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Analysis of the modern oil viscosity changes during their operation in combustion engines

Młynarczak A., Sikora G.

Journal of KONES

2014

Vol. 21, No. 4

361--368

During normal operation, oxidation products gradually foul lubricating oil and external contaminants like fuel, water, sulphur compounds and friction nodes wearing products. As a result, lubricating oil changes its properties, among other things viscosity. In normal service conditions of marine diesel engines lubricating oil viscosity increases due to vaporizing of lube oil light ends during operation in high-temperature areas and oxidation process. Quantity of organic particulates accumulated in lubricating oil increases as a result of oxidation process. Oxidation products have bigger than lubricating oil molecular weight. So as to prevent oxidation process-lubricating oils are provided with antioxidant additives. On the other hand mechanical breakdown of high molecular substances in diesel engine bearings and gas oil leakages cause lubricating oil viscosity drop. The test results presented in the paper show that the lubricating oil viscosity during its operation in the internal combustion engines decreases. The value of viscosity decrease depends mainly on the motor's technical condition, the amount of oil in lube oil system, mode of ignition and its operation. Viscosity tests were performed for the lubricating systems of different engines on a Haake III Mars rheometer at 90 􀃛C for variable shear rates. Additionally, in order to determine engine condition, the detail analysis of the tested oil chemical content has been made oil using Spectrol Q100 spectrometer. In the most cases, the research results indicate lubricating oils viscosity decrease and it is possible to determine the relationship between the dynamic viscosity changes and shear rates for the particular engines. In authors opinion the viscosity drop of the tested modern lubricating oils may be caused by better antioxidant additives, which effectively moderate or even prevent the oxidation process. Lubricating oils viscosity drop is dangerous phenomena due to the lowering of the bearings capacity force and possibility of boundary friction.