Recover waste heat from exhaust

[ejin4499]

So I was noodling around the net and ran across an idea of recovering heat from the exhaust using the rankine cycle. I though that was a great idea as then you could reduce the load put on your alternator and by extension your engine and then run more accessories from the battery. My next thought was if we are recoverying truly wasted heat you could then run a hydrogen generator to further improve efficency.

 

Anyone have any ideas on what it would take to make that work?

 

So I found someone making a small turbine.

http://www.infinityt...it_Version.html

this one is only about three inches long but they also make one a little larger.

 

Does anyone know how much pressure the stock cooler for the auto trans is rated for?

My thought was (since I swaped to manual and still have the stock cooler) run copper tubing around the exhaust to heat it then run it through the turbine then use the stock transmission cooler to condense the steam back to liquid again gravity feeds back to the copper tubing. repeat.

[Slartibartfast]

My first thought is, this is what a turbo does. It uses air flow, but as the air expands it cools... so it's much cooler coming out than it was going in.

 

I'd be interested to see just how much juice you could get from a hot exhaust... and whether that would be worth the additional stuff. Internal combustion does throw away a whole lot of heat...

 

Maybe there's a way to tap into the engine coolant? It's already set up to get up as much heat as possible... of course, the antifreeze would hamper it steaming up, but as anyone who's pulled the rad cap on a hot engine knows... it'll still make steam. If you pulled pressure from it where it leaves the engine, that's probably its hottest point.

 

I'm still skeptical on the whole hydrogen thing... seems like a whole lot of extra stuff to lug around.

Edited May 24, 2012 by Slartibartfast

[unccpathfinder]

I don't think you will hit the pressure or flow #'s...start reading up on thermodynamics and back out the theoretical efficiencies and if its worth the time or $

[ejin4499]

I don't think you will hit the pressure or flow #'s...start reading up on thermodynamics and back out the theoretical efficiencies and if its worth the time or $

 

The required minimum to make that particular steam turbine turn a generator is 25 PSI. Assuming I wanted 50 psi I would need to get the water 280 F. Thats assuming I was using water I could use a refrigerant that would make better pressure under lower temps. But as you said I probably need to read up on thermodynamics. The manufacturer has some tables on the site linked for required speeds psi and cfm. Its all using compressed air as the motive force so I'm sure steam or refridgerant would be different. looking at those numbers and the heat requirement I think we should be able to make a decent amount of juice espcially considering that this thing is only the size of your hand.

 

60 psi

25 cfm

6,880 rpm

32.4 VDC 37.5 A

[unccpathfinder]

So what are you using to compress the liquid and create flow? The problem is there's no such thing as a 100% efficient system...most cycles are 30-50% efficient...yes geothermal type systems are energy conservers but cannot be used to create more energy than what was there originally.

 

Energy in = energy out...meaning its heat, mechanical power etc and so forth...

[Tungsten]

I don't know about waste heat and exhaust. The exhaust needs to be hot for the catalytic converter to work properly and for the exhaust gasses to exit faster and scavenge better. Internal combustion engines are just very inefficient in general. If you want to start recovering waste heat, try starting with the radiator first. A good amount of energy is always lost through the radiator.

[tmoore4512]

This thread reminds me of the brown gas guys, and their quest for better fuel mileage running the additional hydrogen element....

[ejin4499]

This thread reminds me of the brown gas guys, and their quest for better fuel mileage running the additional hydrogen element....

 

The browns gas guys aren't entirly incorrect. The hydrogen oxygen mix does make the combuston in the chamber faster and more energetic. To get anything from it though you need to tune your managment system to be able to account for it, but I doubt that that extra efficiency overcomes the energy loss from the engine and the alternator. If your going to makes browns gas on the vehicle you need to get the initial energy from somewhere other than the turning of the motor. The only difference is where I propose to get the energy to split the water from. They are choosing to get it from the alternator. I am electing to try and get it from the waste heat running out of the tail pipe (after the cat would be the hotest) and from the radiator. If I can get my hands on a reasonbly priced turbine I can start testing.

 

Even without the browns gas just running the extra power to the battery and switching to an e-fan should save you somthing in mileage. You could go really nuts and try to run your ac and power steering off of it too. Though I doubt a little turbine like I posted about would make enough power to run the electric motors that would be required for that.

Edited May 25, 2012 by ejin4499

[Slartibartfast]

Turbines are fast, but I can't imagine them developing the kind of torque to run a compressor or power steering. Seems like minor electrical generation/running the dome light would be about it.

 

But I'd love to see what you come up with.

[ejin4499]

Turbines are fast, but I can't imagine them developing the kind of torque to run a compressor or power steering. Seems like minor electrical generation/running the dome light would be about it.

 

But I'd love to see what you come up with.

I must missunderstand you because turbines are what generates all the electricty in the US. Wether its coal nuke or oil it all heats up water and turns a turbine. The Hoover damn uses all that water pressure to turn turbines. In the OP the company that makes that particular turbine is for the purposes of energy generation from waste heat from deisel generators or other industrial processes.

Edited May 28, 2012 by ejin4499

[ejin4499]

So what are you using to compress the liquid and create flow?

 

I was thinking of a pump with a one way valve as a backstop. The problem with this is it would lead to an energy production rate like a sine wave when I wan't something nice and smooth.

My other thought was (for the proto-type) using the air conditioning pump that is already rated for use with r134 and I think would have the power to keep the pressure in the system constant. Need to do a little research on how much pressure is maintainted in those systems. I need to do a little math to figure out if I would recover enough energy from the exhaust to cover the cost of running the ac pump like that. It's just an idea I had while in the shower.