Transient Oil-Film Formation and Asperity-Contact-Controlled Wear in Diesel Engine Bearing Liners During Start–Stop Operation

Diesel engine bearing liners are prone to mixed or local boundary lubrication during start–stop operation because the lubricant film is not fully established during start-up and can collapse during shutdown. This study develops a transient mixed-lubrication wear model coupling oil-film pressure, asperity contact, journal motion, and wear, and validates it using component-level start–stop tests on full-size bearing-liner specimens with the Archard wear coefficient taken as a nominal engineering value of k = 5 × 10−6 mm3∙N−1m−1 for the soft electroplated PbSn18Cu2 bearing-liner surface—it is not calibrated against the present wear measurements. The results show that wear accumulates mainly during the early start-up stage, while shutdown contributes relatively little. Wear severity is governed less by the maximum oil-film pressure than by the duration and intensity of asperity contact during the initial film formation. Under a load of approximately 9 kilonewtons (kN), repeated cycles between 0 and 600 revolutions per minute (rpm), and controlled reservoir oil temperatures of 30–90 °C, the measured wear loss decreases from 4.6 mg at 30 °C to 1.6 mg at 90 °C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) (Philips, Eindhoven, The Netherlands) show more pronounced ploughing grooves, adhesive transfer, plastic deformation, and local spalling at lower reservoir oil temperature. These results indicate that under the present conditions, a higher reservoir oil temperature improves lubricant supply, reduces asperity-contact accumulation, and mitigates start–stop wear. The structural state and elemental composition of the contact zone are also modified by asperity interaction and are treated as a coupled factor in the interpretation of these results.