A Study of Lead Corrosion of Diesel Engine Oil

The effect of base oils, sulfur-containing multi-functional additives and dispersants in formulated diesel lubricants on lead corrosion was evaluated by a self-established high temperature corrosion bench test. Test lead coupons were analyzed by XPS to determine the resulting surface chemistry. The results showed a close correlation between the oxidation stability of base oil blend and the lead corrosion of formulated diesel lubricants. The zinc dialkyldithiophosphate (ZDDP) and zinc dialkyldithiophosphate (ZDDC) have formed different protective films on lead coupon surfaces. A more or less amount of the protective film formed is the main factor affecting the degree of lead corrosion. The glassy zinc phosphates protective film formed by ZDDP is more effective than the zinc sulfides film formed by ZDDC. The interaction between dispersants and ZDDP had a significant impact on lead corrosion.