Four stroke engine .
Stroke is defined as the movement of the piston from the ‘bottom dead centre ‘ (BDC) to the ‘top dead centre’ (TDC) or the other way round, that is from TDC to BDC. A four stroke engine has 4 strokes.
1º Intake.
2º Compression
3º Power
4º Exhaust.
| 4 Stroke engine | |
|---|---|
 |
 |
1. IntakeThe piston is at its highest point (TDC), the inlet valve opening and the exhaust valve closed. The piston moves downward and it increases the volume between the valves and the piston, so the pressure inside the cylinder gets lower and lower. As the outside air pressure is higher, this forces the air-fuel mixture into the cylinder as the piston is moving down. A moment later, the piston reaches the BDC ( bottom dead centre) and the inlet valve closes. A new stroke is coming. |
2. Compression. Both exhaust and intake valves stay closed as the piston moves upward from the BDC (bottom dead centre) The piston moves upward, squeezing the fuel-air mixture into a smaller volume. The pressure gets higher and this causes the fuel-air mixture’s temperature to rise. With high temperature, ignition is easier and combustion more complete |
  |
|
| 3. Ignition and Power: Just before the piston reach the TDC ( At the end of the compression stroke ) the spark plug fires. The fuel-air mixture explodes forcing the piston down the cylinder. The power stroke drives the engine | |
 |
 |
| 4 Exhaust.At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism.The piston now moves from BDC to TDC. The inlet valve is closed, the exhaust valve opens, and the piston, moving upward, pushes the leftover gases out of the cylinder. BDC = bottom dead centre TDC = top dead centre | Stroke engine Illustration. |