Effect of Aged Oils on Ring-Liner Wear

With the trends to increase drain oil interval to reduce the cost of ownership of Heavy-Duty vehicles and to use low ash oils to mitigate degradation of Diesel Particulate Filter performance, the efficiency of lubricant additive s, especially the antiwear ones, are of great interest. However, most of the tribological tests are still done with fresh oils or, in a few cases, with artificially aged oils. In this work, the piston ring and cylinder liner were rig tested for friction and wear on a short reciprocating tester with two oils: a fully formulated SAE 10W-40 API CI-4/ACEA E7 and a sample of the same oil after 500 h of an engine test. Friction was measured along with the rig test, and liner wear was evaluated after test by different parameters based on the bearing curve of roughness. Compared with the fresh oil, the aged oil showed slightly lower friction, but significantly higher liner wear. After the test, the wear track of cylinder liners was also analyzed by Energy Dispersive X-ray Spectrometry (EDS) and compared with analyses of the parts before the test. More Zinc (Zn) and Phosphorus (P) were found on the wear track of the liners tested with the fresh oil. The fresh oil formed more zinc dialkyl dithiophosphate (ZDDP)-derived tribofilms that mitigated liner wear but increased friction. Samples of a liner with accumulated 500 engine hours were also tested with the aged oil and presented intermediate values of friction, wear, and ZDDP tribofilm elements.