Any diesel engine will have the following systems which are essentially required:
- Cooling System
- Lubricating oil system
- Fuel Oil System
- Exhaust System
- Starting System.
Let’s straight dive into understanding how cooling system works.
Fresh Water Cooling System:
The cylinder jackets of the engine are cooled by fresh water (sea water is not used since it is corrosive) and the fresh water is cooled in a heat exchanger (F.W. Cooler) by Sea Water.
2 centrifugal pumps (one working and the other standby) are provided fo circulation of water, with a discharge pressure of 3 to 4 bar. The pumps are provided with pressure switches on the discharge side, to sense the pressure. In case of failure of one pump, the pressure switch provided on that pump will activate the starter of the second pump and the second pump automatically gets started.
The fresh water gets heated up as it is circulated in the cylinder jackets and this fresh water is cooled in the heat exchanger (cooler) by sea water (sea water is supplied by main sea water pump). At varying loads on an engine, the temperature of fresh water varies constantly and to maintain a constant temperature around the jackets (to avoid thermal shocks) a bypass system with a thermostatic valve is provided for the heat exchanger. The temperature probe provided on the outlet of the engine senses the outlet temperature and the thermostatic valve controls the water flowing through the heat exchanger depending on the outlet temperature. If the temperature of Fresh Water is dropping due to reduced load, fresh water is bypassed partially so that the outlet fresh water temperature of the engine is always maintained constant.
Normally the fresh water temperature of the engine at an outlet is maintained at 85 – degree celsius for high horsepower engines.
Alarm system is provided in control room to give alarm in case of high temperature (Normally set to 90-degree celsius) and at low pressure of cooling system (about 1.5 bar)
Expansion/Compensation tank: A compensation tank is provided in the system for storing of water for compensating any leakages in the system and also for providing positive suction for centrifugal pumps.
In the next post, we shall look into Lubricating oil system required for a diesel engine.