Cooling system
The main function of the engine cooling system is to cool the metal adjacent to the combustion chamber. But during the operation cooling is also necessary to cool scavenging air, lubricating oil, exhaust manifold, crosshead guides, etc. The cooling media used in cooling are fresh and sea water, lubricating oil and scavenging air.
The cooling system which is used more often is the closed circuit system consisting of a primary (fresh water) circuit and a secondary (sea water) circuit. In this case sea water is used for cooling fresh water, oil and scavenging air.
The water enters the bottom of each cylinder jacket, then it flows upward, passes into the cylinder head, the exhaust valve cage, exhaust manifold jacket and after that it gets into the thermostat. This temperature regulator delivers part of the water to the cooler and the rest of it to the circulating pump to be recirculated.
The pistons are usually cooled with fresh water or oil. If the pistons are cooled with water the piston cooling system is separate from the jacket system. Cooling the pistons with oil eliminates troubles due to leakage of water into the lubricating oil. In both cases sea water is used only in coolers, through which the fresh water and oil pass leaving the engine.
The use of fresh water (as cooling medium) reduces scale formation, corrosion. And besides it is possible to keep (maintain) correct temperature of cooling water.
Lubricating Oil System
Correct lubrication of any diesel engine is necessary for proper operation, because the supply of lubricating oil serves the following purposes.
Lubrication of bearings, cylinders, piston rings and other moving parts of the engine.
Neutralization of the acids that are formed during the combustion and corrosion reduction of cylinders, pistons and piston rings.
Cooling of bearings and pistons.
Keeping the inside of the engine clean.
Transport of impurities such as dust, rust, water, combustion products etc away from the engine to filters and separators.
Lubricating oil used in the engines is a mixture of a base oil that has a lubricating and cooling effect, and lubricating oil additives (which must be capable of neutralizing any acid and carrying away impurities).
During operation, the lubricating oil in the engine is slowly polluted by small particles from the combustion in the cylinders and ingress of water that is why the lubricating oil should be cleaned continuously. Small particles are removed by filtering and big ones by separating.
The lubricating oil system comprises some units and devices. A pump sucks oil from a lubricating oil drain or bottom tank. To safeguard the pump, a coarse filter is installed between the pump and the bottom tank. The pump forces the oil through a lubricating oil cooler and filters to the main engine where the oil is distributed to bearings and pistons.
The pressure oil pipe on the engine can be divided into two branches: a lubricating oil branch and a cooling oil branch. The lubricating oil runs from the bearings into the crankcase, from there to the engine oil pan, and finally through a sieve in the oil pan to the lubricating oil bottom tank from where it is sucked up again by the lubricating oil pump.
The oil that was used for cooling the pistons flows to the separator fist and then back to the lubricating oil bottom tank.