Piston ring and cylinder liner wear aggravation caused by transition to greener ship transports–Comparison of samples from test rig and field

New and upcoming emission regulations for ships will push towards greener sea based transports. Changing the fuel, from heavy fuel oil to natural gas, is a promising approach to fulfil these regulations, but tribological problems are expected to appear when the sulphur-free gas replaces the sulphur-rich heavy fuel oil. The aim of this study was to investigate the role of sulphur for the high performance of current tribosystem in the cylinder. Field worn samples were examined and no tribofilm containing sulphur was detected, but grain refinement and plastic deformation was found below the sliding surfaces. A reciprocating test rig was used in order to simulate the tribological conditions for the piston rings and cylinder liner. Tests were run with fresh cylinder oil as well as with used cylinder oil, where the latter was used in order to simulate the chemical environment in the cylinder of an engine. Tribofilms were formed on the surfaces during these tests, and the tribofilms formed on samples run with used cylinder oil contained more sulphur than tribofilms formed on samples run with fresh cylinder oil. So far, we have not been able to see any beneficial effects of higher sulphur content in the oil.