The load-dependent lubrication of the cylinders is performed by a separate cylinder lubrication system. Cylinder lubrication is required in order to lubricate the piston rings to reduce friction between the rings and liner, provide a seal between the rings and the liner, and reduce corrosive wear by neutralizing the acidity of the products of combustion.
The alkalinity of the cylinder lubricating oil should match the sulphur content of the HFO supplied to the engine. If the engine is to be run on low-sulphur fuel oil for a prolonged period, advice must be sought from the cylinder oil supplier and the engine builder as to the most suitable cylinder oil to use.
The ability of an oil to react with an acidic reagent, which indicates the alkalinity, is expressed as TBN. It stands for the Total Base Number. It should correspond to the sulphur percentage of fuel oil to neutralize the acidic effect of combustion.
When high sulphur fuel oil is used for Main engines, a high TBN grade of cylinder oil needs to be used. When the main engine is a “change-over” to Low Sulphur Fuel Oil (LSFO) or Low Sulphur Marine Gas Oil (LSMGO), low TBN cylinder oil needs to be used.
There are two important systems used in modern lubrication systems:
1) Accumulation and Quill System (Wartsila Engines) and
2) Cylinder lubricating units pumping to orifices in the liner (MAN Engines).
The cylinder lubricating oil is pumped from the cylinder oil storage tank to the cylinder oil measuring tank which should contain sufficient LO for two days’ cylinder lubricating oil consumption.
Cylinder lubricating oil is fed to the cylinder lubrication system by gravity from the measuring tank; a heater is located in the gravity line and pipe, and pipes are electrical “trace heated” i.e. the outer surface of the pipe is maintained at a certain temperature.
The heater and trace heating maintains a temperature of 45°C at the lubricating unit. Before starting the Main Engine, it is necessary to pre-lubricate the liners. Pre-lubrication before the start can be made manually or by a sequence in the bridge manoeuvring system.
Watch this video lesson on how cylinder lubrication works: