This recycling feature boosts the engine's efficiency to a whopping 50 percent. For comparison, a standard internal combustion engine operates only at 14 percent efficiency.
I don't know what a "standard internal combustion engine" is, but 14% is absurdly low. Maybe a Ford Model T would be around there? A glance at
https://en.wikipedia.org/wiki/Specific_fuel_consumption_(sha...
shows efficiencies of ~30% for typical gasoline engines of the automotive type (which agrees with what I remember when I studied this stuff), and closer to 50% for large two-stroke diesels.