# Any real heat engines based on the Carnot cycle? (or an equally efficient cycle)

Most practical heat engines are based on ideal cycles whose processes are different from the Carnot cycle (eg; constant pressure or constant volume heat addition instead of isothermal). I understand that achieving the controlled isothermal processes required by the Carnot is impractical. However, are there any real heat engines use the Carnot cycle as their basis? I'm looking to understand any implementations that do exist and why they fall short of more typically used cycles. (I do know of Stirling and Ericsson engines which are based on equally efficient cycles, but these suffer from low specific power?) Any links to papers or other resources would be much appreciated!

Alternatively, more info on why heat engines are never/rarely based on these 'optimal' cycles would be useful too! It seems counterintuitive to me that, when irreversibilities are taken into account, the efficiency of a 'less optimal' cycle would exceed that of any engine based on an 'optimum'/Carnot one

• The Carnot cycle is efficient because it is (infinitely)slow, and hence (zero) low power for a given size. Real life engines have requirements for power to weight ratio and so on, so efficiency is sacrificed for practical requirements. Commented Dec 3, 2023 at 23:39

The Carnot cycle is a theoretical cycle and, as such, no practical exngine exists based on this cycle.

This is one of the many reasons that this cycle is used to compare real or practical engines for efficiency.

You might benefit by doing a search for:

Brayton or Joule Cycle

Reversed Joule cycle

and furthering your research around cycles.

In the Carnot cycle, there are no loss mechanisms and no temperature gradients anywhere. Commonly-used thermodynamic heat engine cycles are intended as real-world approximations of the Carnot cycle, subject to losses like conductive leakage and imperfections like temperature gradients that are not included in the (theoretical and lossless) Carnot formulation which are consequences of the particular cycle (Otto, Brayton, Sterling, etc.).

There is a project for a heat engine based on Carnot cycle here :