What is Difference Between 2 stroke and 4 stroke engine

The Basic Difference Between 2 stroke and 4 stroke engine cycles resides in the movement of crankshaft and piston in one revolutions.

I.e In 2 stroke engine,in one power stroke one revolutions of crankshaft complete and in 4 stroke engine two complete revolution of crankshaft occur in one power stroke.


Difference between 2 stroke engine and 4 stroke engine


Before starting difference between two stroke engine and four stroke engine ,first we understand about two stroke engine and four stroke engine in details. 

In today’s article we are going to learn about 2 stroke and 4 stroke engine. What is the difference between 2 stroke engine and 4 Stroke engine and which one is better and why. All these questions will be answered in subsequent paragraphs.

What is a Two Stroke Engine ?

2 stroke engine

2 stroke engines are those engines in which all the four cycle of the combustion i.e Suction, compression, Power, and exhaust are completed in 2 stroke of the piston .

When the piston is at BDC the fresh charge air comes into the cylinder and as the piston moves upward and starts covering the ports the compression starts.

The piston reaches TDC where the ignition takes place and the fire force push the piston downwards which is known as the power stroke.

As soon as the piston starts coming near to BDC, the exhaust port is uncovered and exhaust gases are expelled out. And the process continues.

As mentioned in the beginning all the process need just two stroke of the piston.

In first stroke, Suction and Compression takes place and in second stroke Power and exhaust Takes place.

Two stroke engines are generally slow speed engines and are simpler in construction. Thus making them cheaper as compared to the 4 stroke engines.

As we see in 2 stroke engine we get power stroke in every alternate stroke of the cycle so the forces and load on flywheel will be uniform. Thus we can use smaller flywheels in 2 stroke engines.

Also Read : Easiest Way to Calculate Brake Horsepower

4 Stroke Engine

The 4 stroke engines are those engines in which the all the four process i.e Suction, Compression, Power and exhaust is completed in four strokes of the piston.

When the piston moves downward it sucks air into the cylinder, then in next upward stroke the air is compressed, After firing the Piston moves downward in the power stroke and in final upward stroke the piston expells out the exhaust gases out of the cylinder.

Thus every action is performed by an individual stroke. Four processes, Four strokes, hence called as 4 Stroke engine.

The Power stroke in a 4 stroke engines comes in every 3rd stroke after the commencement of 1st Power stroke.

So the flywheel has to store more energy and hence it’s size is comparatively larger.

It is used in high speed engines and are generally costlier than the 2 stroke engines.

Difference Between 2 stroke and 4 stroke Engine Table

S.NO                   2 STROKE                        4 STROKE
1. In 2 stroke Engines ,all the four processes of cycle is done in one revolution of the crankshaft. In 4 stroke Engine ,all the four processes of cycle is done in two revolution of the crankshaft.
2. power is generated in every alternate strike of the piston. Power is generated in every 3rd stroke after the first power stroke.
3. Two stroke engine have inlet and exhaust ports (exhaust valve in case of of uni flow scavenging). use of port for inlet and outlet of gases. Four stroke engine have valve mechanism for inlet and exhaust ( use valve to inlet and outlet of gases )
4. In two stroke engine  engine,2 process are done simultaneously in every stroke (suction & compression in 1st  and power & exhaust in 2nd. ) In four stroke engines , all the processes are done in individual strokes.
5. Compatible for for burning heavy fuel oil. Difficulty in burning heavy fuel oil.
6. low power to weight ratio. high power to weight ratio.
7.  It requires smaller flywheel (Because  two stroke engine generates more balanced force due to one revolution in one power stroke ) It requires larger flywheel ( Because it generates  unbalanced force due to two revolutions in one power stroke.)
8. They are generally slow speed engines. They are generally High speed engines
9. It Generates High Torque as compare to four stroke engine. Generates low Torque  ( It is due to only 2 revolution of crankshaft b/w one power stroke.
10. Less thermal efficiency High thermal efficiency
11. Cheaper Costly
12. Simple Design Tough to Manufacture
13. Noisy Less Noisy
14. Easy Lubrication  ( Due to Mixing of Lubrication Oil With the fuel ) Comparatively Complex lubrication.


What are constructional Differences between 2 stroke and  Stroke Engines ?

The constructional difference is that 2 stroke use port for inlet and outlet of gases while 4 stroke engine require valve.

In two stroke engine the piston itself open and closes inlet and exhaust port  instead of valve mechanism used in 4 strike engine.

Two stroke engine do not require poppet v/v ,springs or cams.The valves are part of the cylinder which open or close by valve mechanism or rotary 7 reed valves used in crankcase in some design.



Also Read: Crankcase Explosion

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