On Wärtsilä 4-stroke engines the main purpose of the cooling system is to remove
the heat from the engine generated in the combustion process. In addition, the
cooling system maintains the charge air and lubricating oil temperatures at nominal
values. A secondary function for the system is to preheat the engine block during
operating breaks. /16/; /22/
Indirect cooling is used on Wärtsilä 4-stroke engines, meaning that the heat is released
to a closed coolant circuit instead of releasing the heat directly to cooling
air without using a cooling agent /30, p. 309/. In the cooling system the cooling
water is circulated through the heat sources of the engine. The heat is conducted to
the cooling water and the circulating motion carries the heat away from the heat
sources. The cooling system also includes a method to remove the heat load from
the operating cycle to the environment. For example radiators, cooling towers,
central coolers and box coolers are used for this purpose. /16/; /22/
In most cases the cooling system consists of two separate cycles that are referred
to as primary cycle and secondary cycle. The primary cycle is always a closed cycle
that circulates the cooling water in the heat sources and is cooled down by a
heat exchanger. Treated fresh water is used in all Wärtsilä 4-stroke engines as a
cooling agent on primary cycle and glycol is used as an additive to prevent freezing
when operating in cold conditions. The heat exchanger in the primary cycle
serves as a connection for the heat to transfer to the secondary cycle which then
takes care of the heat disposal. There are also applications where the heat exchanger
in the primary cycle serves directly as a heat exposal method, e.g. when