Wartsila ?31DF Series Product Manual page 145

Wärtsilä 31DF Product Guide
9.2.1 Cooling water system for arctic conditions
At low engine loads the combustion air can be below zero degrees Celsius after the compressor
stage, it cools down the cooling water and the engine instead of releasing heat to the cooling
water in the charge air cooler. If the combustion air temperature reaching the cylinders is too
cold, it can cause uneven burning of the fuel in the cylinder and possible misfires. Additionally
overcooling the engine jacket can cause cold corrosion of the cylinder liners or even a stuck
piston.
Thus maintaining nominal charge air receiver and HT-water inlet temperature are important
factors, when designing the cooling water system for arctic conditions. Proper receiver
temperatures must be ensured at all ambient temperatures. If needed, all charge air coolers
can be installed in the LT-circuit. LT-circuit heaters can also be used.
9.2.1.1 The arctic sea water cooling system
In arctic conditions, the hot sea water from the central cooler outlet is typically returned back
to the sea chest in order to prevent ice slush from blocking the sea water filters. An example
flow diagram of the arctic sea water system is shown below.
Fig 9-5
Ships (with ice class) designed for cold sea-water should have provisions for recirculation
back to the sea chest from the central cooler:
● For melting of ice and slush, to avoid clogging of the sea water strainer
● To enhance the temperature control of the LT water, by increasing the seawater temperature
9.2.2 Stand-by circulation pumps (4P03, 4P05)
Stand-by pumps should be of centrifugal type and electrically driven. Required capacities and
delivery pressures are stated in Technical data.
9.2.3 Sea water pump (4P11)
The sea water pumps are always separate from the engine and electrically driven.
The capacity of the pumps is determined by the type of coolers and the amount of heat to be
dissipated.
Significant energy savings can be achieved in most installations with frequency control of the
sea water pumps. Minimum flow velocity (fouling) and maximum sea water temperature (salt
deposits) are however issues to consider.
DBAE248994
Example flow diagram of arctic sea water system
9. Cooling Water System
9-7