Fuel is Fuel.... An alternative view to economy

[Bicycle Bob]

Originally Posted by mpg_numbers_guy

A very old link describes how some British engineers designed a sort of turbo generator that generates electricity from the turbo being spun by hot exhaust gases. They claimed up to 6kw of power available, although that number seems a bit stretched. Seems like a neat concept, but I see no instance of this having made it to production. The link to the original article in the site is dead.

https://www.greencarcongress.com/200..._exhaust_.html

Honda is either using, or will be using, a Rankine cycle system in their hybrids that follows a similar method by using exhaust gases to evaporate water and generate electricity through steam.

If we consider that the average ICE engine is 30% efficient, or perhaps 40% efficient if it's a lean burn Honda or Atkinson cycle car, then for every 5 hp the car generates, 7-12 hp is being wasted (5.2 - 8.9 kw).

Even if such a system is only 15% efficient, that's still around a kilowatt of power being generated. And that's at 5hp; at highway speed more power could be generated.

This electrical power could then be stored and used for a variety of purposes, from a constant electrical boost to an engine to storing the electricity in batteries for home use. This would allow a more practical use of the wasted energy than trying to use the direct heat from the exhaust - which contains many toxic chemicals and therefore shouldn't be used to heat a house or other building.

One also has to consider the cost of implementing such a system - are we talking about efficiency, or economy? There is a difference between the two. Economy has to take into consideration implementation cost.

Sorry I'm rushed these days, but the last big piston aircraft engine, the fabulous Napier Deltic, used the pistons as a gas generator, and took the propeller power off from the exhaust turbine. It got great mileage, but cost too much as jet turbine alloys improved.

[freebeard]

https://en.wikipedia.org/wiki/Napier_Deltic
I remember it more for the opposed piston layout.

Earlier attempts at designing such an engine met with the difficulty of arranging the pistons to move in the correct manner, for all three cylinders in one delta... Mr. Herbert Penwarden, a senior draughtsman with the Admiralty Engineering Laboratory, suggested that one crankshaft needed to revolve anti-clockwise to achieve the correct piston-phasing, so Napier designers produced the necessary gearing in order that one of them rotated in the opposite direction to the other two.

Turbo-compound:

Turbo-compound Deltic
The "E.185" or "Compound Deltic" turbo-compound variant was planned[1] and a single prototype was built in 1956[12] and tested in 1957.[13] This capitalised on Napier's experience with both the "Nomad" and its increasing involvement with gas turbines. It used the Deltic as the gas generator inside a gas turbine, with both a twelve-stage axial compressor and a three-stage gas turbine. Unlike the Nomad, this turbine was not mechanically coupled to the crankshaft, but merely drove the compressor. It was hoped that it would produce 6,000 horsepower,[citation needed] with fuel economy and power-to-weight ratio "second to none".[14] Predictions by the engineers closely connected with it were that connecting rod failure would be the limit on this power, failing at around 5,300 bhp. On test it actually produced 5,600 bhp before throwing a connecting rod through the crankcase just as predicted.[12] Naval interest had waned by 1958 in favour of the pure gas turbine, despite its heavier fuel consumption, and no further development was carried out.

[Ecky]

Originally Posted by richierocket

Ecky, you quoted the 40% ICE efficiency, but isn't that just the PEAK efficiency when you're riding the island on the BSFC plot? For most drivers, most of their driving is far off this peak. So the average ICE efficiency is down <20%.
People on this forum are aware of that and drive for efficiency but the vast majority of people do not. So if an electric motor is at 90% for all driving conditions, then doesn't that make more sense for majority of people?

Modern hybrids do a fantastic job of keeping engines in this range, as they can nearly entirely decouple the engine from the tires, only running it as needed and nearly always in its most efficient range.

[cRiPpLe_rOoStEr]

Originally Posted by Bicycle Bob

Sorry I'm rushed these days, but the last big piston aircraft engine, the fabulous Napier Deltic, used the pistons as a gas generator, and took the propeller power off from the exhaust turbine. It got great mileage, but cost too much as jet turbine alloys improved.

I'm aware the Napier Deltic borrowed some design features from Junkers aircraft engines, but I'm unaware of any aeronautical application for the Napier Deltic. OTOH they were great powerplants for trains and some military vessels.

[richierocket]

Originally Posted by Ecky

Modern hybrids do a fantastic job of keeping engines in this range, as they can nearly entirely decouple the engine from the tires, only running it as needed and nearly always in its most efficient range.

Ecky, yes agreed. In your original post you didn't mention hybrid, so I thought you were saying an ICE-only powered vehicle could get 40% average eff, which it can't. A modern hybrid is a great compromise all around. IMHO plug-in hybrid, even better.