Engine Oil Degradation Induced by Biodiesel: Effect of Methyl Oleate on the Performance of Zinc Dialkyldithiophosphate

[Image: see text] In the present work, the oxidation stability of blends of methyl oleate, zinc dialkyldithiophosphate (ZDDP), and a high viscosity index mineral base oil was determined by the method of a rotating pressure vessel, while the antiwear abilities were evaluated on a four-ball friction tester. Thereafter, the thermal decomposition characteristics and oxidation products of the oxidized blends were analyzed by a thermogravimetric analyzer and a gas chromatograph coupled to a mass spectrometer, respectively. The results showed that the antioxidation ability of ZDDP was substantially improved by methyl oleate, while the antiwear capacity is markedly impaired by methyl oleate. Furthermore, the thermal decomposition characteristics and oxidation products of ZDDP-containing oils were altered by methyl oleate. The present study evidently convinced that chemical interactions between ZDDP and methyl oleate had occurred, which were attributed to the increased antioxidation ability and decreased antiwear capacity of ZDDP in oils contaminated with methyl oleate.