FOUR STROKE ENGINE PARTS AND WORKING

1. What is a Four-Stroke Engine?

A four-stroke engine is an internal combustion engine where the piston completes four separate strokes (movements up and down) to complete one power cycle. The four strokes are:

  1. Intake
  2. Compression
  3. Power (Combustion)
  4. Exhaust

It is widely used in cars, motorcycles, and generators because it’s efficient and durable.

2. Main Parts of a Four-Stroke Engine

  1. Cylinder – A chamber where fuel combustion occurs.
  2. Piston – Moves up and down inside the cylinder, transferring energy to the crankshaft.
  3. Connecting Rod – Connects the piston to the crankshaft and converts reciprocating motion into rotational motion.
  4. Crankshaft – Rotates and delivers power to the vehicle’s drivetrain.
  5. Cylinder Head – Covers the cylinder; contains intake and exhaust valves.
  6. Valves

    • Intake valve – Allows air-fuel mixture to enter.
    • Exhaust valve – Lets burnt gases exit.

  7. Spark Plug (in petrol engines) – Ignites the fuel-air mixture.
  8. Camshaft – Operates the valves in synchronization with the piston movement.
  9. Flywheel – Maintains engine momentum and smooth operation.

3. Working of a Four-Stroke Engine

Stroke 1: Intake Stroke

  • Piston moves downward.
  • Intake valve opens, allowing air-fuel mixture (in petrol engine) or air only (in diesel engine) into the cylinder.
  • Exhaust valve remains closed.

Stroke 2: Compression Stroke

  • Piston moves upward.
  • Both valves are closed.
  • Air-fuel mixture gets compressed, increasing pressure and temperature.

Stroke 3: Power Stroke

  • Spark plug ignites the compressed mixture (petrol engine).
  • Rapid combustion forces the piston downward, producing mechanical power.
  • This is the stroke that actually drives the vehicle.

Stroke 4: Exhaust Stroke

  • Piston moves upward again.
  • Exhaust valve opens, pushing burnt gases out of the cylinder.
  • Intake valve remains closed.

Cycle Repeats

  • After the exhaust stroke, the cycle starts again with a fresh intake stroke.
  • Two revolutions of the crankshaft are required to complete one power cycle in a four-stroke engine.

✅ Key Points:

  • Produces power every two revolutions of the crankshaft.
  • More fuel-efficient and smoother than a two-stroke engine.
  • Common in cars, motorcycles, and light trucks.