According to Carnot's theorem, Carnot engine is the most efficient engine. I wanted to know its proof. I looked up and I found a proof on Khan Academy in which he used a reverse carnot engine to prove that an engine more efficient than Carnot engine cannot exist.
But my question is can there be an engine not having 2 adiabatic and 2 isothermal processes, and more efficient or equally efficient to Carnot Engine? If not, can anyone please give me an idea why having 2 isothermal and 2 adiabtic processes makes it the most efficient and why not any other series of processes?
Best Answer
Yes, there can be engines NOT having 2 adiabatic and 2 isothermal processes and still be as efficient as the Carnot engine; however, no engine can be more efficient than the Carnot engine with both of them operating between the same 2 thermal reservoirs. Your query is addressed in Carnot's 2nd postulate which says: All reversible heat engines operating between the same 2 thermal reservoirs (i.e. fixed temperatures) have the same efficiency. A nice proof of this is given in https://www.youtube.com/watch?v=5q_MMdGINgQ&list=PLA17CE108925DC94F&index=7. The proof of this postulate starts at 00:09:30 in the video.