Exhaust Heat Recovery - Steam Power

[Christ]

^^^ I was just thinking that looks an awful lot like an oil pump...

Thanks for the heads up on the steam thing. I should have known that, but apparently it slipped me while I was attempting to think. That's why there's more than just me here!

[bschloop]

I have considered using an ac compressor in reverse as an engine, and it does turn quite well when hooked up to compressed air. It will only turn in one direction though.

[jdgFirefly]

Originally Posted by bschloop

I have considered using an ac compressor in reverse as an engine, and it does turn quite well when hooked up to compressed air. It will only turn in one direction though.

Interesting, have any more information for us? Did you actually connect it to a load or was it just free spinning, what pressure did you test it at? Did you actually turn on into an engine.

Gerotors are cool. They are another form of positive displacement pump/motor but I haven't seen them in larger applications vary often, I'm not sure what the advantages/disadvantages are over other pumps. I think the reason you usually see them in smaller applications is because the ring gear part spins with the rotor which adds a lot of spinning weight, otherwise the
rotor must orbit around the ring gear thing (think its called a scroll?). Actually a rotary engine is basically a 3 lobe gerotor with a fixed "scroll" and a orbiting rotor. Anyways I think a gerotor pump/motor could work if you can find a complete unit that's large enough for this application.

[ShadeTreeMech]

a thought just occured to me concerning removing heat from the exhaust.

I don't claim to understand all of it, but while reading up on backpressure in exhaust systems, I read a somewhat technical article concerning the need to keep the exhaust as hot as possible to facilitate it moving down the pipe as efficiently as possible. To that end, some car makers will insulate the exhaust piping to keep it warm. I'm all for getting "free energy", but I am concerned about the cost of cooling the exhaust.

[Daox]

Wooo, another great looking idea! I imagine I can pull the oil pump off the same engine I pulled that alternator off... Anyone know how fast oil pumps in car spin?

Also, I'll be on vacation till Wednesday so its not gonna get done real soon. If anyone has something laying around and wants to test it out that would be awesome!

I was also thinking... A closed system sounds a bit complicated with a high pressure pump. BUT, so you don't have to carry a ton of water, I was thinking of a semi closed system. Basically, you have the heating side and a condensing side. All the water gets collected in the condensing side after going through the turbine/pump/gerotor so you don't waste all that water (which should be distilled so there isn't build up). Now, you just dump the condensed water back to the heating side once its cooled down. You could do this manually or you could use a small cheap pump to do the same thing (windshield washer pump perhaps). You could have it run a few seconds before you start the car up. Simple and cheap! You could even throw an arduino on it with a temp sensor to automatically pump when it has cooled down if you wanted to automate it.

[RobertSmalls]

Originally Posted by Daox

Wooo, another great looking idea! I imagine I can pull the oil pump off the same engine I pulled that alternator off... Anyone know how fast oil pumps in car spin?

The off-center lobe the drives the gerotor spins just as fast as the crankshaft, because it usually is the crankshaft. They're low volume, high viscosity, fairly high pressure pumps. The low volume part may be an impediment.

You actually want the water that hits your exhaust heat exchanger to be as hot as possible. Instead of waiting for the water to cool, better to insulate it.

[jdgFirefly]

Originally Posted by ShadeTreeMech

a thought just occured to me concerning removing heat from the exhaust.

I don't claim to understand all of it, but while reading up on backpressure in exhaust systems, I read a somewhat technical article concerning the need to keep the exhaust as hot as possible to facilitate it moving down the pipe as efficiently as possible. To that end, some car makers will insulate the exhaust piping to keep it warm. I'm all for getting "free energy", but I am concerned about the cost of cooling the exhaust.

You are right about that. However about a third of the heat produced in your engine goes out the exhaust so the potential for gaining back that preformance loss is huge. Plus the preformance loss of cool exhaust vs hot exhaust is marginal in my opinion, I don't have anything to back that clam though. Also how much the exhaust is cooled will depend on how much we take for power and how eff the system is, So its not like the exhaust will be ambient temperature. The exhaust temp can be no less than the temp of the boiler otherwise there will be no heat transfer.

I suppose if it becomes a problem you could put the boiler at the end of the exhaust pipe to mitigated the losses due to cooler exhaust.

[jdgFirefly]

Originally Posted by Daox

Wooo, another great looking idea! I imagine I can pull the oil pump off the same engine I pulled that alternator off... Anyone know how fast oil pumps in car spin?

Also, I'll be on vacation till Wednesday so its not gonna get done real soon. If anyone has something laying around and wants to test it out that would be awesome!

I was also thinking... A closed system sounds a bit complicated with a high pressure pump. BUT, so you don't have to carry a ton of water, I was thinking of a semi closed system. Basically, you have the heating side and a condensing side. All the water gets collected in the condensing side after going through the turbine/pump/gerotor so you don't waste all that water (which should be distilled so there isn't build up). Now, you just dump the condensed water back to the heating side once its cooled down. You could do this manually or you could use a small cheap pump to do the same thing (windshield washer pump perhaps). You could have it run a few seconds before you start the car up. Simple and cheap! You could even throw an arduino on it with a temp sensor to automatically pump when it has cooled down if you wanted to automate it.

If you already have bulky condenser and storage tank plus all the plumbing you might as well add the pump and make it a closed system.
So I'm kinda a closed system pusher. Some of the reasons I like the idea are:

- No maintenance or consumables
- lubricant can be added to the loop to solve the lubrication problem.
- possibility for lower than ambient pressures at start up.
- This will lower the boiling point which may allow power production at lower exhaust temps and therefore power production at start up.
- Lower boiling point will allow you to experiment with recovering the waste heat in the cooling system and greatly increase the potential power producing capacity.
- The lower boiling temp may allow for refrigerants to be used rather than water, no freezing and designed to lubricate the system.
- An a/c is already a closed system so it may be just a matter of plumbing the right parts together with off the shelf fittings and junk yard components, and if we can figure out how to do this I could see lots of ecomoders converting there a/c into a generators.

You are right though it is more complicated that a open system. If you do go the open system idea don't bother with the condenser and just embrace the simplicity. It may be a pain adding water but it will be more simple and a good proof of concept project. It is better to start with a simple setup and succeed that to try for the Ideal setup and fail.

[Baggage Handler #2]

Originally Posted by ShadeTreeMech

a thought just occured to me concerning removing heat from the exhaust.

I don't claim to understand all of it, but while reading up on backpressure in exhaust systems, I read a somewhat technical article concerning the need to keep the exhaust as hot as possible to facilitate it moving down the pipe as efficiently as possible. To that end, some car makers will insulate the exhaust piping to keep it warm. I'm all for getting "free energy", but I am concerned about the cost of cooling the exhaust.

I haven't really given it a thorough "think," but if my recollection of the relationships between pressure, volume, and temperature is correct, if you can reduce the temperature of the exhaust as it travels along the tailpipe without introducing a restriction, the pressure ought to be reduced as well. If we lower the temperature (and therefore pressure) more or less linearly between the muffler and the outlet, the exhaust flow ought to improve rather than otherwise. Maybe think of it as creating a partial vacuum at the exhaust tip.

Good thing to be aware of though.

[jdgFirefly]

I just went to the junk yard to look a a/c compressors. I took apart two, both swash plate piston style. Both didn't have a rotating orifice plate, only reed valves which do not allow the pump to run as a motor. I looked at a lot of different cars but all seemed to have the same style of compressor, at least they look the same from the outside, nothing that looked like it could be a scroll compressor.

One exception was the compressors found on the older chev caprice, it had a more pancake shaped compressor. I could see into the compressor form the intake port and it looked like a radial piston setup. I covered one port with my thumb and turned the shaft both direction. It produced pressure from the same port regardless the the direction the shaft turned so this suggested to me that it also had reed valves.

from this trip it seems that auto a/c compressors are a dead end. Unless someone knows of one from a specific car model.

bschloop you said you were able to turn a compressor with compressed air. What type of compressor? And what was it out of.

just as a side note the first unit i looked at had about 1" dia pistons with 1" stroke X10 which works out to 128cc displacement. A lot bigger than i thought it would be.