Wartsila 31 Product Manual page 100

9. Cooling Water System
9.3.1 Cooling water system for arctic conditions
At low engine loads the combustion air is 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. Depending on the
engine type an additional heater might be needed in the HT-water system as for some engine
types the HT-charge air cooler is replaced with a double-stage cooler on the engine LT-water
cooling water system. For other engine types the HT-water charge air cooler is kept as it is
on a non-arctic package engine. If the setup is with additional HT-heater then the engine
build-on self-sensing thermostatic control valve is removed and replaced with an external
electrically controlled thermostatic control valve.
9.3.1.1 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 in .
Fig 9-9
It is recommended to divide the engines into several circuits in multi-engine installations. One
reason is of course redundancy, but it is also easier to tune the individual flows in a smaller
system. Malfunction due to entrained gases, or loss of cooling water in case of large leaks
can also be limited. In some installations it can be desirable to separate the HT circuit from
the LT circuit with a heat exchanger.
The external system shall be designed so that flows, pressures and temperatures are close
to the nominal values in Technical data and the cooling water is properly de-aerated.
Pipes with galvanized inner surfaces are not allowed in the fresh water cooling system. Some
cooling water additives react with zinc, forming harmful sludge. Zinc also becomes nobler
than iron at elevated temperatures, which causes severe corrosion of engine components.
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
9-12
Example flow diagram of arctic sea water system
Wärtsilä 31 Product Guide
Wärtsilä 31 Product Guide - a1 - 18 October 2016