1. Comparison Between 2-Stroke &
4-Stroke Engine
On the basis ofI. Working principle
II. Engine Design
III. Engine Performance
IV.Cooling and Lubrication System
2. Comparison On the basis of-working principle
4-Stroke Engine
Following are the four
stroke:-
1. Intake/Suction Stroke
2. Compression Stroke
3. Expansion Stroke
4. Exhaust Stroke
3. 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.
4. 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.
5. 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.
6. 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.
7. Working principle of two Stroke
Engine
Two stroke engine is widely used employed where
small power required for motor cycle like auto
rickshaw, scooter.
8. 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,
9. 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.
10. 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
11. 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.
12. Comparison On The Basis Engine Design
4-Stroke
2-Stroke
4-stroke engine is heavy in
weight & required more space.
Because of one power stroke
for two revolution.
4-stroke engine contains valves
and valve mechanism.1.Inlet
Valve & 2.Exhaust Valve.
Exhaust valve shape is larger
than the inlet valve.
2-stroke engine is more
compact and due that it is light
in weight. It is because a 2stroke engine will develop
twice power of a comparable
4-stroke engine because of one
power stroke every revolution.
2-storke engine have no valves
but only ports.1.Inlet Port
2.Outlet Port & 3.Transfer
port.
13. Comparison On The Basis Engine Design
4-Stroke
Shape Of piston Top in
this engine has Flat shape.
Heavier size flywheel is
needed since turning
moment is not so uniform.
2-Stroke
The shape of piston is
deflector type or crown shape.
Top surface is slant surface or
inclination surface.
Lighter Flywheel is needed.
Since more uniform turning
moment is produced.
14. Comparison On Basis Of Engine Performance
4-Stroke
The effective Compression Ratio is
High.
Because of Higher Compression
ratio, The Thermal Efficiency of an
engine is high.
Power Produced for same cylinder
dimensions and speed is less in 4stroke.
2-Stroke
The effective compression ratio in the
case of 2-stroke is less than that for 4stroke engine for the same
stroke(actual) & clearance volume.
Thermal efficiency is low since some
fresh charge escapes during
scavenging process.
Power Produced for same cylinder
dimensions and speed is higher. It is
because, some of the power is used for
compressing the charge in the crank
case and effective stroke is less than
15. Comparison On Basis Of Engine Performance
4-Stroke
Volumetric Efficiency Is High
Due To More Time Available
For Induction.
This engines are less noisy.
This engines are less pollute due
to complete scavenging
operation compare with 2-stroke.
2-Stroke
Volumetric Efficiency Is Low Due To
Less Time Available For Induction.
Sudden release of the gases makes the
exhaust more noisy.
The scavenging is not complete
particularly in high speed engines as
very short time is available for exhaust
& hence the fresh charge is highly
polluted.
The actual efficiency is higher & The actual efficiency of the 2-stroke
better than the 2-stroke engine.
cycle is less than 4-stroke cycle engine
because greater overlapping of the
ports is necessary in this for effective
scavenging.
16. Comparison On The Basis Of Cooling And
Lubrication System
4-Stroke
2-Stroke
Lesser Cooling &
Lubrication is needed
compare with 2-stroke
because of 4-stroke has
only one power stroke per
revolution of crankshaft.
More & efficient cooling &
lubrication is required because of
the power strokes per minute
are twice the power stroke of 4stroke.
Generally water-cooled
system is used in 4-stroke.
Lubricating oil is mixes with fuel
of the engine.
Pressurized Lubrication
System is used.
Normally Air-cooled system is
used in 2-stroke.
The consumption of lubricating
oil is sufficiently large because of
high operating temp.
17. Conclusion
Due to the excessive loss of combustible mixture
with exhaust gases and resultant high fuel
consumption, 2-Stroke cycle engines are not widely
used except in the case of outboard
motors,scooters,motor-cycles and light vehicles.
It is possible to get expected performance of 2stroke engine only if the engine is built for a large
output and good design.
