What is four stroke engine?

What is Four stroke- 

A four-stroke engine is an internal combustion engine where the piston completes four separate strokes while turning the crankshaft.  This cycle is partially formed by the German scientist Otto in 1876, although it was described by French scientist Beande Roches in 1862. Each and every stroke are completed with 180⁰ turning of the crankshaft.  The four strokes are- Suction, Compression, Power, and Exhaust.

 

1.     Suction Stroke- 

      During the suction stroke, the piston is moved from T.D.C to B.D.C by the crankshaft, which is revolved either by the momentum of the flywheel or by the power generated by the electric starting motor. The inlet valve remains open and the exhaust valve is closed during the stroke. The downward movement of the piston sucks air and fuel mixture in the cylinder from the carburetor through the open inlet valve. In the diesel engine, only air was sucked into the cylinder. Here the crankshaft revolves around 180⁰.

2.   Compression Stroke-

      During the compression stroke, the piston moves upward. The piston compresses the air-fuel mixture and the heat generated into the cylinder, makes a homogeneous mixture (14.7:1). The heat makes the petrol easier to burn while the compression forces it into closer combination with the air.  The mixture under compression is ignited by the spark produced by a spark plug while the piston moves from B.D.C to T.D.C. Both the inlet and exhaust valve remains closed in this stroke. The crankshaft rotates at 180⁰

3.   Power stroke-

     The power stroke is known as a working or expansion stroke. The expansion of the gases due to the heat of combustion exerts pressure on the piston. Under this pressure, the piston then moves from T.D.C to B.D.C and does the useful work. Both valves remain closed during the stroke. Here the crankshaft rotates 180⁰.

4.  Exhaust Stroke-

     During this stroke, the inlet valve remains closed and the exhaust valve opens. The greater part of the burnt gases escapes because of their own expansion. The piston moves from B.D.C to T.D.C and pushes the remaining gases out of the exhaust valve. Only a small amount of exhaust gases remains in the clearance space which dilutes the fresh incoming charge. Here the piston rotates 180⁰.

 

Thus the four stoke was completed with the help of the piston and crankshaft. The crankshaft rotates a total of 720⁰ to complete all the strokes.

Here The T.D.C means the top dead center into the cylinder, where the piston head appears.

The B.D.C means the bottom dead center of the cylinder.