Diesel engine is the prime mover, which drives an alternator to
produce electrical energy. In
the diesel engine, air is drawn into the cylinder and is
compressed to a high ratio (14:1 to 25:1). During this compression, the air is
heated to a temperature of 700–900°C. A metered quantity of diesel fuel is then
injected into the cylinder, which ignites spontaneously because of the high
temperature. Hence, the diesel engine is also known as compression ignition
(CI) engine.
DG set can be classified according to cycle type as: two-stroke
and four stroke. However, the bulk of IC engines use the four stroke cycle. Let
us look at the principle of operation of the
four-stroke diesel engine.
Four Stroke - Diesel Engine
The 4 stroke operations in a diesel engine are: induction stroke,
compression stroke, ignition
and power stroke and exhaust stroke.
1st : Induction stroke - while the inlet valve is open, the descending
piston draws in
fresh air.
2nd : Compression stroke - while the valves are closed, the air is
compressed to a pressure of
up to 25 bar.
3rd : Ignition and power stroke - fuel is injected, while the valves are
closed (fuel injection
actually starts at the end of the previous stroke), the fuel
ignites spontaneously and
the piston is forced downwards by the combustion gases.
4th : Exhaust stroke - the exhaust valve is open, and the rising piston
discharges the spent
gases
from the cylinder. Detail Click
Fig: Schematic Diagram of Four-Stroke Diesel Engine
Fig: DG Set System
