Rheological behaviour of lubrication oils used in two-stroke marine engines

The purpose of this study is to investigate the rheological behaviour of commercial lubrication oils used for cylinder lubrication in two-stroke marine diesel engines. Furthermore, it is of interest to investigate whether the viscosity of lubrication oils is affected by different levels of alkalinity.

Viscosity measurements are performed using both rotational and capillary rheometry. It was possible to measure oil viscosity in the shear rate from 0.1 to 3,000 s⁻¹ using rotational rheometry, whereas capillary rheometry allowed measurements in higher shear rates from 5 × 10⁵ to 1.3 × 10⁶ s⁻¹ at 50°C.

The viscosity measurements show that the studied lubrication oils behave as a Newtonian fluid and that the viscosities are insensitive to the level of alkalinity. Furthermore, the viscosity/temperature dependency for the lubrication oils was found to fit the Arrhenius model.

This study presents useful information about the rheological behaviour of lubrication oils, more precisely how the oil properties are affected by shear rate, temperature and level of alkalinity. The value of this research is considered to be important for designing two-stroke diesel engines and cylinder lubrication systems.