WÄRTSILÄ VASA 6L32, Instruction Manual

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BN 30 oils are also a recommended alternative when operating on crude oil having low
sulphur content. Though crude oils many times have low sulphur content, they can contain
other acid compounds and thus an adequate alkali reserve is important. With crude oils
having higher sulphur content BN 40 – 55 lubricating oils should be used.
If both distillate fuel and residual fuel are used periodically as fuel, lubricating oil quality has
to be chosen according to instructions being valid for residual fuel operation, i.e. BN 30 is
the minimum. Optimum BN in this kind of operation depends on the length of operating
periods on both fuel qualities as well as of sulphur content of fuels in question. Thus in
particular cases BN 40 or even higher BN lubricating oils should be used.
The intervals between lubricating oil changes may be extended by adding oil daily to keep
the oil level constantly close to the maximum level.
An example of BN depletion curve with different BN lubricating oils is shown below.
Additives
The oils should contain additives that give good oxidation stability, corrosion protection,
load carrying capacity, neutralisation of acid combustion and oxidation residues and should
prevent deposit formation on internal engine parts (piston cooling gallery, piston ring zone
and bearing surfaces in particular).
Foaming characteristics
Fresh lubricating oil should meet the following limits for foaming tendency and stability,
according to the ASTM D 892-92 test method:
Sequence I:
100/0 ml
Sequence II: 100/0 ml
Sequence III: 100/0 ml
-20
0
20
40
60
0 2000 4000 6000 8000 10000
SERVICE HOURS
BN 55 Oil BN 40 Oil BN 30 Oil
Oil Volume: 0.6 l/kW (Wet Sump)
Fuel sulphur content: 2.5 w-%
BN Condening limit: 20 mg KOH/g