高温下におけるシリンダ油の耐スカッフィング性向上に関する研究

Abstract

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 sulphuric 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 scuffing resistance of the cylinder oil could be improved using a pin-on-disk type reciprocative sliding test equipment, in which test conditions of high speed, high temperature and oil starvation were similar to those seen in large diesel engines. The relationship between scuffing resistance and total base number (TBN) of the cylinder oil varies greatly depending on the oil feed rate. Under fully flooded lubrication condition, increasing total base number of the cylinder oil is effective in improving scuffing resistance. Under oil starved lubrication condition, however, the usage of high TBN oil results in low scuffing resistance when compared to low TBN oil because of the inferior oil film spreading of high TBN oil. The usage of an oil spreading improver and a heat resisting dispersant, both which enhance oil film spreading under high temperature condition, as well as an extreme pressure agent was found to raise the scuffing resistance of high TBN oil.