Despite claiming they could replace diesels, I don't see any real numbers other than comparisons with their own gasoline engines. For internal combustion engines, the most efficent are still two-stroke diesels, which can have thermal efficiencies of over 50%:
Seeing as this design includes several more moving parts than conventional ones, it's an open question how much reliability and longevity are affected; I remember reading in a book that over the years many have tried to make more efficient engines and succeeded in achieving that goal, only to be let down because of real-world reliability issues.
https://en.wikipedia.org/wiki/Brake_specific_fuel_consumptio...
Seeing as this design includes several more moving parts than conventional ones, it's an open question how much reliability and longevity are affected; I remember reading in a book that over the years many have tried to make more efficient engines and succeeded in achieving that goal, only to be let down because of real-world reliability issues.