Page 44 - Introduction to Marine Engineering
P. 44
Diesel engines 31
Se» water in
Figure 2.18 Fresh water cooling system
The cylinder jacket cooling water after leaving the engine passes to a
sea-water-circulated cooler and then into the jacket-water circulating
pumps. It is then pumped around the cylinder jackets, cylinder heads
and turbo-blowers. A header tank allows for expansion and water
make-up in the system. Vents are led from the engine to the header tank
for the release of air from the cooling water. A heater in the circuit
facilitates warming of the engine prior to starting by circulating hot
water.
The piston cooling system employs similar components, except that a
drain tank is used instead of a header tank and the vents are then led to
high points in the machinery space. A separate piston cooling system is
used to limit any contamination from piston cooling glands to the piston
cooling system only.
Sea water cooling system
The various cooling liquids which circulate the engine are themselves
cooled by sea water. The usual arrangement uses individual coolers for
lubricating oil, jacket water, and the piston cooling system, each cooler
being circulated by sea water. Some modern ships use what is known as a
'central cooling system' with only one large sea-water-circulated cooler.
This cools a supply of fresh water, which then circulates to the
