A major problem in lubricated piston ring/cylinder liner contact sliding systems is the tribological failure mechanisms known as scuffing. In order to evaluate and better understand this damage phenomenon in these tribological systems, a tilted linear tribometer (TE77) for application-oriented reciprocating model tests was developed and validated with scuffed field engine parts. With precise oil lubrication, original engine parts, such as CKS-coated piston rings (chromium-based coating with included aluminum oxides), original liners and fully formulated lubrications, were tested under conditions similar to the most critical part of the internal combustion engines (ICEs), known as fired top dead center (FTDC). Various in situ measurements during the tests allowed for a detailed investigation of the damage processes (crack transformation) on the tribological components. For the coated piston ring, vertical cracks were attributed to residual stresses, while horizontal cracks resulted from shear stresses. The crack transformation and wear results from other studies were confirmed for the liner. The results from FIB (Focused Ion Beam) cuts, along with EDS and SEM analyses, revealed that Fe (deriving from material transfer) acts as a catalyst on the CKS layer for the tribopads and that zinc sulfides are not present everywhere.

This study compares the tribological performance, thermal stability, and damage evolution of piston rings with chromium–aluminium oxide ceramic (C1), chromium–microdiamond (C2), and chromium nitride (C3) coatings on cast iron (S1), cast steel (S2), and stainless steel (S3) substrates under simulated fired top dead centre conditions. A TE77 linear tribometer and original engine components were used with quasi-continuous lubrication (TS1) and discontinuous lubrication (TS2) to determine seizure limits, temperature responses, friction, and damage progression. C3/S3 achieved the highest mean seizure limit under TS1 (16.7 MPa), whereas C2/S2 performed best under TS2 (21.5 MPa). Near-surface measurements indicated system-dependent near-surface temperature responses: S1 systems exhibited higher piston-ring temperatures and lower contact-near liner temperatures than S2 systems, together with slightly lower coefficients of friction. Thermal cycling and controlled-stop tests showed earlier crack formation for C1, delayed cracking for C2, and no visible cracking for C3/S3 under the tested conditions. By expanding the previously investigated single reference system to five industrial coating–substrate combinations and introducing a discontinuous lubrication scenario, this study provides new comparative evidence of system-dependent seizure resistance, thermal response, and damage evolution.

Reducing friction in the piston ring–cylinder liner contact is a key area for improving the efficiency of internal combustion engines. While tribological studies commonly focus on the top dead centre region using linear tribometers, the mid-stroke regime—with its higher sliding velocities—remains experimentally inaccessible to most conventional test methods. This study presents a rotating ring-on-liner tribometer that enables investigations at constant relative speed by transitioning the motion from oscillating to rotating. A cylindrical substitution geometry for the piston ring specimen is derived through a coupled elastohydrodynamic and asperity contact simulation approach to reproduce realistic load-sharing behaviour. Experimental results from starved lubrication tests demonstrate stable contact conditions with a low coefficient of variation in wear, confirming good reproducibility. Stepwise performed Stribeck tests at 40 °C and 100 °C reveal characteristic friction–velocity behaviour, including the transition from mixed to hydrodynamic lubrication. Although the test rig’s maximum sliding speed and steady-state thermal conditions differ from fired engine environments, the methodology closes an important gap between low-speed linear tribometers and complex floating-liner systems. The presented approach provides a flexible and robust platform for controlled parametric studies of ring-on-liner contacts under application-relevant lubrication regimes.