Question

on what principle the car engine works. and how....

Answer 1

There is a good explanation here:
http://en.wikipedia.org/wiki/Internal_combustion_engine

Answer 2

car engine (petrol engine) was designed by Otto in 1876 and hence also known as Otto engine.
in it, petrol from a tank goes to a chamber (corroborator), in the form of jets. there fuel is mixed with a fixed amount of air and then this mixture is allowed into the main cylinder
the cylinder is made of steel and is fitted with a movable piston. there are two valves fixed V1 and V2. V1 is the inlet and V2 is outlet. valves are opened and closed at proper timing.
there is a spark plug in the main cylinder which produces electric spark. which burns the fuel and air mixture.
now the whole working can be described in 4 steps (strokes)
1- charging stroke - V1 opens and the piston moves down.
2- compression stroke- now both valves are closed and the piston moves up which compresses the mixture to a higher temperature(750 K) and pressure.
3-Working stroke- the spark plug produces spark and the mixture ignites. temperature increases to 2500 K and pressure up to 20 atm. thus the piston moves down which rotates the crankshaft and hence the flywheel.
this step provides a huge amount of mechanical energy
4-exhaust stroke- now the burnt gases are delivered to atmosphere by V2 and the cycle completes.