Tribological Effects of BN and MoS₂ Nanoparticles Added to Polyalphaolefin Oil in Piston Skirt/Cylinder Liner Tests

We report in this article the friction and wear results of polyalphaolefin (PAO 10) base oil with the addition of 3 wt% boron nitride (BN) and molybdenum disulfide (MoS₂) nanoparticles with nominal size of 70 and 50 nm, respectively. The formulations were tested using cast iron cylinder liner segments reciprocating against aluminum alloy piston skirt segments at 20, 40, and 100 °C. The results showed that, at a load of 250 N and a reciprocating frequency of 2 Hz, BN did not lower friction whereas MoS₂ nanoparticles were very effective at reducing both friction and wear, compared with the base oil. The viscosities of both formulations were similar to the base oil, which allowed for a direct comparison between them. Raman spectroscopy showed the formation of an aligned MoS₂ layer on the cast iron liner surface, which most likely functions as a tribofilm. In the case of the cast iron liner tested with BN nanolubricant, no traces of BN were found. The effect of surfactants was also studied, and it was found that some surfactants were not only beneficial in dispersing the nanoparticles in oil, but also in producing some reduction in friction and wear, even when used as stand-alone additives in PAO 10.