Analysis of Tribological Performance of Functionalized Carbon Nanotube-Reinforced Lubricants in Journal Bearings

Reducing friction in radial journal bearings has a direct effect on energy consumption and component service life. This study examined the tribological behavior of a hydrodynamic journal bearing lubricated with Shell Helix Ultra 5W-40 synthetic motor oil blended with functionalized multi-walled carbon nanotubes (FMWCNTs) at mass fractions ranging from 0.01 to 0.5 wt%. The nano-lubricants were prepared through mechanical stirring followed by ultrasonication, using Triton X-100 as a surfactant, and they were subsequently characterized by Field Emission Scanning Electron Microscope, FT-IR Spectrometer, Ultraviolet-Visible spectroscopy spectroscopy, and zeta potential measurements. Tests were carried out at loads of 50–500 N, rotational speeds of 0–1500 rpm, and bearing clearances of 0.12–0.28 mm. Stribeck curves were generated to evaluate how FMWCNT concentration influenced the friction coefficient (μ) and the transitions between lubrication regimes. The results show that the effect of adding FMWCNTs on friction depends on both concentration and operating conditions. At 0.01 wt%, friction performance was comparable to or better than that of the base oil. At concentrations of 0.05 wt% and above, the friction coefficient increased noticeably. These findings indicate that selecting an appropriate FMWCNT concentration and maintaining stable dispersion are the key factors governing the performance of FMWCNT-reinforced lubricants.