A new tribology test procedure to investigate ethanol dilution on engine oils 2018-36-0090

With the worldwide trend towards CO2 emission reduction, renewable fuels such as ethanol are gaining further importance. However, the use of ethanol as a fuel can bring some tribological impacts. Friction and wear of engine parts when lubricants are contaminated with ethanol are not very well understood. Within this scenario, the present paper introduces a new procedure to investigate the ethanol dilution on the performance of engine oils. Friction and wear of actual piston ring and liner were evaluated in a reciprocating test designed to emulate real thermomechanical conditions of both urban and highway car use. In addition to fresh oil, lubricant/ethanol emulsions were prepared carefully following two different procedures - unheated and heated mixing. The former to emulate cold start and “bakery” driving use, the latter to reproduce what happens after the engine heats in normal conditions. Thus, four contamination recipes: ethanol and water-ethanol, unheated and heated mixing prior the test were compared to the fresh oil. Confirming literature outcomes from previous works, the contaminated oils showed lower friction than the baseline oil. Firstly, when tested at 50°C, the presence of both contaminants reduced ring/liner friction by about 15%. However, at 130°C, ethanol effect was mitigated, probably due to its rapid evaporation. In contrast, water-ethanol containing oil kept a level of 8% in friction reduction even at high temperature, when compared to its fresh version. The wear of cylinder liner and piston ring were not significantly affected by the dilutions, but somehow surprisingly liner wear was slight lower for the tests with contaminated oils.