How does petrol engine works?

The petrol engine was made by Otto in 1876. It consists of the two valves inlet and outlet valves. As it was manufactured  by Otto it is also known as Otto engine. It performs the work by following four steps they are
1. Charging stroke:During this phase the inlet valve is opened due to which the vapors of petrol and air is sucked by pulling the piston downward. This is the first phase for the working of the petrol engine.
2. Compression stroke: This is the second phase for the working of the petrol engine. During this condition the piston is move upward and in such a way that the volume is reached to one fifth of the original volume and the temperature reaches 600 degree Celsius and the pressure to 7 atm so in this end process a series of the spark is produced at the end of this process.
3. Working stroke: After the production of spark of fire now the temperature reaches to 2000 degree Celsius and the pressure to 15 atm due to which here in this phase  the engine works.
4. Exhaustion stroke: this is the final phase of the engine which is very easy to conduct by opening the outlet valve. Due to this region the harmful wasted and vapours are removed out in this phase.
     
        Hence in this way the petrol engine works on the four phases not only this but also it is lighter in weight and also is suitable for the run of the small vehicles.