Tribological Evaluation of Few-Layer Nitrogen-Doped Graphene as an Efficient Lubricant Additive on Engine Cylinder Liner: Experiment and Mechanism Investigation
Wenwu Lei, Wentao Tang, Xiaoyu Mo, Zhiqun Tian, Pei Kang Shen, Tiancheng Ouyang
Abstract
Abstract 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 °C), 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.