Explain heat engines and their working.

(N/A) heat engine is a device that causes a system to undergo a cyclic process,resulting in the conversion of heat into work.
$A$ simple heat engine is shown in the figure. The gas enclosed in a cylinder with a piston receives heat from a burner. Upon absorbing heat energy,the gas expands and pushes the piston upwards,causing the wheel to rotate.
To maintain the rotation of the wheel,an arrangement is necessary in the heat engine so that the piston can move up and down continuously.
The gas is called the working substance of the engine. The mechanism of converting heat into work varies for different heat engines.
Heat engines are of two types:
$(i)$ External combustion engines,such as steam engines.
$(ii)$ Internal combustion engines,such as diesel,petrol,and gas engines.