Working of Four stroke Petrol Engine

IC Engines [Working of Four stroke Petrol Engine]

Working of Four stroke Petrol Engine? Suction or Intake Stroke, Compression Stroke, Working or Expansion or Power Stroke, Exhaust Stroke

Q. Explain working of 4 stroke petrol engine and diesel engine?

Ans:

WORKING OF FOUR STROKE PETROL ENGINE:

In four stroke engines, one cycle is completed with completion of four strokes. Main features of all the strokes are discussed below and their sketch is given in Figure.

Suction or Intake Stroke:

Initially the piston remains n top dead centre (TDC) position, suction valve is open and exhaust valve remains closed. The piston now moves downward and the petrol and air mixture (charge) enters into the cylinder. When piston reaches bottom dead centre (BDC). The cylinder fills with the petrol air mixture. At this moment, suction valve closes. This completes one stroke. Crank turns by 180o, i.e. it completes half revolution.

Compression Stroke

Both the valves (suction and exhaust) are closed. The piston moves upwards from BDC to TDC position. The charge is compressed inside the cylinder, i.e. its pressure increases and volume decreases. Along with pressure temperature also increases. The crank completes next half of revolution.

Working or Expansion or Power Stroke:

When the piston reaches the TDC position spark plug generates spark and the charge is ignited and combustion of mixture takes place. Because of burning of fuel temperature and pressure of gases increases tremendously., both the valves remain closed. The gases expand in the cylinder and push the piston downward and therefore, work is done by the gases on the piston. The crank revolves and completes next half revolution. The reciprocating motion of the piston is converted into rotary motion of crank-shaft by piston rod and crank. During expansion, volume of gases increases. All the power for running the engine is obtained during this stroke.

Exhaust Stroke:

The suction valve remains closed but exhaust valve opens. The piston moves from BDC to TDC. The burnt gases are pushed out of the cylinder due to movement of piston. The cylinder pressure falls down to little above atmospheric pressure. This completes the next half revolution of the crank. By this time, crank shaft completes two revolution and one engine cycle is completed with the completion of four strokes. After this the same process is repeated again and again.