Operation
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3. Cylinder Lubricating Oil
A high-alkaline cylinder lubricating oil of the SAE 50 viscosity grade that has a
minimum kinematic viscosity of 18.5 cSt at 100_C is recommended. But, cylinder
lubricating oils of the viscosity grades SAE 40 and SAE 60 can be used in some
conditions. The Base Number (BN) measured in mg KOH/g in accordance with
method ASTM D 2896 shows the alkalinity of the oil.
To set the correct alkalinity of the cylinder lubricating oil, use an on-board monitoring
programme to monitor the piston underside (PU) drain oil. The residual base
number (BN) of the piston underside drain oil shows if the setting values for the
cylinder lubrication are correct. The BN of the cylinder lubricating oils is not an index
for detergency, but a direct measure of alkalinity. The alkalinity of the cylinder
lubricating oil must be set in relation to the sulphur content of the fuel, engine
operation condition and feed rate of the cylinder lubricating oil. The higher the sulphur
content, the higher the BN of the cylinder lubricating oil must be. For a list of validated
cylinder lubricating oils, see paragraph 8.2 Cylinder Lubricating Oils.
When the analysis of the piston underside drain oil shows that the engine operates in
the safe area shown in Fig. 2, you can adjust the feed rate and alkalinity of the
cylinder lubricating oil. The permitted maximum feed rate is 1.2 g/kWh (see 7218−1
Cylinder Lubrication and 7218−3 Feed Rate − Adjustment). If the analysis of the
piston underside drain oil shows that an adjustment to a higher feed rate than
1.2 g/kWh is necessary, you must change to a higher BN cylinder lubricating oil.
3.1 Fuel Sulphur Content and Cylinder Lubricating Oil Base Number
Fig. 1 shows recommendations of applicable cylinder lubricating oils related to the
sulphur content of the used fuel.
If you do not use an on-board monitoring programme to monitor the piston underside
drain oil, use the data given in Fig. 1 to choose an applicable cylinder lubricating oil.
For data about the applicable feed rates, see 7218−1 Cylinder Lubrication and
7218−3 Feed Rate − Adjustment.
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4
3
2
1
Fig. 1: Relation between Fuel Sulphur Content and Cylinder Lubricating Oil BN
2017−08
Lubricating Oils
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