Exhaust Heat Recovery - Steam Power

[jdgFirefly]

I was serious about using an air conditioning system it is basically the same cycle, with most of the main components of the steam cycle. The parts are available in various sizes at your local salvage yard.

You don't need a turbine to make steam power. Its always been more difficult to manufacture a turbine than a piston motor of the same eff. So i think your more likely succeed with a seam piston rather than a built from scratch DIY turbine. Piston pumps and motors are easy to come by so you have a large selection of sizes and arrangements to chose from. Another option could be to modified air tools. There typically not piston but they are positive displacement (vane motor).

I think that having a positive displacement motor is important in this situation because it is less sensitive to varying loads and will work with a wide range of input pressures. Whereas a turbine needs to be designed for specific operating parameters (not DIY friendly).

What ever you decide I hope it works out for you. Heat recovery is really the last place for big gains in engine eff.

[Daox]

Originally Posted by 320touring

the alternators fitted to the e30 have a sort of fanblade/waterwheel setup on the pulley driven by the belt-could that be modded to produce something similar to the hole solution you've suggested?

Not a bad idea, but I imagine that is there for cooling. If I use it for a turbine, I'm not only stealing that cooling capacity, I'm heating it up! I imagine that ending in a bad way.

Also what consideration haave you given to rusting to the exhaust?

Almost none at this point. Most exhausts are stainless so IMO its not a huge deal. Of course heat transfer through SS is pretty bad, so that is a concern.

Its a great idea, but what effect will the additional sleeve on drag under the car if it hangs lower than the rest of the exhaust, or do you envisage using the setup on the downpipe or manifold?

I don't know where I'd place it yet. Obviously the closer to the engine the more available power and less need to insulate the exhaust. In the environmental aspect of it, you'd not want to rob heat from the CAT though.

[Daox]

Originally Posted by jdgFirefly

I was serious about using an air conditioning system it is basically the same cycle, with most of the main components of the steam cycle. The parts are available in various sizes at your local salvage yard.

You don't need a turbine to make steam power. Its always been more difficult to manufacture a turbine than a piston motor of the same eff. So i think your more likely succeed with a seam piston rather than a built from scratch DIY turbine. Piston pumps and motors are easy to come by so you have a large selection of sizes and arrangements to chose from. Another option could be to modified air tools. There typically not piston but they are positive displacement (vane motor).

I think that having a positive displacement motor is important in this situation because it is less sensitive to varying loads and will work with a wide range of input pressures. Whereas a turbine needs to be designed for specific operating parameters (not DIY friendly).

What ever you decide I hope it works out for you. Heat recovery is really the last place for big gains in engine eff.

Modified air tools, that sounds like a great idea! Just wonder if they can take the heat... I'm not even sure how hot its really gonna get to be honest. I can't imagine there are too many plastic bits inside air tools. Anyone know? I'm thinking a die grinder would be easy to adapt.

[RobertSmalls]

Here's a drawing of an easy to build impulse turbine. The efficiency isn't great, but that's fine for now.

The alternator wants to spin at 3000-15000 RPM. Alternators are cheap. As long as it doesn't grenade every time you turn off the car, it should be fine without an overspeed brake. Getting it to spin fast enough under load might be an issue, though.

If you determine you need more heat exchanger performance, you many need to go for a bunch of copper tubes inside a 3" diameter exhaust pipe. Actually, I have a book with a chapter or two on analysis of heat exchanger performance, or you may be able to find a concentric tube-in-tube heat exchanger simulator online. But you'll need to know the inlet temperatures of the working fluids and the desired heat flux.

[320touring]

Originally Posted by Daox

Not a bad idea, but I imagine that is there for cooling. If I use it for a turbine, I'm not only stealing that cooling capacity, I'm heating it up! I imagine that ending in a bad way.



Almost none at this point. Most exhausts are stainless so IMO its not a huge deal. Of course heat transfer through SS is pretty bad, so that is a concern.




I don't know where I'd place it yet. Obviously the closer to the engine the more available power and less need to insulate the exhaust. In the environmental aspect of it, you'd not want to rob heat from the CAT though.

i was meaning extend the shaft, than put another one on, and drive that?that way original one still cools the alt?

Could you not route a pipe inside the exhaust to heat the water?
I see what you say about the cat, just depends how much water you want to heat?

[Wonderboy]

I like the air tools idea.... any plastic parts may be able to be replaced with fab'd metal. Air tools seem like a great idea for any kind of DIY source for pistons.

[jdgFirefly]

In the past I've taken apart a die grinder and an air drill, both were all metal except for the vanes which appeared to be graphite so heat shouldn't be a problem.

Also if you have a closed system you could run it at lower than atmospheric pressure so that the water (or whatever) boils at lower temperatures.

[Daox]

Great news on the air tool materials. Thanks.

I'm not sure how you'd run a closed system. Could you post up a diagram?

[Patrick]

Air tool vanes are a plastic composite. They are cooled by the expansion of the compressed air and you have to add lubricating oil periodically or they will seize up. The tools also run at very high rpms, so some sort of gearbox would probably be needed.

[talldudenumber5]

what about running copper tubing around the exhaust pipe then to a small turbine that could generate electricity. it would be very cheap and easy enough for any one to do and you could do more than one system since exhaust pipe are generally fairly long. you could have one for your alternator delete and another to add power to the hybrid system.just an idea