Sterling Engine to Power Alternator?

[The A Body]

Ok, reading some of the posts on disconnecting your alternator to gain about 10% in fuel economy got me thinking. Obviously, that really only works if you're going to commute around town. Any highway driving is out of the question. But of course, for those of us who do drive on the highway alot, we'd love to have 10% better as a constant. So basically, you've got a ton of waste heat coming off your engine block and exhaust manifolds that isn't going anywhere except out the tailpipe. So, I pose the following:
Has anyone else thought of building a sterling engine or small water boiler to specifically run your alternator on?
I realize that is going to take up some decent space in your engine compartment. But, in my case, I have a 1968 Pontiac Lemans with the OHC 6 SPRINT and enough space to sit in my engine bay and change anything I want. Needless to say, I've got more then enough room.
It's just a thought, but I wanted to know what some of you guys thought about it.

~The A Body

[theholycow]

See this post: http://www.gassavers.org/showthread.php?t=7633

[liqfuel]

wy not just a steam engine. maybe 1 HP around $1200
less money than a sterling of similar size
another radiator boiler pump, etc
porcupine boiler in the exhaust system
should be more than enough heat

beginning to think hybrid
,more bigger engine, better use of electricity

[R.I.D.E.]

BMW claims they are using exhaust heat to generate steam to drive all the accessories.

Estimate 15% increase in FE.

regards
gary

[Tyeo098]

Or a peltier?
That will convert the heat directly to electricity!

[fumesucker]

It's doable, but not easy and probably not cheap either..

BTW, it's "stirling" not "sterling"..

I've played with peltier chips enough to know they're probably not a solution. I built a cooled astronomical CCD camera with them about ten years ago and they can be finicky beasts, you have to get rid of a *lot* of heat for a little cooling and I strongly suspect they are the same way working in reverse..

[GasSavers_RoadWarrior]

I was looking at peltier elements, seemed like an easy way to get juice out... the numbers I ran made it look less than practical however, need a LOT of them to push enough volts and amps to be worth it, and at $30 a piece it adds up real quick. So bottom line there is, you can make yourself a $3000 alternator replacement, which might have parts of it burning out every week, so you'd have to save a heck of a lot of gas to pay it off. If your 10% saving meant as much as 5 gallons a week at $5 a gallon, it would take 10 years. If you're only using 10 gallons a week, then it would be a 50 year payoff.

I looked at building a thermocouple based unit from scratch, figuring larger junctions and "bars" rather than tiny wires would make for something more robust and unlikely to burn out... seems you'd end up with something the size of a couple of 5 gallon buckets and weighing 100lb+ that you'd have to try and hide somewhere under the car. Starting from scratch with a car, you could probably engineer something like this into the car, with a shaped expansion duct for the cooling fins that also provided a minor amount of thrust. Retrofitting it would be a huge PITA

Looks a lot better if you can build a thermo-mechanical device yourself for $100 or less though.

Wherever you pull the heat from though, should expand the volume of the exhaust, so as not to rob velocity from further up, otherwise you'll lose your gains with restricting the extraction and scavenging. i.e. if you've got a 2" exhaust, and you want to wrap it with copper pipe to draw heat into a working fluid, what you should do is make about a 2 foot long expansion cone, going from 2" to 3", and wrap the lines around that... reverse flow of course... put that right after the cat, and put a 3" muffler and piping on the back end...

The ghetto version would be to get these adaptors, a 2-2.25 a 2.25-2.5 and a 2.5-3.0 and weld them all together, possibly with short lengths between them if it ends up too short. Then wrap your coolant pipe around that.

[theholycow]

Hmm...I was wondering what the consequences could be from cooling the exhaust. However, I don't see how it would expand. Wouldn't it contract?

[GasSavers_Erik]

It would contract and slow down and more water would condense in the exhaust pipes

[GasSavers_RoadWarrior]

It contracts a bit and slows down a lot, therefore to keep the same mass flow rate you need a larger pipe area.