One common way is if the fuel tank is punctured and gasoline comes into contact with a spark or other source of ignition. This can happen in a car accident, or if the car is intentionally set on fire.
Another way is if the engine overheats and the coolant ruptures. This can cause the engine block to crack and allow pressurized oil to escape. If the oil comes into contact with a spark or other source of ignition, it can explode.
Finally, cars can also explode if the electrical system is damaged. If a wire shorts out and creates a spark, it can ignite any nearby flammable materials, such as gasoline or oil.
