What is four stroke engine?

Last Updated on 22 July 2024 by Technical Education

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.