Please explain why the Carnot cycle is reversible while the Otto cycle is irreversible using the kelvin or clausius statement of the second law

Question

why is the Carnot cycle reversible while the Otto cycle irreversible according to Kelvin-planck statement

Answer 1

Edit: The answer below may be misleading. See for instance this Physics SE post for a discussion of the reversible Otto cycle. Thanks to @hyportnex and @Chemomechanics for the correction.

The Carnot cycle is reversible because all heat transfer occurs between systems at equal temperature. This is not the case in the Otto cycle, which is therefore irreversible because to run it in reverse you would need heat to flow spontaneously from a colder body to a warmer body.

You may well ask "why would heat flow from one system to another if the two systems are at the same temperature?" Well, it wouldn't, and this is why the Carnot cycle is an idealization; it can't actually be realized. You could try to approach the Carnot cycle in a real-world implementation by making the temperature difference between system and reservoir during the isothermal processes infinitesimal. In the limit where the difference goes to zero, you would obtain the Carnot cycle. But note that the rate of heat transfer would also approach zero due to the vanishing temperature difference, so in this limit the time required to run through a cycle approaches infinity.