One of the most reliable internal combustion engines around
is the diesel engine. In many industrial installations, diesel
engines are used as prime movers for the generation of
electricity and for emergency air compressors.
It’s true that they are rugged, but one of the most important
advantages of these engines is the fact that they can be
started by manual cranking. In remote areas, diesel engines
can be counted upon for starting up from scratch.
Once a small diesel engine is started, it can be used to drive
a small electrical generator that can then be used to produce
electrical supply for driving other machines like pumps,
compressors, and for lighting.
How does a diesel engine work?
First there must be combustion of fuel. As we have discussed
in our previous articles, combustion or burning of fuel occurs
whenever there is sufficient heat, fuel and oxygen. When
conditions are just right, combustion can be very rapid. Rapid
combustion causes an explosion in an enclosed area. This is
because of the rapid built-up of hot gases during the process.
In an internal combustion engine like a diesel engine, this
rapid combustion, and built-up of hot gas pressure is used to
push a piston away from the enclosed combustion space.
The piston is attached to a crankshaft through a connecting rod.
Because of this, the engine is able to convert the linear
movement of a piston to a rotating movement of a crankshaft.
The outward movement of the piston turns the crankshaft. However,
the momentum of the turning crankshaft forces the piston back
again towards the engine combustion space in a reciprocating
Once the piston moves away from the combustion space, the
pressure drops. The next stage of operation depends on the
design of the engine. These can be either 2-stroke or 4-stroke
Regardless of the type of design, the spent exhaust gas is
first driven out, and then new fresh air is drawn back into
the combustion chamber.
After this, the rotating crankshaft drives the piston to
compress the fresh air inside the combustion chamber. The
piston acts as a reciprocating compressor at this stage.
The compression of the air causes the latter to become hot – hot
enough to ignite finely distributed fuel particles.
At this moment, fuel is sprayed in at high pressure. The tiny
sprayed fuel particles form a mist inside the combustion chamber.
What do think will happen when you have heat, fuel and oxygen?
A fire! Each tiny particle of the fuel burns rapidly, and an
The cycle starts again, and the crankshaft turns continuously,
the pistons move continuously, and the engine runs.
How does the engine know when to spray fuel, let in air, compress
the air, and exhaust the spent combustion product?
Well folks, start your engines.
Until next time…
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