1. Intake Stroke:
- The piston moves downwards, creating a vacuum in the cylinder.
- The intake valve opens, allowing air and fuel mixture to enter the cylinder.
2. Compression Stroke:
- The piston moves upwards, compressing the air-fuel mixture.
- Both intake and exhaust valves are closed.
- This compression increases the temperature and pressure of the mixture.
3. Power Stroke:
- A spark plug ignites the compressed air-fuel mixture, causing a rapid expansion and pushing the piston downwards.
- This is the power stroke, converting chemical energy into mechanical energy.
- The exhaust valve remains closed.
4. Exhaust Stroke:
- The piston moves upwards, pushing the burnt gases out of the cylinder.
- The exhaust valve opens, allowing the gases to escape.
- The intake valve remains closed.
Cycle Repetition:
After the exhaust stroke, the cycle repeats, starting with the intake stroke again.
Key Features:
- Four strokes per cycle: The engine completes all four strokes for each power cycle.
- Otto Cycle: The four-stroke engine operates on the Otto cycle, which is a thermodynamic cycle describing the working of internal combustion engines.
- Spark Ignition: Fuel is ignited by a spark plug, triggering combustion.
- Air-Fuel Mixture: The engine requires a precise mixture of air and fuel for efficient combustion.
Advantages of Four-Stroke Engines:
- Higher Efficiency: Compared to two-stroke engines, they generally have higher thermal efficiency.
- Lower Emissions: Due to better combustion and a separate lubrication system, they produce fewer emissions.
- Smoother Operation: The four-stroke cycle provides a smoother power delivery.
Disadvantages of Four-Stroke Engines:
- More Complex: The design is more complex than two-stroke engines.
- Heavier: They are typically heavier due to their more complex design.
Overall, four-stroke petrol engines are widely used in automobiles, motorcycles, and various other applications due to their balance of efficiency, emissions, and performance.
