My argument isn't that there isn't enough energy, just not enough waste energy...
But I agree that this could be useful, it's something that should be implemented on all cars. Cars already need some kind of muffling, and accomplishing the muffling with a turbine that returns some shaft power back in the form of reduced alternator load is better than a restrictive muffler, or even an active noise cancelling system (which takes power).
I'm trying to say though, where you're going to see a potentially large increase in fuel economy is tapping waste heat. Currently, nothing is being done to capture waste heat. I believe it is the case that combustion efficiency improvements are nearing a dead end, and significant friction reduction can't happen without a fundamentally different design to the engine, so what's left to tap is waste heat. BMW's steam generation system produced double digit improvements in efficiency under some conditions, and it didn't touch the actual engine at all. Unfortunately thermoelectric generators aren't very effective and steam based systems have high weight penalty...but there's so much potential.
Glad we had a relatively civil discussion, another thread I posted in is going crazy
