Four Stroke Cycle Engines - 4 stages of a 4 stroke engine

Four stroke petrol engine is based on principle of theoretical otto cycle which is also known as constant volume cycle.Because during this process the volume is constant.

Nikolaus Augjust otto who build first petrol engine in 1876.

Basic construction of Four stroke petrol engine

The valve operating the inlet is called inlet valve and the valve operating exhaust is called as exhaust valve. The spark plug is fitted on the top of cylinder head which ignition mixture of air and petrol. Another parts of the engine are cylinder, valves(inlet and exhaust valves),crank,connecting rod, cranck shaft,Carburetor etc
For more information of engine parts check on this link Various Engine parts

The piston performs following four stroke to complete one running cycle.

Also shows below the basic figure and construction of four stroke petrol engine.

Four Strokes Of An Engine

Basically in the working of four stroke petrol engine four strokes are performed which is discussed but first we clear the terminology of some words which is related to I.C. engine

What is stroke ?

Stroke is defined as linear distance traveled by the piston when it moves from one end of the cylinder to the another end. Which is equal to twice the radius of crank which is convert linear motion of piston to rotational motion of the crankshaft.

T.D.C. (top dead center )

Top most position of the piston

B.D.C. (Bottom Dead center )

Bottom most position of the piston

Now we clear working of four strokes

Suction stroke:

Suction stroke in which the initial position of the piston is at Top dead center which moves and reaches to the Bottom dead center due to this movement the the volume in cylinder will be increased. Before this movement the pressure of Cylinder is at atmospheric pressure but after this movement the pressure is decreases and the pressure difference is developed between inside the cylinder and outside the cylinder.
Due to this mixture of air and fuel is intake from intake valve through carburetor. At the end of this process the crankshaft will rotate at the angle of 180° and the position of piston is at Bottom dead center also cylinder is fill of Petrol and air mixture then inlet valve closed

Compression stroke:

In this stroke both valves (inlet valve and exhaust valve) are closed and the initial condition of the piston is Bottom dead center which moves Bottom dead center to Top dead center and during this process pressure and temperature of the air and petrol mixture will be increased. Then at the end of stroke spark plug  Ignited the mixture of air and petrol at the constant volume and hot gasses are produced.so the spark plug ignites the mixture of air and petrol in this stroke.

Power or expansion stroke:

During this stroke both inlet and exhaust valves are closed and initial position of the piston Is Top dead center which moves from Top dead center to Bottom dead center. Mixture of Hot gases and petrol are burnt and pressure will increased due to this combustion of air and petrol is force the piston to make this stroke.
Due to that this stroke is also known as working stroke or power stroke.
The mechanical energy is developed in this stroke for produce some work. Then due to combustion of hot gases piston moves towards the Bottom dead center and volume of cylinder will be increased and pressure will be decreased gradually. Near the end of this stroke exhaust valve will open and hot gases is release in atmosphere and then pressure of cylinder is equal to atmospheric pressure.

Exhaust stroke:

During this stroke inlet valve is closed and exhaust valve is open. Piston moves from Bottom dead center to Top dead center and piston pushes the exhaust gases fue to that combustion product (burnt mixture of air and petrol) is released in to atmosphere at atmospheric pressure exhaust stroke is fully work with atmospheric pressure.

After exhaust stroke again inlet valve opens and above described cycle proceed till engine stops working.
So as explained above engine performs four stroke continuity and produce power for done some work.engine is also one type of prime mover.As explained engine converts mechanical energy to chemical energy.

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