...and combustion engines in the future "could be" 3.5 times more efficient than they are now, as well.
How efficient are current wave disk engines? Any claim about a future, non-existent engine is just hot air. (In fact, the current wave disk engines probably generate way too much hot air already, or their current efficiency would be featured more prominently in the article.)
For every cycle and construction, there is theoretical efficiency limit inherent to it. Implementations will approach that, more or less asymptotically, but can't exceed.
A novel cycle and construction may leave more headroom for improvement, even if first implementation aren't particularly efficient.
IIRC turbines are usually highly efficient, but only in a narrow band, near maximum output; at low RPM they literally suck. Perhaps a novel construction could widen the gap considerably.
That's correct , but its possible that the time has come when narrow-band-efficiency is an appropriate technology.
A "typical" car with a piston engine directly mechanically connected to the wheels needs an engine with a wide rpm and power output range.
A hybrid electric drivetrain doesn't necessarily need that - if a motor that could run at 60% efficiency but only at 8725 +- 15 rpm existed, it'd be useless for a traditional car, but it'd be easy to integrate that into a hybrid electric vehicle...
How efficient are current wave disk engines? Any claim about a future, non-existent engine is just hot air. (In fact, the current wave disk engines probably generate way too much hot air already, or their current efficiency would be featured more prominently in the article.)