Alkalinity:
When fuel burns, the exhaust carries sulphuric acid
which can cause acidic corrosion. For neutralizing this, alkalinity is
used.
Oxidation resistant:
Lube oil is always in contact with air and thus
oxygen presence in oil is inevitable. Moreover, at high temperature of the oil,
the oxidation rate increases. After 85̊ degree C temperature, the
increase in every 10̊ degree C of oil oxidation rates doubles itself leading to
sludge formation, acid production and bearing corrosion. Hence additives are added
to maintain keep these things in check
Load carrying capacity
It
is also one of the important characteristics of lube oil which mainly depends
upon the viscosity of the oil. The load subjected to different internal parts
of the marine engine is very high; hence the load carrying capacity must be
enough to withstand the pressure inside the engine. If this is not achieved
then oil will be forced out and metal to metal contact will result in wiping
out and wear down of the machine.
Thermal conductivity
The
internal parts of marine engine are always in movement producing heat energy.
This heat energy has to be carried away or else it might lead to wear down due
to thermal stresses. The lube oil must cool down the internal parts to avoid
such a situation and must have a good thermal conductivity.
Detergency
Detergency
of the oil is obtained by adding some metallic based additives which will
prevent the buildup of small deposits in the metal surface. In two stroke
engine, the cylinder oil detergency is very important as it removes the
deposits from the ring pack area and keeps the combustion space as clean as
possible.
Disperency
It is the property of the lube oil
which prevents impurities to mix up with itself and keeps them suspended on the
surface. This makes it easy for the separator or clarifier to remove it from
the oil.
High Flash Point
The
flash point is the minimum temperature at which the oil vaporizes to give an
ignitable mixture of air. The flash point should always be on the higher side
so that in case of increase in temperature of the oil, fire hazard can be
avoided. Normally for marine engine lube oils, the flash point is always higher
than 220̊ C.
Low Demulsification Number
It
is not practically impossible to completely avoid contamination of oil with
water. The low demulsification number of the oil helps in easy separation of
water from the oil in the separator or when stored in the settling tank.
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