exhuast energy recovery

[George Tyler]

I found this: "Unlike a conventional turbocharger the turbine was coupled to the engine's accessory driveshaft and acted as a power recovery device. It was thought that using the turbine would lower fuel consumption allowing the engine to be used in larger transport aircraft. This was confirmed during testing"

Maybe a turbine from a turbocharger linked to the fan belt would recover waist energy from the exhaust, and thus reduce fuel consumption?

[George Tyler]

this was at:
Wapedia - Wiki: Rolls-Royce Crecy

[Odin]

I've seen experimental half steam half gas engines where the heat from the gas engine boils the water which is injected into its own special cylinder, seems to be going well last time i heard anything but then again, i never heard anything at all.

[Jim-Bob]

I remember reading about BMW experimenting with exhaust gas heat recovery a while back. I Googled it and came up with a few articles. Here's one for anyone that is interested: Green Car Congress: BMW Developing Steam Assist Drive Based on Waste Heat Recovery

Also, a more recent article (Note: Rankine Cycle is what a steam engine uses if memory serves): http://www.greencarcongress.com/2009...-20090503.html

[Joenavy85]

i can't imagine exhaust back pressure due to the turbine would be very good for FE, but that's just my $.02

[Arragonis]

The passage involved is this :

Later testing involved the use of an exhaust turbine which was a half-scale version of that used in the Whittle W.1 turbojet, the first British jet engine to fly. Unlike a conventional turbocharger the turbine was coupled to the engine's accessory driveshaft and acted as a power recovery device. It was thought that using the turbine would lower fuel consumption allowing the engine to be used in larger transport aircraft.

My reading of this is that it used a belt from a "turbine" (similar to a Turbo) to recover some power but not sure where the power went or how it was used although it seems to reduce fuel consumption somehow. Maybe it added a subtle jet to the aircraft or aided in turning the propeller. The latter seems likely as the next bit says

This was confirmed during testing however failures due to severe overheating and drive shaft fractures were experienced.

Adding a belt to a turbo which has low inertia will increase the resistance of the turbo vs. exhaust pressure - so lag will increase. This is not an issue when you are piloting a propellor plane across the Atlantic - the engine will be running for 9+ hours at a constant speed. It is an issue when you need your turbo car to complete that overtake.

A key factor in a modern turbo car is responsiveness (i.e. reducing lag). Modern turbos have variable geometry to allow this to happen but its still not instant at low revs. Adding a belt will make this worse.

There is wasted energy in a turbo though. Most turbos make more boost than is required and this released. I've wondered about this being captured and then released at lower engine speeds to offset the lag effect.

[almightybmw]

The use of TEC's on big rig engine's muffler (custom made) was tested to output nearly 1KW of power, almost enough to power the entire truck. I'll have to look for the article, but I believe that was at a down-the-road rpm, so an average of possible temperatures on the hot side. I don't know what the cold side was at, but I would assume room temperature.

I'm talking with one of my professors to see if he can help me do a simple test on my car. Measure the average exhaust temp over a period of time, and set up a bench top TEC system that mimic's the average of what my car would experience. I doubt I could get 1KW out of it, but 0.5KW would still run the engine, leaving me with a much smaller need of an alternator.

Using a similar system on a radiator could also work.

I realize this isn't the same as using a turbo for power generation, but as the article states, the turbo runs as such high rpms and temperatures it causes premature failure.

[George Tyler]

I think TEC's are the ultimate, but there are a few issues. they work on temperature difference between the 2 sides, and it is hard to get the temperature of the cold side down. Also, they have a fairly low maximum temperature, and efficiency drops off as temperature increases.you need a way to keep the cool side a close to ambient, I think engine cooling water is too hot.

[ConnClark]

IMHO the best exhaust recover system was used on the Napier Nomad



Part jet engine part diesel. It is one of the engines with the lowest bsfc ever.

Napier Nomad - Wikipedia, the free encyclopedia

[George Tyler]

interesting engine, like a turbocharged deisel but taking more energy out the exhaust than is needed for boosting inlet air pressure and returning the rest of the energy to the crank. some of the energy was the jet of exhaust though, don't think you could have that on a car! but it raises the question, could we do the same without the exhaust jet?