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
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.