This study aimed to develop an experimental method for producing artificially aged oil with properties—such as coefficient of friction, average wear scar diameter, and antiwear additive content—similar to those of used oil contaminated with alternative fuel, sampled after 129 h of engine test bench operation. A design of experiment (DoE) methodology was applied to examine the effects of various parameters and identify optimal settings. Friction and wear tests were conducted using an Optimol SRV5 tribometer in a ball-on-disc configuration, while wear scars were analyzed with a Keyence VHX-1000 digital microscope. Oil analysis was conducted with an Anton Paar 3001 viscometer and a Bruker Invenio-S Fourier-transform infrared spectrometer. The DoE results showed that the heating duration had a negligible effect on oil degradation. Aging time primarily affected changes in the friction coefficient and average wear scar diameter, whereas aging temperature was the primary factor influencing the anti-wear additive content. Gaussian elimination identified the optimal aging parameters as 132.8 °C and 103.1 h. These results were confirmed through surface analysis using a ThermoFisher NexsaG2 X-ray photoelectron spectrometer, which showed that the tribofilm composition of the used oil most closely matched that of artificially aged oils prepared at 120 °C for 96 h and 140 °C for 120 h. The strong correlation between the predicted and experimentally confirmed conditions demonstrates the reliability of the proposed method for replicating realistic aging effects in lubricating oils.
Pintér et al. (Thu,) studied this question.