I beg your pardon. A Carnot engine is indeed a heat engine. The heat of combustion creates hot compressed gas - on which it runs by expanding that gas. A compressor is also a Carnot engine, you compress the gas and you must extract the heat from the hot gas or your air tank will fill with hot gas. As this cools, unless you can use that heat for other tasks, it is wasted. A carnot engine is not reversible. If you run it backwards you must submit to the equation and take your losses. They have been hard at work for almost 200 years trying to beat Carnot - he won them all, no survivors, but he gained immortality...

https://en.wikipedia.org/wiki/Carnot_cycle

The Carnot cycle is a theoretical ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. read the wiki for more

An internal combustion engine runs on an Otto (or maybe Atkinson) cycle, though, not a Carnot cycle. All thermodynamic cycles are heat engines, but their efficiencies aren't the same.

How do you mean a Carnot cycle isn't reversible? You can run the cycle in either direction. That's not the same as saying is has 100% efficiency.

The Otto cycle means the Otto mechanical sequence. Reversible means run it backwards and it returns the burned gasses etc to fresh fuel, heat etc. etc with 100% recovery

They are referring to an internal combustion engine as a device that coverts heat/expanding gas->work, where the reverse is work->heat/compressed air.