Hello there, I just popped by because i suspect that this fabulous community would be the best place to get a theoretical question answered. (even though i suspect some of you wont like the indented role of the rotary in this context)

TL : DR version: Could you make a what would basically be a small displacement Renisis that is heavily turbocharged, run very efficient at a specific RPM? How would a diesel version compare to a gasoline one? (Maybe a single rotor would be sufficient for this application)

Long story: electric motors are awesome, but battery energy density is not even close by a long shot. So if you want range you are loosing out sooner or later to combustion. So there is some merit to using a combustion engine in combination with electric motors (like the audi E-tron) but rather than using a really small motor you have a slightly bigger one and less batteries, basically the engine should be scaled for the average energy output from you drive train (for example during an endurance race)

Wankels are not really famous for fuel efficiency but if I have understood it correctly that is more down to lowered efficiency in certain parts of the rev range. Ad in some extreme turbo charging and it might be quite good. I know the Mazda 787B got some good mileage while working high in the rev range. And this engine in a generator application would have the luxury of being optimized for efficiency at a specific RPM.

Would such an engine be able to get comparable fuel efficiency to other combustion engine choices with the same output. I know it would be smaller lighter and less mechanically complex. But can it compete in efficiency? And would the drive train solution in whole be decent considering the conversion losses from the wankel generator to the electric engines?