Low friction tribofilm formation and distribution on an engine cylinder tested with MoDTC-containing low viscosity engine lubricants

• Published in: Tribology international Vol. 171; p. 107551
• Main Authors: Vaitkunaite, Gerda, Espejo, Cayetano, Thiebaut, Benoît, Neville, Anne, Morina, Ardian
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-07-2022; Elsevier BV
• Subjects: Automotive engines; Chemical composition; Engine cylinders; Friction; Friction reduction; Lamellar structure; Linings; Lubricants; Lubricants & lubrication; Microscopy; MoDTC; Molybdenum disulfide; Passengers; Raman Spectroscopy; Scanning transmission electron microscopy; Spatial distribution; TEM; Tribochemistry; Tribology; Viscosity; Tribochemistry; MoDTC; Raman Spectroscopy; TEM
• ISSN: 0301-679X; 1879-2464
• DOI: 10.1016/j.triboint.2022.107551

The piston-liner tribological contact has a key role in controlling friction caused energy losses in a passenger car engine. This study analyses the MoDTC-containing low viscosity lubricant performance and the resulting low-friction MoS2 tribofilm distribution on the liner surface. The engine liners were tested in a floating liner measurement system, where fully-formulated lubricants with different MoDTC concentrations were utilised to assess the impact of friction modifiers on the friction performance. Tested engine liners were dismantled from the measurement system, and MoS2 tribofilm formation on the liner was quantitatively characterised by Raman Microscopy mapping. The MoS2 tribofilm chemical composition and lamellar structure were further investigated by Transmission Electron Microscopy (TEM), High-Angle Annular Dark-Field Scanning (HAADF) and Energy Dispersive X-ray (STEM-EDX) Microscopy. The findings presented in this paper confirm that MoS2 tribofilm spatial distribution plays a pivotal role in reducing friction in piston-liner contact. 60% friction torque reduction was achieved at BDC area with 0.7% MoDTC concentration in the fully formulated lubricant. Moreover, MoS2 presence in the middle of the liner indicates MoDTC effectiveness throughout the whole engine cycle. Therefore, contributing to the overall energy savings in passenger cars.
•MoS2 tribofilm spatial distribution influences the friction force in the piston-liner tribological contact.•MoS2 tribofilm coverage in the liner is highest at the ring reversal point at the BDC where boundary lubrication is expected.•MoS2 formation was also detected at a narrow location in the middle part of the stroke.•MS2 formation in the middle of the liner could be attributed to the piston secondary motion effect.•MoDTC effect was not observed at the TDC area, regardless of the MoDTC concentration in the lubricant.