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 of the wear marks are performed by means of depth-of-field microscope, scanning electron microscope, energy dispersive spectrometer, and other instruments. The experimental data demonstrate that the friction-reduction and anti-wear properties of PAO 6 base oil are enhanced by 22.4% and 56.9% (100 ?), respectively, after the addition of 0.4 wt% nitrogen-doped graphene. Besides, the abrasive and adhesive wear are significantly reduced, which are 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.

Automated summary

In this study, nitrogen-doped element-modified graphene with strong adsorption and superior lubricating properties was prepared using a bottom-up chemical strategy to overcome the limited adsorption capacity of ordinary graphene at high temperature. The reciprocating tribometer was used to simulate the piston operating environment and evaluate the lubrication performance of nitrogen-doped graphene. Characterization and analysis of wear marks were conducted using depth-of-field microscope, scanning electron microscope, energy dispersive spectrometer, and other instruments. The experimental results showed that the friction-reduction and anti-wear properties of PAO 6 base oil were improved by 22.4% and 56.9% (100 ?), respectively, after adding 0.4 wt% nitrogen-doped graphene. Additionally, abrasive and adhesive wear were significantly reduced due to inter-layer slip and superior adsorption performance. The interfacial lubrication mechanism of lubricant protective film under high-temperature conditions was also revealed.