The internal combustion engine is one of the most important inventions in modern history. It converts chemical energy from fuel into mechanical energy, which powers most cars, motorcycles, and many other machines. The four-stroke cycle, invented by Nikolaus Otto in 1876, is the most common type of internal combustion engine.

1. Intake Stroke

• The intake valve opens.

• The piston moves downward, creating a vacuum.

• The air-fuel mixture enters the cylinder.

2. Compression Stroke

• Both valves are closed.

• The piston moves upward, compressing the air-fuel mixture.

• The mixture becomes highly pressurized.

3. Power (Combustion) Stroke

 

• A spark plug ignites the compressed mixture.

• The explosion pushes the piston downward.

• This is the stroke that produces useful mechanical power.

4. Exhaust Stroke

• The exhaust valve opens.

• The piston moves upward again.

• The burned gases are expelled from the cylinder.