Diesel Engine, How it works ?

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


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


in an IC engine this mechanism is

properly supported in an engine block


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 breathe

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


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 powerstroke 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

counter weights on the crank side

opening and closing of valves are

accurately controlled by a pair of


camshafts derive motion from the engine

it is clear that the camshafts need to

rotate at half the speed of crankshaft

we hope you have a nice introduction on

the working of diesel engines thank you