Abstract: In order to investigate the effect of detergent on the performance of base oil containing zinc dialkyldithiophosphate(ZDDP) and molybdenum dithiocarbamate(MoDTC) as anti-wear and anti-friction agents, overbased synthetic calcium sulfonate(T106D)，overbased synthetic Magnesium sulfonate(T107), or alkylphenolate calcium sulfide (T115B) was added to the base oil containing composite ZDDP/MoDTC, respectively. The crankcase simulation test and four-ball machine wear resistance test were carried out. The high magnification scanning electron microscope(SEM) was used to characterize the surface morphology of steel ball after test. The results showed that the longer the crankcase simulation test time, the more obvious the difference in the base oil coking inhibition, and the addition of 3 detergents at the same time had the best detergency for the base oil with composite ZDDP/MoDTC. The base oil containing T107 had a lower coking tendency. The anti-wear test using the four-ball machine after the crankcase simulation test showed that the three detergents had little effect on the anti-wear performance of the base oil containing ZDDP/MoDTC compound. The main reason for the change in anti-wear performance was the decrease in the stability of MoDTC after high temperature. SEM results of the surface morphology of the steel ball showed that detergent would weaken the recovery effect of ZDDP/MoDTC compound base oil on the friction surface.

Key words: ZDDP, MoDTC, base oil, detergent, wear scar diamter