The Effect of Base Stock Composition on Lubricant Performance

From detailed studies of the changes in base oil composition which occur during service, and by relating these changes to the accepted mechanisms of hydrocarbon autoxidation, it appears possible to select key base stock compositional parameters which generally predict the relative performance of formulated products in standard industry tests. The relevant compositional parameters depend, however, on the specific test method: tests which finish before the added inhibitor is entirely depleted are controlled primarily by the concentration of saturated hydrocarbons in the base stock; those which finish after disappearance of the inhibitor (e.g., Sequence IIID) are influenced more by the hydroperoxide decomposing components (mainly sulphur compounds) in the base stock.

By applying this understanding of lubricant oxidation, good correlations with base stock composition are being obtained for a variety of bench engine and laboratory oxidation tests including the Sequence IIID, Sequence V-D and Caterpillar 1H2, as well as the ASTM D2272 and D943 tests.