choice of base oil
There is more about the composition of lubricating oil in Volume 8 of the However it is sufficient here to say that lubricating oil has several roles Reeds to in protecting the moving components of an engine. It reduces the heat stress by cooling the internal components of the engine and it also protects the components by keeping them apart as they rotate or move in the engine. finally, the oil must keep components dean and free from the effects of combustion which includes neutralizing any acids that may form as a result of the engines operation.
The trunk type engine is more susceptible to the fuel and products of combustion finding their into the crankcase, and contaminating the oil, than is the crosshead type engine Diesel engine lubricating oil should have a detergent additive; these oils sometimes called Heavy Duty. Additives in these oils deter the formation of are deposits on the metal components, by keeping substances, such as carbon particles in suspension. They also counteract the corrosive effect of sulphur compounds, some of the fuels used may be low in sulphur content, in this case the alkaline additive in the lubricating oil could be less.
The lubrication of large two stroke low speed engines is twofold. The crankcase oil will use a straightforward mineral oil , generally with an anti-oxidant and corrosion inhibitor added because the working cylinder is separate from the crankcase and there is less in the way of contaminants from the product of combustion
Due to the crankcase being separate from the underside of the cylinder, no oil is thrown onto the cylinder walls and therefore this type of engine has to have cylinder lubrication which is a total loss system and is separate from the crankcase oil. The requirement for modern tonnage to burn very low sulphur fuel (LSF) in specially designated areas means that the engineers will have to change over to the higher SF as the vessel approaches from its deep sea voyage.
The sulphur content of the fuel has an effect on its lubricity and on its readiness to produce acids when combined with water. Therefore, when the type of fuel is changed over the grade of cylinder oil needs to be changed as well.