I know turbochargers use exhaust gas to spin them up, but that's not like trying to spin a generator. Even then, I think turbo chargers draw off some HP to spin the turbo. I understand it works to get more air into the engine for even more HP... an electric generator would be a more demanding load and likely would not give a worthwhile return.
Alternator deletes have been done on drag racing machines where batteries last long enough to do a run or 2. So it works for that. But it just wouldn't be practical for much else. Small dedicated gas generator to keep battery charged on a vehicle sans alternator may free up HP for the vehicle, but then it takes fuel to run the generator. Added complication with little to no net benefit... Back to square one again as far as I can tell.
Southeast Michigan Dark Side Rider
4 Honda Reflex scooters & a FSC600A Silverwing
Originator of the "Darkside" Honda Reflex.
"Yeah dude, that IS a car tire there on the back of my scooter."
Sometimes I'm so far outside of the box, the Hubble telescope can't find me