an internal combustion engine transforms
the chemical energy and fuel to
mechanical energy
diesel engines which have been serving
mankind for over a century are the most
versatile and economical ic
engines to release the chemical energy
in diesel effectively an atomized form
of the fuel is made to contact with high
temperature and high pressure air
this energy is effectively transferred
as mechanical rotational energy
so the operation of a diesel engine is
all about producing high temperature and
high pressure air continuously
we will see how this is achieved in this
video
piston
connecting rod
crank
and cylinder form a mechanism called
slider crank mechanism
here the linear motion of the piston is
transformed to a rotary motion at the
crank
in an ic engine this mechanism is
properly supported in an engine block
cylinder head
valves and fuel injector are fitted
above the engine block
when the piston moves downwards inlet
valves open and fresh air from outside
is sucked in or in other words the
engine breathes
during the return stroke inlet and
exhaust valves are closed and the air
inside the cylinder gets compressed
during the compression stroke the piston
does work on the air
so the temperature and pressure of the
air will rise to a level which is higher
than the self-ignition value of the
diesel
an atomized form of diesel is injected
into this compressed air
the fuel gets evaporated and undergoes
an uncontrolled spontaneous explosion
as a result the pressure and temperature
rise to high level values
the high energy fluid pushes the piston
downwards
the hot air does work on the piston and
energy in the fluid is converted to the
mechanical energy of the piston
this is the only stroke where the piston
absorbs power from the fluid
due to inertia of the system the piston
moves upwards again this time the
exhaust valves open and the exhaust is
rejected
again the suction stroke happens
this cycle which has a total four
strokes is repeated over and over for
continuous power production
you may have noticed that a bowl is
provided on top of the diesel engine
piston
during the compression stroke this bowl
helps produce air that is rapidly
swirling
thus the injected fuel gets mixed with
the air effectively
the mechanical design of ic engines
particularly that of diesel engines is a
challenging and interesting task
since the combustion process in diesel
engines is never uniform and smooth they
are prone to more vibration and noise
compared to petrol engines
thus diesel engines require a rugged
structural design
out of the four strokes it is only
during the power stroke that a
tremendous amount of force is exerted on
the piston
so a single cylinder engine will always
have high force non-uniformity as shown
similarly the output power will also
have a fluctuating nature
but with more number of cylinders one
can overcome these problems
consider this four-cylinder engine
here four different strokes can occur at
a time
so the power stroke is always present in
the engine
as a result a four-cylinder engine will
have better force and power uniformity
in short the more cylinders an engine
has the smoother it will operate
a four-cylinder engine generally
operates on the following firing order
a heavy flywheel which acts like a power
reservoir further helps in smoothing out
non-uniformity of power
a huge unbalanced force arises in the
form of dynamic unbalance due to the
excessive mass at the connecting rod
side
this is negated by providing
counterweights on the crank side
opening and closing of valves are
accurately controlled by a pair of cam
shafts
camshafts derive motion from the engine
it is clear that the camshafts need to
rotate at half the speed of crankshaft
we hope you had a nice introduction on
the working of diesel engines
thank you