Turbo compound diesel.
 

It is an old idea but it is being done again. I think Cat is doing one too.

https://www.detroitdiesel.com/engines/dd15/economy.aspx

An extra turbine feeding up to 50 Hp back into the crankshaft.

I didn't see details on the means of transferring the turbocharger's output into the "50 added horsepower".
Is this through a second turbocharger further compressing the intake air to allow more fuel?
Or is this a mechanical connection in which the second turbine's shaft is directly and mechanically linked to the ICE's rotating members ("back into the crankshaft")?

Compound turbochargers (plumbed in series) have been used right along. There's a VW Jetta TDI running around Merrimac, NH with twin sequential turbos. Able to produce close to 40 lb of boost, but limited at the moment to 30 due to still having the stock 19.5:1 compression.

If the Daimler / Detroit Weasel is mechanically linking the second shaft to the rotating components, then THAT's something new.

They do mechanically couple the exhaust turbine to the flywheel. It's in their brochure.

https://www.detroitdiesel.com/pdf/eng...5-brochure.pdf

Indeed all things old are new again. Turbocompounding was popular in big piston aircraft engines at the dawn of the jet age. The Napier Sabre engine ? turbocompounded gas engine ? was reputed to be the most efficient gas engine ever built. The very high efficiency of the R-3380 made the enormous range of the B-29 possible. Both were maintenance hogs.

Turbocompounding is a wonderful idea for engines that operate at constant speeds ? boats, aircraft, and to a lesser extent trains and trucks. For a private car or truck it isn?t worth a hoot. Turbocompounding requires a high gas flow to work. Most of us do our dead level best to minimize gas flow. With little gas flow, there is little energy to be harvested. If it were me, I might have a second turbine to run the accessories (alternator, air conditioning, power steering/brakes, etc) Also, diesels are very efficient as is. There is not much energy left in that exhaust gas if your engine is smaller than 14 liters and run at less than a line-haul duty cycle.

For most of us, it would be as useless as the four-wheel drive equipment in a suburban SUV.

I've come up with a modified version of this device. I'm finally wrapping up the process of researching (I started in September) and I'm just now starting the process of collecting parts to see if this will work or not. Hopefully in a few months I'll have a small functioning model! If I can get it to recoup 5 - 10 hp then I'll be jumping for joy!! The main goal is to only add a VERY small amount of backpressure, or idealy add no more backpressure than what a gas/diesel vehicle has stock.