How a Petrol Engine Works

A petrol engine (also called a gasoline engine) is an internal combustion engine that converts fuel into mechanical power. Unlike diesel engines, petrol engines use spark plugs to ignite the fuel–air mixture.

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1️⃣ Air and Fuel Intake

When the piston moves downward:

• Air enters the cylinder

• Petrol is mixed with the air (by a carburetor or fuel injector)

This creates a fuel–air mixture inside the cylinder.

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2️⃣ Compression

The intake valves close and the piston moves upward.

• The fuel–air mixture is compressed

• Compression increases pressure and temperature

However, compression is lower than in diesel engines.

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3️⃣ Ignition (Spark)

At the top of compression:

• The spark plug produces a spark

• The spark ignites the fuel–air mixture

• A controlled explosion occurs

This explosion forces the piston downward.

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4️⃣ Power Stroke

The downward movement of the piston:

• Turns the crankshaft

• Produces mechanical power

• Moves the vehicle

This is the stroke that generates usable energy.

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5️⃣ Exhaust

After combustion:

• Exhaust valves open

• Burned gases leave the cylinder

• The cycle starts again

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🔁 Four-Stroke Petrol Engine Cycle

1. Intake

2. Compression

3. Ignition & Power

4. Exhaust

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✅ Advantages of Petrol Engines

• Smooth and quiet operation

• Lower initial cost

• Faster acceleration

• Simpler fuel system

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⚠️ Disadvantages of Petrol Engines

• Higher fuel consumption

• Less torque than diesel engines

• Shorter lifespan under heavy use

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🚗 Common Uses of Petrol Engines

• Passenger cars

• Motorcycles

• Small generators

• Light commercial vehicles

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🧠 Conclusion

Petrol engines are ideal for everyday driving thanks to their smooth performance and lower cost. They are best suited for city use and light-duty applications.