Low-Temperature Degradation of Lubricant Oil for Gasoline Engine

摘要

To clarify degradation characteristics of gasoline engine oil, we examined the influence of oil temperature and gaseous components. Regarding constant oil temperature, the decrease in the base number of the oil under temperatures lower or higher than 90℃ is larger than that under a temperature of 90℃. The principal causes of degradation are different between cases of the lower and higher temperature tests. It is thought to be caused mainly by the formation of acid with SO{sub}2, NO{sub}2, and water in the lower temperature tests, and by acceleration of nitration and oxidation with NO{sub}2 and oxygen in the higher temperature tests. In addition, the decrease in the base number of the oil was promoted when temperature rises from low to 90℃. We presumed that the acid that mixed to oil under the lower temperature reacted with oil at a 90℃ test condition. From these results, we found that the oil temperature history from the engine start is very important in determining degradation of engine oil.