[SaabJohan]

Turbocompound is currently in serial production in heavy trucks and have been around since the world war 2 when it was used in airplane engines.

The powerloss from the restriction caused by the turbine is almost zero while the turbine will develope a few percent of the total engine power. Since the turbine can extract quite much power I would not recommend that it's used to power an alternator, the output is also load dependant which means at idle the output is almost zero and the car will need another alternator anyway.

Any type of thrust engines is not suitable for cars as they give a high fuel consumption. As for turboshafts, the land veichle and helicopter engines are about as efficient as an otto engine, around 30%, with an increasing efficiency with increased combustion temperature. If the compressor outlet temperature is equal to the turbine outlet temperature it's 50% efficient, the rest is used to power the compressor, which means that a gas turbine engine is very dependant on the efficiencies of it's compressor and turbine and can easily drop in efficiency. The larger gas turbines used in for example ships are usually 40-45% efficient, which is lower than for a diesel piston engine, the engines are however much smaller and lighter for a given power so they are used where performance is important.