Working of 4 stroke Petrol Engine

4 stroke petrol engines are widely used in car, bikes etc. It is also known as SI (spark ignition) engine because combustion in petrol engine initiates from a spark. It is based on Otto cycle.  It has four strokes i.e suction, compression, expansion (power) and exhaust stroke. Thus each stroke comprises of 180 degree rotation of the crankshaft.
Petrol Engine

The first practical petrol engine is build by Nikolaus August Otto in 1876 in Germany.



Nikolaus August Otto


Working of 4 stroke petrol engine :-


Suction stroke :- In this stroke piston moves from TDC to BDC and in the mean time inlet valve get opened. Due to the downward movement of piston a low pressure is developed inside the combustion chamber which cause the intake of  the air fuel (petrol) mixture. Intake valve remained opened till the piston reaches BDC.
Suction stroke

Compression stroke :- In this stroke the piston start moving toward TDC and because of both intake and exhaust valves are closed the air fuel mixture inside the combustion chamber start compressing. This stroke continous till the piston approaches TDC.
Compression stroke

Power or Expansion stroke :- At the starting of this stroke i.e when piston is on TDC the spark plug ignites the spark. Due to the spark the compressed air fuel mixture ignites and combustion take place. Due to this the pressure inside the combustion chamber increases which pushes the piston toward BDC. This is the part where power is produced by the engine.
Power stroke

Exhaust stroke :- This stroke take place after expansion stroke. This stroke starts from BDC and the piston is moving toward TDC. In the mean time the exhaust valve get open. As the piston is moving upward it pushes out the exhaust gases present inside the combustion chamber outside from exhaust valve.

Exhaust stroke

In the below image we can see  all 4 strokes in a working engine.

Advantages of 4 stroke petrol engine :-
  • Less fuel consumption.
  • Emits less amount of  harmful gases.
  • High efficiency as compare to 2 stroke engine.
  • Long life.
  • Higher speed than diesel engine.
Disadvantages of 4 stroke petrol engine :-
  • Complicated design.
  • Need more components as that of 2 stroke engine.
  • Expensive.
  • Less thermal efficiency as that of diesel engine.
  • Need more maintenance.

Applications of 4 stroke petrol engines :-
  • Cars 
  • Motorcycles
  • Aircraft
  • Motorboats
  • Chainsaw
  • Portable engine generator



Comments

Post a Comment