Diesel plant lubrication and cooling systems

Need of lubricating system

Lubrication puts a thin oil film between moving surfaces of the engine. It is needed to:

• reduce friction and wear between piston, rings, liners, bearings and gears;
• carry away heat from pistons and bearings (cooling action);
• seal the gap between piston rings and liner, so compression and power are not lost;
• clean the parts by carrying away carbon and metal particles to the filter;
• prevent corrosion and reduce noise.

Without lubrication the parts would overheat and seize in a few minutes.

Cooling systems of a diesel power plant

About 25–35 % of fuel heat goes to the cylinder walls. If not removed, the lubricating oil breaks down, pistons seize and valves warp. The main methods are given below.

1. Open (once-through) cooling system

 River/well -> pump -> filter -> engine jacket
                                    |
           river (downstream) <-----+ hot water

Water is taken from a natural source, passed through the jacket once and discharged. Simple and cheap, but needs plenty of clean water; scaling from impurities.

2. Closed (recirculating) cooling system - used in most plants.

  +-> engine jacket -> hot water -> heat exchanger -+
  |                                  (soft water)   |
  +---- pump <---- expansion tank <-----------------+
               raw water side:
  cooling tower/pond -> pump -> HX -> tower (spray)

Soft (treated) water circulates in a closed loop through the engine jacket and a heat exchanger. The heat exchanger is cooled by raw water from a cooling tower or spray pond (or by air in a radiator for small sets). No scaling in the jacket, little water loss, so it is preferred.

3. Air cooling (small engines only): fins on the cylinder and a fan blow air over them. Simple, but cooling is not uniform and suits only small sets.