Tribological evaluation of few-layer nitrogen-doped graphene as an efficient lubricant additive on engine cylinder liner: Experiment and mechanism investigation

The restricted adsorption capacity of ordinary graphene at high temperature limits its application in engine lubrication. To address this, nitrogen-doped element-modified graphene with strong adsorption and superior lubricating properties is prepared by a bottom-up chemical strategy in this study. The reciprocating tribometer is aimed at simulating the piston operating environment to determine the lubrication performance of nitrogen-doped graphene. The characterization and analysis for the wear marks are performed by means of depth-of-field microscope, scanning electron microscope, energy dispersive spectrometer and other instruments. The experimental data demonstrates that the friction-reduction and anti-wear properties of PAO 6 base oil are enhanced by 22.4% and 56.9% (100 °C), respectively, after the addition of 0.4 wt% nitrogen-doped graphene. Besides, the abrasive and adhesive wear are significantly reduced, which is attributed to its inter-layer slip along the sliding direction and superior adsorption performance. Finally, the interfacial lubrication mechanism of lubricant protective film under high temperature conditions is revealed.