Study of the Effects on Plain Bearings in Simulated Corrosion Tests Using Carbon neutral Fuels

Many countries around the world are currently working toward carbon neutrality, which would reduce greenhouse gas emissions to net zero by 2050. As part of our efforts to achieve carbon neutrality, we have developed low friction bearings that contribute to reduced fuel consumption, and high load capacity bearings for increased engine output and longer service life. Meanwhile, Countries around the world are also considering engines that use carbon-neutral (CN) fuels, such as hydrogen and e-fuel, as part of their efforts to achieve carbon neutrality. It was reported that CN fuels differ significantly from gasoline and diesel in the chemical composition of gases produced after combustion. In particular, hydrogen-fueled internal combustion engines generate more water during combustion than gasoline engines, and nitrogen oxides emissions (NOx) have also been observed under some combustion conditions. Dissolution of these substances in engine oil is expected to create a corrosive environment for sliding bearings, leading to reduced performance. In addition to properties such as low friction and wear resistance, which are required for sliding bearings, chemical stability is considered to become more important. In this study, the effects on sliding bearings were confirmed in corrosion tests simulating a CN-fueled combustion engine environment. During the tests, market-proven sliding bearings for gasoline engines were tested immersed in engine oil blended with nitric acid and water based on information from the engine manufacturer. The results revealed that the corrosion susceptibility of bismuth-based materials was significantly higher in acid-containing oil. On the other hand, no corrosion was observed for polymer-based materials. In addition to hydrogen, simulated corrosion tests for e-fuel and bioethanol were also conducted and reported in this study. Accumulation of data from these tests will help clarify the criteria for selecting sliding bearing materials and improve the reliability of engines.