FOUR STROKE ENGINE

Working Principle Of Four Stroke Engine

2. Engine
An engine is motor which
converts chemical energy
into mechanical energy

3. History
•Otto Cycle: Dr. Nicolaus Otto -1876

4. History
One of the most important landmarks in engine
design by Nicolaus August Otto in 1876 who is
invented as effective four stroke engine.that's why
it is also called as “Otto cycle engine”.
In 1885,German mechanical
engineer,Karl Benz designed and built the
world's first practical automobile to be
powered by an internal-combustion
engine. On January 29,1886.

5. •2-Cycle Engine; Du gal Clerk -1878
History

6. •Diesel Engine; Dr. Rudolph Diesel -1895
History

7. Four Stroke Engine
Four stroke engine was first demonstrate by
Nikolaus Otto in 1876,hence it is also known
as Otto cycle. It consist of 4 stroke ,one cycle
operation is completed in 4 stroke of the
piston, That is one cycle is completed in every
2 revolutions of the crankshaft. Each stroke
consist of 180°,of crankshaft rotation and
hence a cycle consist of 720°,of crankshaft
rotation.

8. Working principle of
four Stroke Engine
Following are the four strokes
1 – Intake/Suction stroke
2 – Compression stroke
3 – Expansion stroke
4 – Exhaust stroke

9. 1 – Intake stroke
In suction stroke piston starts at Top
Dead Center (TDC) of the cylinder
and moves to the Bottom Dead
Center (BDC).
Outlet valve will be closed
and inlet valve will be open to
allowing the fresh charge of mixed
fuel & air into the cylinder.

10. 2 – Compression stroke
In compression stroke,Once piston
reaches BDC & moves back
TDC,inlet valve will be closed,As
the piston moves towards TDC,It
compress air fuel mixture inside
the cylinder & compression takes
place,Hence it is called
compression stroke.

11. 3 – Expansion stroke
In expansion stroke,Both the
valves are closed,When piston
reaches top of its stroke the fuel
mixture is ignited by spark plug
due to spark high temperature &
pressure generated inside the
cylinder & push down the piston to
BDC,Hence it is known as
expansion stroke.

12. 4 – Exhaust stroke
In this stroke exhaust valve is
opened,when piston reaches to
BDC & moves to upward.
Piston pushes out the burnt gases
to the atmosphere through the
exhaust valve. Hence called
exhaust stroke & the engine is
ready to begin the cycle again.

13. Parts of an engine

14. Various Parts of Engine
•Crankshaft
•Crankcase
•Crank Pin
•Camshaft
•Spark plug
•Fuel pump
•Cylinder Block
•Cylinder Head
•Inlet valve &
Exhaust valve
•Piston
•Piston Rings
•Connecting Rod
•Gudgeon Pin

15. Cylinder Block
The cylinder block, also called as
engine block is the main bottom end
structure. Usually it is made up of
iron or aluminum.
Function: In the bore of the cylinder
the fresh charge of air-fuel mixture
is ignited,compressed by piston.

16. Cylinder Head
The cylinder head is flat plate of
metal bolted to the top of cylinder
block with head gasket in
between;Top of head contains
rocker arm & push rod to transfer
rotational mechanic from the
crankshaft to linear mechanic to
operate the valves. It is the key to
performance of the internal
combustion chamber.

17. Inlet valve & Exhaust valve
Inlet valve:Its function is to intake
the fresh air-fuel mixture into the
cylinder.
Exhaust valve:Its function is to
exhaust is the burnt gases by the
force of piston.

18. Piston
Piston is connected to the crankshaft
through the connecting rod,when
piston moves downward sucks fresh
air-fuel mixture in suction stroke &
ignited inside the cylinder due to
this high temperature and pressure
generated,thus expanded gas force
down to piston.

19. Piston Rings
A piston ring is an open ended ring
that fits into a groove or outer
diameter of the cylinder. Piston
rings have three major functions
which are to seal the expansion
chamber,support heat transfer &
finally,regulate the engine oil
consumption.

20. Connecting Rod & Gudgeon Pin
A small end of connecting rod is
connected to the piston and other
end is connected to the crankshaft.
Its function is to transmit the
reciprocating motion of piston to the
to the rotary motion of crankshaft.
Gudgeon pin is used to connect the
piston & connecting rod.

21. Crankshaft
Crankshaft is the part of an engine
which translates the reciprocating
linear motion of piston into
rotation. To convert the
reciprocating motion into
rotation,the crankshaft has “crank
pin”,it typically connects to
flywheel,to reduce the pulsation
characteristics four stroke cycle.

22. Crankshaft
The crank-connecting rod is first fully developed
by Arab inventor Al-Jazari in (1136-1206).Similar
crankshaft late described by Conrad Keyser in
1405.The main function of crankshaft is receives
the oscillating motion from connecting rod and
gives rotary motion to main shaft. It also drives the
camshaft which actuate the valves of the engine.

23. Camshaft
Camshaft is a part which is used in
piston engine to operate valves. It
consists of cylindrical rod with
cams. The camshaft were invented
in Iraq (Mesopotamia), described
by Al-Jazari in 1206.The
relationship between camshaft
rotation & crankshaft rotation is of
critical importance.

24. Camshaft
Since valves controls the flow of air-fuel mixture
intake & exhaust burnt gases. Valves must be opened
& closed at appropriate time during the stroke of
piston,For this reason ,the camshaft is connected to
the crankshaft either directly,via a gear mechanism,
or indirectly via belt/chain called a timing belt or
timing chain, the camshaft rotates at the same rate of
crankshaft.

25. Spark Plug
Spark plug is used in petrol engine
only which is help to ignite the air-
fuel mixture for combustion.

26. Two Stroke Engine
Two stroke engine is first described by Du gal
Clerk in 1878.In two stroke engine one cycle
is completed in every revolution of
crankshaft.

27. Working principle of
two Stroke Engine
Two stroke engine is widely used employed where
small power required for motor cycle like auto
rickshaw, scooter. This type of engine is compact in
size,easy for manufacturing and simple in operation.
In two stroke engine there are no inlet or exhaust
valve as in four stroke engine.

28. Working principle of
two Stroke Engine
But only inlet & exhaust ports used ,Due to which
suction & exhaust stroke is eliminated in two stroke
cycle engine.

29. Compression Stroke
When piston moves from BDC to
TDC,it first closes the transfer port &
then exhaust port,The charge of air-
fuel mixture in the chamber is
pressurised & creates high
temperature. At the same time,

30. Compression Stroke
a vacuum is developing in the crankcase,so the fresh
charge of fuel mixture is being drawn into the
crankcase from the carburettor. As the piston moves
towards TDC ,a high voltage discharge from the spark
plug & ignites the air-fuel mixture in the combustion
chamber.

31. Combustion Stroke
In this stroke both the ports still
closed condition,the pressure of the
expanding gases forces the piston
towards BDC.the pressure in the
crankcase is already rising. Later in
down stroke exhaust port will be
open & forced out the burnt
gases,Very shortly after that the

32. Combustion Stroke
Inlet / Transfer port will also open to intake the fresh
charge of fuel mixture,and engine is ready to start of
the cycle.

33. Advantages & Disadvantages of
Two Stroke Engine
•One cycle completed in every revolution of
crankshaft.
•It is more compact,required less space and lighter
in weight than four stroke engine.
•The design & construction is much simpler than
four stroke engine.
•Easy to manufacture & low cost.
Advantages :

34. Advantages & Disadvantages of
Two Stroke Engine
•There is no suction and exhaust valve used,hence
no need of cam,camshaft and rocker arm etc.
•Gives less torsional oscillation.
•Requires less spare parts.
•Easy for maintenance.
Advantages :

35. Advantages & Disadvantages of
Two Stroke Engine
•High fuel consumption.
•Compression ratio and thermal efficiency is less
than that of four stroke engine of the same
dimension.
•Consumes more lubricating oil.
•More wear & tear of moving parts hence it gives
loud noise.
Disadvantages :

36. Difference between
4-Stroke Engine & 2-Stroke Engine
•One cycle completed
in every 2 revolution
of crankshaft
•More moving parts
•More maintenance
•Heavy in weight
•More expensive
•One cycle completed
in every revolution of
crankshaft
•Less moving parts
•Less maintenance
•Light in weight
•Less expensive
4-Stroke Engine 2-Stroke Engine

37. Difference between
4-Stroke Engine & 2-Stroke Engine
•Produce more
pollution
•Long engine life
•Not required
•Complex design
•Less pollution
•Short engine life
•Required a mix of oil
to lubricate the
crankshaft
•Simpler design
4-Stroke Engine 2-Stroke Engine