پنجشنبه 7 مرداد 1389
The large bore MAN B&W Model 12K80MC-S 2-stroke engines used by the Cabras
3&4 generation units are an example of large crosshead type engines. In large crosshead
type engines, the cylinder is isolated from the crankcase and a separate cylinder
lubrication system is fitted which supplies a measured quantity of oil to each liner.
The MAN B&W Model 12K80MC-S engine has 12 cylinders each with a cylinder liner.
Each engine cylinder liner has eight lubricating points, where cylinder oil is injected into
the liner via non-return valves from a mechanically driven piston pump lubricator. The
injection of cylinder oil takes place during the engine piston upward stroke. Two-stroke
engines fire-each revolution of the crank-shaft.
Cylinder liners require adequate lubrication in order to reduce piston ring friction and
wear and to neutralize the sulfur in the residual fuel used by the plant. The oil film also
acts as a gas seal between the liner and rings and as a corrosion inhibitor.
Practically all the injected cylinder oil is burned during the cylinder firing. The cylinder
oil is thereby consumed as part of the combustion process that produces electric power.
Therefore, cylinder oil has to be injected at an appropriate rate considering the amount of
sulfur content in the fuel oil and the engine load.
Cylinder oil is a “use once consumable.” It is injected into the cylinder at a feed rate to
give optimum protection against acid corrosion and microsiezure (scuffing). Typical feed
rates for a modern slow speed diesel engine are about 1.3 g/kWh. Note that the cylinder
is the combustion chamber. Therefore, cylinder oil is meant to be burned as part of the
combustion process in the production of electric power.
The oil used to lubricate the piston rings and liner must be thermally stable and be able to
retain an oil film at the high surface temperatures found in the cylinder. The oil must
possess anti wear characteristics, dispersants and detergents to ensure minimum deposits
on the piston and the ring grooves. In addition, because of the high sulfur content in
residual fuel oils, cylinder oil is high alkaline oil with a typical Total Base Number of 70
in order to prevent liner corrosion by sulfuric acid produced by the combustion process.
A specification for typical cylinder oil for an engine burning 3% sulfur fuel is shown
Cylinder Oil ،