Condition Monitoring of Lubricating Oil used in Marine Vessels

Abstract

The reliability and efficiency of marine propulsion systems heavily depend on the condition of lubricating oil, which serves as both a protective and functional medium for critical engine components. Over time, lubricating oil undergoes degradation due to thermal stress, oxidative reactions, contamination, and prolonged usage. Traditional oil condition monitoring techniques primarily focus on viscosity changes, spectroscopic analysis, and chemical composition assessments. However, in recent years, polarization current analysis has emerged as a promising diagnostic tool for evaluating the dielectric integrity and degradation behaviour of lubricating oils in marine applications. This study explores the application of polarization current measurement as an effective method for monitoring the deterioration of lubricating oil used in marine vessels. The research involves subjecting lubricating oil samples to controlled thermal aging at varying temperatures (40°C, 50°C, 60°C) over extended periods to simulate real operational stress conditions. By applying a 500 V DC voltage using an insulation tester, the resulting polarization current behaviour is recorded and analyse providing valuable insights into molecular breakdown and insulation capacity loss. Experimental findings indicate that as the thermal aging process progresses, the polarization current exhibits increasing magnitudes, signifying a reduction in the resistivity of the lubricating oil. This behaviour aligns with the formation of conductive degradation byproducts such as free radicals, oxidation compounds and polar contaminants, which alter the dielectric properties of the oil. Notably, samples exposed to higher temperatures (50°C and above) demonstrate significant fluctuations in polarization current, suggesting a higher degree of dielectric instability and lubricant deterioration.