What causes combustion in cars?

when air and petroleum react with each others, combustion occur.

Explanation:

Combustion is a process of burning. It is the chemical process in which heat is released to perform the work by the burning of fuel and air mixture.

It is occur in engine. In engine a moveable piston and cylinder is present. Cylinder is made up of metal and having piston at one end. At the top two valves are present. One is inlet where the fuel and air can inter while from outlet valve gases can escape.

In vehacals fuel is present in the form of petroleum. It is black thick liquid. It mainly consist of hydrocarbon. That's why when air and petroleum react with each others, combustion occur. It form carbon dioxide and water and heat is also released. This energy push the piston which intern drive the wheels.