1. Intake Stroke:
* Piston Movement: The piston moves downwards, creating a vacuum in the cylinder.
* Purpose: This draws in a mixture of air and fuel (or just air in the case of diesel engines) into the cylinder.
2. Compression Stroke:
* Piston Movement: The piston moves upwards, compressing the air-fuel mixture.
* Purpose: This increases the pressure and temperature of the mixture, preparing it for combustion.
3. Power Stroke:
* Piston Movement: The compressed air-fuel mixture is ignited by a spark plug (gasoline engine) or by the high temperature and pressure (diesel engine). The resulting explosion forces the piston downwards.
* Purpose: This is where the engine's power is generated.
4. Exhaust Stroke:
* Piston Movement: The piston moves upwards, expelling the burned gases out of the cylinder through the exhaust valve.
* Purpose: This clears the cylinder for the next intake stroke.
Cycle Completion:
* After the exhaust stroke, the intake valve opens again, and the cycle repeats.
Key Points:
* Each stroke is driven by the crankshaft, which is connected to the piston via a connecting rod.
* The timing of the valve openings and closings is controlled by the camshaft, which is also connected to the crankshaft.
* The four strokes occur in a specific sequence, with the power stroke being the only one where mechanical work is produced.
Simplified Analogy:
Imagine a bicycle pump:
* Intake: Pulling the handle down creates a vacuum, drawing air into the pump.
* Compression: Pushing the handle up compresses the air.
* Power: The compressed air is released, pushing the pump's nozzle down.
* Exhaust: The handle is pulled up again, releasing the used air.
This analogy, although simplified, demonstrates the basic concept of the four-stroke engine cycle.
