2-Stroke Engine Vs. 4-Stroke Engine: What’s The Difference?

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 What Is A 2 Stroke Engine?

2 Stroke engine cycle

Is a type of internal combustion engine that completes a power cycle with two strokes (up and down movements) of the piston during only one rotation of the Crankshaft. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time. These types of engines usually have a high power-to-weight ratio.

A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate stroke are intake, compression, combustion and exhaust.

What Is A 4 Stroke Engine?

An internal combustion engine that utilizes four distinct piston strokes (intake, compression, power and exhaust) to complete one operating cycle. The piston makes two complete passes in the cylinder to complete one operating cycle.  An operating cycle requires two revolutions of the crankshaft. When compared to 2 stroke engines, 4 stroke engine have greatly increased number of moving parts and therefore, it is more compact and significantly heavier.

The Difference

  1. The 2 stroke engine produces power once every 2 strokes of the piston. It usually generates high torque. On the other hand, the 4 stroke engine takes 4 strokes to produce the power and usually generates less torque for its 2 strokes cycle.
  2. 2 stroke engines require lighter flywheel compare to other engines because it generates more balance force due to one revolution for one power stroke. On the other hand, 4 stroke engines requires heavy flywheel because it generates unbalanced force due to two revolutions for one power stroke.
  3. In 2 stroke engine, the charge is partially burn and mix with the burn gases during inlet due to port mechanism. On the contrary, in 4 strokes engine, charge is fully burn and does not mix with burn charge in ideal condition.
  4. Two stroke engines are less efficient and produce more smoke whereas 4 stroke engines are more efficient and produce less smoke.
  5. In a 2 stroke engine, when the piston goes for the cylinder on top position, it forces the spark to ignite air and when it explodes, it drives the piston downwards. On the contrary, in a 4 stroke engine, when the piston is in the top position to the cylinder, the spark plug burns the air (fuel) and brings the piston down onto the power-stroke and makes the valve close.
  6. Four stroke engines are comparatively heavier than 2 stroke engines due to heavy flywheel and valve mechanism.
  7. 2 stroke engines requires comparatively more lubricating oil than 4 strokes engines because some oil burn with fuel.
  8. 2 stroke engines give less thermal efficiency when compared to 4 stroke engines that give more thermal efficiency (2 stroke engines relatively get hotter when compared to a 4 stroke engine).
  9. 2 stroke engine need regular lubrication because of more wear and tear problem that exist in this type of engine. On the other hand, 4 stroke engines have a complex lubrication system and hence cases of wear and tear are way less.
  10. 2 stroke engines are commonly used in ships, motorcycles, scooter, snowmobiles etc whereas 4 stroke engines are commonly used in road vehicles like trucks, cars and other related automobiles.
  11. Two stroke engines are comparatively cheaper and affordable to 4 stroke engines.
  12. The two stroke engine design is such that there are 2 ports for fuel to get in and out. This design makes its mechanism simpler. On the other hand, 4 stroke engine design is a bit complicated due to the valve that is operated through a chain and gear mechanism.

Read Further: Difference between Diesel and Petrol Engine

2-Stroke Engine Vs. 4-Stroke Engine In Tabular Form

BASIS OF COMPARISON 2-STROKE ENGINE 4-STROKE ENGINE  
Power Production The 2 stroke engine produces power once every 2 strokes of the piston. It usually generates high torque.   The 4 stroke engine takes 4 strokes to produce the power and usually generates less torque for its 2 strokes cycle.
Flywheel Require lighter flywheel compare to other engines because it generates more balance force due to one revolution for one power stroke. Requires heavy flywheel because it generates unbalanced force due to two revolutions for one power stroke.  
Burning Of The Charge The charge is partially burn and mix with the burn gases during inlet due to port mechanism. The charge is fully burn and does not mix with burn charge in ideal condition.  
Efficiency Two stroke engines are less efficient and produce more smoke.   4 stroke engines are more efficient and produce less smoke.
Working Of The Piston When the piston goes for the cylinder on top position, it forces the spark to ignite air and when it explodes, it drives the piston downwards. When the piston is in the top position to the cylinder, the spark plug burns the air (fuel) and brings the piston down onto the power-stroke and makes the valve close.  
Weight Two stroke engines are comparatively lighter than 4 stroke engines.   Four stroke engines are comparatively heavier than 2 stroke engines due to heavy flywheel and valve mechanism.  
Lubrication 2 stroke engines requires comparatively more lubricating oil than 4 strokes engines because some oil burn with fuel.   4-stroke engines require comparatively less lubricating oil than 2 stroke engine.  
Thermal Efficiency Give less thermal efficiency when compared to 4 stroke engines that give more thermal efficiency.   Give more thermal efficiency when compared to 2  stroke engines that give less thermal efficiency
Wear & Tear Need regular lubrication because of more wear and tear problem that exist in this type of engine. Have a complex lubrication system and hence cases of wear and tear are way less.  
Use Commonly used in ships, motorcycles, scooter, snowmobiles etc .    Commonly used in road vehicles like trucks, cars and other related automobiles.
Engine Design Engine design is such that there are 2 ports for fuel to get in and out. This design makes its mechanism simpler. Engine design is a bit complicated due to the valve that is operated through a chain and gear mechanism.  
Affordability Two stroke engines are comparatively cheaper and affordable to 4 stroke engines.   Four stroke engines are comparatively expensive and less affordable to two stroke engines.  

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