Aircraft engines had an "simpler solution" to this problem, they geared the output of the turbo charger down to the crankshaft speed and directly recovered the

Aircraft engines had an "simpler solution" to this problem, they geared the output of the turbo charger down to the crankshaft speed and directly recovered the power into mechanical energy. This was known as a turbo compound engine: https://en.wikipedia.org/wiki/Turbo-compound_engine https://en.wikipedia.org/wiki/Turbo-compound_engine These improved fuel efficiency by 15-35%. It's actually the reason my mind jumped to recovering energy from exhaust gasses. Doing this directly from heat would be elegant if it could ever be made cost effective.