what is the principle on which cycle work ?
Answers
it doesn't have a “working principle.” It consists of four processes: isentropic compression, isothermal heat addition, isentropic expansion, and isothermal heat rejection.
The way you get mechanical work from thermal energy is to allow thermal energy to go from a hotter place to a colder place. For example, in an internal combustion engine (ICE), the fuel/air mixture is ignited when the piston is at the top of the cylinder. The result is a hot, high pressure gas. This is the hot place. The gas pushes the piston down, doing work, expanding, cooling and dropping in pressure. When the piston reaches the bottom of the stroke, the gas mixture is cooler. This is the cool place. Then the exhaust valve is open and the gas exits to an even colder place (the atmosphere). But, that escaping gas still had some usable energy in it that was wasted. As a result, entropy increased.
The Carnot cycle is a way of operating a piston in a cylinder without releasing the working gas to the environment. The operating gas is heated and cooled, but never released. The Carnot cylinder and piston extract mechanical energy from thermal energy without increasing entropy. You cannot do better than a zero change in entropy, so an engine based of the Carnot cycle would be the most efficient at using thermal energy. Of course you can still be wasteful in the way that you generate thermal energy.