Four Stroke Petrol Engine
Four stroke Petrol Engine:
- Cycle of operation completed in four strokes of the piston or two revolution of the crankshaft.
1. Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh air mixed with petrol as fuel is drawn into the cylinder due to the vacuum pressure created by the movement of the piston from TDC to BDC.
2. Compression stroke (both valves closed)-fresh charge is compressed into clearance volume by the return stroke of the piston and ignited by the spark for combustion. Hence pressure and temperature are increased due to the combustion of fuel.
3. Expansion stroke (both valves closed)- The compressed mixture is ignited by the spark plug spark. The combustion leads to the production of high pressure gases. Due to this tremendous force the piston is driven back to the bottom of the cylinder. As the piston moves downwards, the crankshaft rotates which rotates the wheels of the vehicle.
4. Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out due to the movement of piston from BDC to TDC.
