Application and Classification of Diesel Engine

Diesel engine are widely used as the prime mover for electrical power generating units in the range from 20 KW to 5000 KW. 

About Engine power

The power rating of the diesel engines used to drive electrical generating units are rated in KW or in HP. This is the net horsepower  or Kilowatt delivered on the shaft. K Wm is the mechanical KW. This is the engine HP X 0.746 delivered by the engine to the generator on the shaft. This power does not take into consideration the generator efficiency and losses. K We is the electrical KW. This is the power available at the generator terminals. This is the K Wm minus all the generator losses. These losses are usually the heat losses due to copper 12R, cooling fan losses,...etc.

Engine Classification

Diesel engines used as the prime mover for electrical generating units are classified in different ways. They can be classified in accordance to their ratings, number of strokes, rotational speed and duty type.

Classification according to the power ratings:

There are three international governing standards. Those are SAE, DIN, and JIS. It is a common practice to find several power output ratings for the same diesel engine model. 

Small diesel engines used as the prime movers for electrical generators have three ranges relative to their output power ratings. Small engines range from 20 to 1000 KW. Medium size engines range from 1000 to 2500 KW. Large size engines range exceeds 2500 KW and can reach up to 60000 KW for big bore machines.

Classification according to the number of strokes:

Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost. Two stroke engines are lighter, and cost less to manufacture two stroke engines. The two stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

Classification according to the rotation speed:

In general, the rotation speed is 1500 to 1800 rpm for medium and small size machines. But for large size machines, the low speed range can be as low as 150 to 450 rpm. For medium size machines, the medium speed can be from 600 to 1200 rpm.

Classification according to the service duty:

Service duty is defined  to be how much load is going to be applied on the engine and for how long within a predefined period of time. In general, there are three main service duties: the standby, the prime and continuous duty.