4-STROKE PROCESS

At present 4-stroke engines are commonly used because of their higher efficiency than 2-stroke engines. They emit very low carbon monoxide comparing to 2-stroke engines.The process involved in four stroke engines is:
               *Suction
               *Compression or ignition
               *Expansion or Power stroke
               *Exhaust.


1.SUCTION:
                    During suction the piston inside the cylinder undergoes downward movement from the top; sucking the air and fuel mixture from the carburetor and from the fuel pump.At this time the inlet valve opens and allows the air,fuel mixture in to the cylinder.The exhaust valve is closed at this time


2.COMPRESSION:
                               During this process both inlet valve and exhaust valves closed, the piston returns to the top of the cylinder compressing the air, or fuel-air mixture in the cylinder.

3.EXPANSION OR POWER STROKE:

                               In this process when the piston reaches close to the TDC during the second stroke(COMPRESSION),the spark is ignited and the large amount of heat developed during that process in TDC pushes the piston down causing the third stroke with enormous amount of energy released.

This is the power stroke of the piston and this stroke gives maximum power to the engine.At this stroke both inlet and exhaust valves remain closed.

4.EXHAUST:

                 After completing the power stroke the piston reaches the TDC again and now the outlet valve is opened and the gases are sent out through it.

                 

                 This process continues as long as the engine is running.

                                                       1.WORKING OF 4-STROKE ENGINE