Automotive Energy Recovery

Discussion on Stirling or "hot air" engines (all types)
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Joined: Mon Aug 20, 2007 9:07 am
Location: England

Automotive Energy Recovery

Post by Rufe0 » Mon Aug 20, 2007 9:21 am

Hi I'm completely new to building Stirlings
I wanted to ask for some advice on a design for a Car. What I am trying to do is generate some extra electricity for generating hydrogen through electrolysis. The ultimate goal is to run 100% Hydrogen 0% petroleum as fuel however this is almost impossible because hydrogen generation is slow and does not produce more energy than it takes to make the hydrogen in the first place. Or if it does you would have a massive engine that only produced the HP of a small engine.

So anyway my hope is to generate some 'free' energy off the exaust. I figure the exaust has both kinetic energy which would be harnessed by a turbo fan normaly and heat energy which would be harnessed by a stirling/steam engine. Running on a high percentage of hydrogen there will be alot of steam in the exaust. Hydrogen burns at 55000 degrees C (i think i heard) but normal exaust teperatures are somthing like 1000-2000 degrees.

I have done a drawing of a design that would combine the kinetic harnessing of the turbo and the heat harnessing of the stirling.
The exaust of the engine is directed into the piston of the hot side of the stirling which will 'help' it. I don't want to push it the whole way i just want to 'help' it. Then that piston will exaust to a coil sournding the Hot side of the stirling. The cold side will either actualy extrude from the bonnet of the car or will have a radiator. The cold side will have piston power but it wont be directly connected so the heat isn't trasfered to it.

So realy I just wanted to have some advice from someone who has actualy built a stirling, is this going to work well or not?

I have an even simpler design where I would have 2 Stirlings and simply inject the car exaust directly into the hot side. Then on the cold phase it would inject into the hot side of the other stirling alternatley.

Probably the easiest thing would just be to have a normal turbo fan. I could actualy make a jet engine out of it. I could use the car exaust instead of the fuel, it wouldnt be harly as powerful but still any benefit is good. This would be cheap, lightweight and compact but probably not very efficent.

Anyway let me know what you think
Cheers Adam

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Joined: Tue May 16, 2006 5:06 pm
Location: California

Post by SScandizzo » Wed Aug 22, 2007 4:47 pm

Hi Adam,

Take a look at this article from a couple of years back: It looks like reusing engine heat has been around for a while. There are two things you need to keep in mind about a Stirling engine's design (in this particular case an alpha configuration). First, the system is closed; that is, gas may neither enter nor exit. Second, the crank (presumably at the spot you marked for a generator) must be tied to both the hot and cold pistons at about a quarter cycle offset.

As soon as you use the word "valve", I begin to think more about a steam engine which uses expanded gas (steam) to move a cylinder and then discharges the gas into its environment.

Also, you will note that the BMW system only uses the heat from the engine, not the pressure created by the exhaust. Using the exhaust pressure to even "help" move a piston may cause back pressure in the IC engine making it less efficient. The reason race cars have headers (big open exhaust pipes that leave the engine) is because they reduce back pressure and maintain high exhaust temperatures. These high temperatures actually help the exhaust gases flow better, which results in a phenomenon called "scavenging". Scavenging improves the flow of combustable material in the cylinders, which in turn improves their efficiency.

Now how about a hybrid car that already utilizes electricity and produces heat from an IC? THAT might be an interesting candidate for your idea!


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Joined: Mon Aug 20, 2007 9:07 am
Location: England

Post by Rufe0 » Thu Aug 23, 2007 12:00 am

Cheers for that link that is a realy insteresting article. With 10Kw extra power you could make enough hydrogen for 10cars. I was thinking somthing like 200 or so watts would be enough.

Yes I supose you could consider my design to be like a steam engine with a stirling stuck on the front.

Thats a nice idea about headers but it might be a bit noisy...

So I think it comes down to either a normal stirling or normal steam, possibly turbo fan but I dont want togo that route. So realy im looking for 1-2Kw which is small and light, which I would think would lean it more to the steam side.

Anyone built steam or stirlings using temps around 1000-2000degree producing 1/2kw?

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