Cylinder lubrication
Cylinder oil is pumped from Cylinder Oil Storage Tank to the Cylinder Oil Service Tank, placed
min. 3000mm above the cylinder lubricators. The cylinder lubricators are mounted on the roller
guide housing and are interconnected with drive shafts. Each cylinder liner has a number of
lubricating orifices, through which the cylinder oil is introduced into the cylinders via non-return
valves.
Large slow-speed diesel engines are provided with a separate lubrication system for the cylinder
liners. Oil is injected between the liner and the piston by mechanical lubricators which supply
their individual cylinder, A special type of oil is used which is not recovered. As well as
lubricating, it assists in forming a gas seal and contains additives (For improve or preserve)
which clean the cylinder liner.
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, to provide a seal between the rings and the liner, and to 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 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, 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.
The following criteria determine the control:
• The cylinder oil dosage must be proportional to the Sulphur content of the fuel
• The cylinder oil dosage must be proportional to the engine load, ie, the cylinder fuel
supply.
The quantity of cylinder oil injected at the individual injection points is controlled by the
cylinder lubrication control system. Each cylinder LO injector (quill) is effectively a non-return
valve which is opened by the pressure oil directed to it by the lubricator control system. Cylinder
oil feed rates can be adjusted, but adjustments must only be made by authorized personnel
only.
Lubricating Oil Sump Level
The level of lubricating oil indicated in the sump when the main engine is running must be
sufficient to prevent vortexing (a powerful circular) and ingress of air which can lead to bearing
damage.
The sump level is to be maintained according to manufacturer’s/shipbuilder’s instructions. The
‘Sump Quantity’ is always at the same safe operating level and is given in liters. It is essential
that the figures are mathematically steady and correct from month-to-month, considering
consumption, losses and refills and reported.
The ‘Sump Quantity’ is calculated with the engine stopped, but the lubricating oil pump in
operation, thus keeping the system oil in circulation.
Sufficient reserve quantities of lubricating oil must always be held, i.e. to completely fill the
main sump and sufficient quantities of other lubes must be held to cover the intended voyage
plus 20%. Lubricating oils are a major expenditure item; therefore, all purchasing must be per-
planned with the aim of buying the maximum amounts from the cheapest supply sources which
are primarily the US, Europe and Singapore. Lube oil requisitions should be sent to the office at
least 10 days before the intended port of purchase and clearly indicate if the vessel requires
supply in bulk or in drums.
Pre-Lubrication Pumps
They provide an essential part of the lubrication system on many types of engines in particular
auxiliary engines with engine driven lubricating oil pumps.
They provide a supply of oil to the bearings prior to start up and limit the length of time that
boundary lubrication exists and shorten the time when hydrodynamic lubrication commences.
They must be maintained and operated in accordance with the manufacturers’ instructions.
Hydrodynamic lubrication is the term given when a shaft rotating in a bearing is supported by a
layer or wedge of oil so that the shaft is not in contact with the bearing material.
Overview of a Marine Diesel Engine Piston
The main diesel engine piston is made up of two parts; the crown and the skirt. The crown is
subjected to the high combustion temperatures, so it is cast from an alloy of steel, chrome and
molybdenum. The crown has cooling passages cast into it, through which the cooling water
passes. The crown is bolted through the cast iron skirt into the forged piston rod using long,
high tensile, studs; the nuts being tightened using hydraulic tensioning gear.
The head of the crown can sometimes be coated with Inconel (nickel containing chromium and
iron) ; a hard, high temperature alloy, to prevent erosion from the burning of heavy fuel oil.
