil and test conditions are such as to cause the rings to be working unsatisfactorily owing to incipient ring sticking, and also, the time at which a ring sticks completely in its groove.
The effect of brake mean effective pressure upon the ring-sticking propensity of an oil has been demonstrated in the paper, by comparing the oil consumption rate curves; and other factors which have been found to lead to erratic results have also been discussed.
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