Petrol (or gasoline) powers a car engine through a series of steps that involve combustion, which is the process of burning fuel to release energy. Here's how it works:

1. Fuel Injection or Carburetion:

- In modern cars, petrol is injected into the engine's cylinders by a fuel injection system, while older vehicles may use a carburetor.

- The fuel mixes with air in the intake manifold to form an air-fuel mixture.

2. Compression:

- The air-fuel mixture is drawn into the cylinder as the piston moves downward during the intake stroke.

- The piston then moves upward during the compression stroke, compressing the air-fuel mixture. This increases the pressure and temperature of the mixture, making it more volatile and ready for ignition.

3. Ignition:

- At the top of the compression stroke, the spark plug ignites the compressed air-fuel mixture. This is done using an electric spark generated by the car's ignition system.

- The spark causes the mixture to burn rapidly, releasing a large amount of energy in the form of expanding gases.

4. Power Stroke:

- The rapid expansion of gases from the combustion pushes the piston downward with great force. This movement is converted into rotational motion by the crankshaft, which ultimately turns the wheels via the transmission and driveshaft.

5. Exhaust Stroke:

- After the power stroke, the piston moves upward again in the exhaust stroke, pushing the burnt gases out of the cylinder through the exhaust valve.

- These gases are expelled into the exhaust system and eventually released into the atmosphere.

6. Recycling the Process:

- The cycle begins again with the intake stroke, drawing in a new air-fuel mixture, and the process repeats continuously as long as the engine is running.

Key Components:

- Piston: Moves up and down within the cylinder to convert the energy of combustion into mechanical work.

- Crankshaft: Converts the linear motion of the pistons into rotational motion to drive the wheels.

- Spark Plug: Provides the spark needed to ignite the air-fuel mixture.

- Valves: Control the flow of air, fuel, and exhaust gases into and out of the cylinder.

- Fuel System: Supplies petrol to the engine at the right pressure and quantity.

Summary:

Petrol-powered engines work on the principle of internal combustion, where the controlled burning of petrol creates high-pressure gases that push the pistons. This mechanical energy is then converted into rotational motion to propel the vehicle forward.