N-Oleoyl Sarcosine as an Engine Oil Friction Modifier, Part 1: Tribological Performance of NOS+ZDDP Mixture at 100°C

The friction coefficient when a Fe surface was lubricated with an additive mixture of N-Oleoyl sarcosine (NOS), a commercial organic friction modifier, and zinc dialkyldithiophosphate (ZDDP) was measured at 100°C using a ball-on-disk tribometer under boundary lubrication conditions. The sliding surface was observed with a 3D laser microscope to investigate the tribo-film morphology and to evaluate the anti-wear performance. The findings indicate that this additive mixture enhanced tribological lubrication behavior in terms of friction-reducing and anti-wear properties under extended sliding cycle conditions. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) studies were conducted to analyze the elemental composition of sliding surfaces after tribo-tests and to estimate the friction reduction mechanism of the additive mixture. The EDX results revealed a noticeable decrease in S, suggesting that the NOS suppresses ZDDP decomposition and reduces the adsorption of the decomposition products.