Improved Scuffing Resistance of Marine Cylinder Oil under High Temperature condition

The recent trend to increase the efficiency and output of large two-stroke diesel engines raises the lubrication severity of the piston ring and the cylinder liner. The temperature of the cylinder liner also tends to increase, keeping the sulfuric acid above its dew point to reduce corrosive wear. One of the most important issues in this context is to prevent severe wear and scuffing under high temperature conditions. The present study was carried out to find out how the scuffing resistance of cylinder oil could be improved using a pin-on-disk type reciprocative sliding test apparatus, in which test conditions of high-speed, high-temperature and oil starvation were similar to those seen in actual diesel engines. It is found that the relationship between scuffing resistance and the total base number (TBN) of the cylinder oil varies greatly depending on the oil feed rate. Under fully flooded lubrication conditions, increasing TBN is effective for improving scuffing resistance. Under oil-starved conditions, however, the usage of high-TBN oils result in low scuffing resistance when compared to low-TBN oils due to the inferior oil film spreading of high-TBN oils. The addition of an oil spreading improver and a heat-resistant dispersant, which enhances oil film spreading under high-temperature conditions, as well as an extreme pressure agent is found to raise the scuffing resistance of high-TBN oils substantially.