Engines

• What is a 4-stroke engine

  burns fuel ONCE every 4 strokes of the piston
• What are the 4 strokes in a 4 stroke engine:

  • Induction
  • Compression
  • Expansion
  • Exhaust
• Induction:

  • Piston goes down, volume of the gas above increases
  • Fuel and air mixture gets into the engine from the inlet valve
  • Pressure of the gas remains constant
• Compression:

  • The inlet valve is closed, Piston moves back up
  • Pressure increases
  • Just before the end of the stroke, a spark occurs
  • The pressure and temperature increases dramatically at constant volume
• Expansion:

  • The air-fuel mixture expands does work on the piston
  • The work it does > Work required to compress the gas (net output of energy)
  • Just before the piston is at the bottom of the stroke, the exhaust valve opens and the pressure goes down
• Exhaust:

  • Piston moves back up the cylinder and the burnt air-fuel mixture leaves through the exhaust valve
• Diesel Engines:

  • Also 4 - strokes:

  1. Only air goes into the cylinder during the induction stroke
  2. During the compression stroke, the air is compressed at high enough temperature to ignite the diesel fuel. Before the end of the stroke, fuel injectors inject diesel fuel
  3. Expansion and Exhaust strokes are similar