Stirling Heat Engine

[WXYZCIENCE]

Hello All:
It has been a while since I posted anything. Here is a neat project that I have been working on and it works real good.
A Stirling Heat Engine, while it runs on propane it would be easy to use other fuels.

Here is a picture of the re-generator

Enjoy,Joseph

[BigBreaker]

Awesome!  What is the approximate HP on that thing?  What is the working gas and pressure?  What is the operating temperature on the hot and cold sides?  What materials / parts did you use to make it?

[WXYZCIENCE]

BigBreaker, Thanks for you interest.
I can't rate this Stirling Engine in horse power but rather in watts, not many of them either. Most of my work on this unit was with the re-generator and how
it can be made to be efficient. I run the heat for 2 minutes and the engine warms up and runs at approximately 120 rpm (operating fluid helium ).
At this point I shut down the heat and the unit runs for 15 minutes. The power or heat transfer is what I am after. The power piston can not take high pressure so the piston runs at atmospheric pressure and vacuum. The Engine has a water cooled jacket and heats 2 gallons of water to 120 F in the 15 minutes that it runs. Joseph       

[WXYZCIENCE]

BigBreaker,
 Most of the material is recycled exercise bicycles and tread mills.( I could not find a better use for those things). Automotive drive shafts make up the
re-generator chamber and water jacket. The re-generator uses stainless steal scrubbers bought at the grocery store.  I tried steal but it was to fine.
The air could not pass through the steal scrubbers. On your other question the temperature of the hot side is ~ 500 F and the cold 10 F.  Joseph 

[JW]

The re-generator uses stainless steal scrubbers bought at the grocery store.

I was looking at that. I thought you may be using lathe turnings/scrap.

All in all, very impressive project. Its great to see things like this being built... Keep us posted. : )

JW

[BigBreaker]

I did a lot of reading on stirling engines.  I came away with a few key things.

The first was that the regenerator is super important and largely voodoo.  I say that because it needs high heat transfer, high flow and high heat capacity.  The high heat capacity isn't so hard but the high flow and high heat transfer really works against each other.  You want some turbulence to mix and break up the surface boundary layers but not so much that it creates too much drag.  Your scrubbers look very similar to some that I have seen from university researchers.  I would not use stainless steel scrubbers though - they have terrible heat transfer characteristics.  You can buy copper wool (more like ribbon) scrubbers that would be better.

The second was that atmospheric working fluids are not useful.  I hate to be so blunt but you need tens of atmospheres to transfer a meaningful amount of heat with a practical sized engine.  Your mechanics are awesome but atmospheric pressures mean that the heat can't go anywhere and I think that is why it will continue cycling 15 minutes after the heat source is removed.  That is mechanically amazing but thermodynamically a disaster.  Please consider boosting your pressure.  It totally changes the workings of the engine...  higher RPM. higher power, higher regenerator capacity required - but your regenerator looks GREAT.  Please use all that capacity with a denser fluid :^)

High pressure and high heat is a materials problem on the high temp side.  Testing is dangerous and destructive.  Maybe bake out some motor oil of all volatiles in your pressure vessel with it open, then close the chamber and charge it with a SMALL amount of your working gas at full pressure.  Seal up the pressure vessel and reheat to temps well above your standard operating temperature.  Stand well back!  If you don't test, you are driving towards a cliff with your eyes shut.  It's like static water testing but with the twist of temperature.

Amazing effort.  There are very few working stirlings out there and even fewer large ones, like yours.

[WXYZCIENCE]

BigBreaker,
Thanks again for your input. Research is the key to most innovation and most successful inventors steal their ideas from some where else and just add to them. At this point most of my methods are based on need. In building this engine one idea was to test different materials and configurations of the re-generator. this has been accomplished in the fact that I can remove the displacer / re-generator easily. I agree that the heat transfer characteristics of 306 stainless is on the low end. I have tested plain steel ,eg. S.O.S. they degraded and kept breaking up. I have purchased some brass scrubbers which I will test after next week. Sept. 10 -12 we have the unit entered in our local fair. Visual effect is what I am after here. Not to many people have ever seen one of these engine, let alone see one running.
 

[JW]

At this point most of my methods are based on need. In building this engine one idea was to test different materials and configurations of the re-generator. this has been accomplished in the fact that I can remove the displacer / re-generator easily.

I think this is really smart. In my mind its really not much different that some of the advanced DIY turbines featured. It just goes to show "simplistic designs" work...

When I first began to work with super-critical steam, I designed and fabricated a special heatexchanger. It is built on a pivoting hinge, and heatexchanger coils may be mechanically swept out of the fire-stream in the burner chamber "at any time".

I did face some critisim on the steam generator design, from the mainsteam or designers. However the unit was constructed in such a way, that I could safely generate 10,000 psi in the unit, and get a handle on how certian aspects of the system could be optimized from those specific observations. The system was/is beyond safety redundant, the trade-off was performance. In the end, low pressure systems are prefered, but until you actually "test the limits" you will never know. In some rare cases, performance gains are realized with low pressure, but you would never know to follow a certian design methodology, unless you've spent some time, just pushing the bounds of whats possible.

JW

[BigBreaker]

BigBreaker,
Thanks again for your input. Research is the key to most innovation and most successful inventors steal their ideas from some where else and just add to them. At this point most of my methods are based on need. In building this engine one idea was to test different materials and configurations of the re-generator. this has been accomplished in the fact that I can remove the displacer / re-generator easily. I agree that the heat transfer characteristics of 306 stainless is on the low end. I have tested plain steel ,eg. S.O.S. they degraded and kept breaking up. I have purchased some brass scrubbers which I will test after next week. Sept. 10 -12 we have the unit entered in our local fair. Visual effect is what I am after here. Not to many people have ever seen one of these engine, let alone see one running.
 

Here is an example of a copper scrubber:
http://www.amazon.com/Chore-Boy%C2%AE-Copper-Scrubbers-Pack/dp/B000RO5JC8

Check google and you can find the two copper scrubbers for $2-3.  Brass should work alright too, since it has a fair amount of copper in it, but copper is the best and probably the same price as brass.

I am not surprised that your regular steel scrubbers degraded at 500F.  Oxygen likes steel and it really likes steel at pressure and temperature.  You might want to put a hard vacuum before putting in the helium or using an O2 getter to scavenge it.  As you have learned, hot steel isn't bad as a getter!

On the regenerator, you can calculate the heat energy flux per cycle and then divide that by the specific heat of your regenerator (heat per degree * kg then times the kg of your scrubbers).  That will give you the average temperature cycle (well half of it) in the regenerator.  If you calculate 200F then I think you need more scrubbers b/c the regenerator does not have enough capacity.  IF its 5F you have plenty.

I came across a great paper on stirlings, their regenerators and working fluids a while back.  I wish I could find it because it had some simple formulas (like the above) to steer clear of big design mismatches.  I'll keep an eye out.  Good luck to you at the fair!

[willib]

Hey Joseph,That is a nice looking machine that you have there.

PS i too purchased some copper scrubbies , at least i thought they were copper, turns out they were copper coated steel , probably electroplated.

[spinningmagnets]

Good work XYZ, if anyone wanted to get some in-depth information about Stirlings, a great resource is the "Hot Air Eingine Society". Sadly you must join to be able to read the stored files, but doing that does keep the spam away.

I have transcribed the three major Rider patents into readable english. There were over 30,000 of them sold, and it is a mature design once you understand its subtle improvements over the previous. Electric motors and the diesel ended them. You can access the plain english patents in "Ron Roberts stuff" in the files section.

He did not have access to silicone lubricants, stainless steels, and Teflon. Since there was a small amount of working-air leakage, and air-pump and relief valve added make-up air at the point of lowest internal pressure. He ran double atmospheric pressure, as any more than that ignited organic-oil lubricants.

Since you are running helium to avoid oxidation, you could eliminate the displacer rod seal by moving the internal displacer slug with external magnets. The cylinder can be non-magnetic stainless-steel, and a ferrous steel band around the displacer-slug.

If you don't want to raise the pressure because of the bellows limits, consider making two more of these to stack one above the other. Rotate the orientation of the flywheels so a vertical crankshaft can be shared by all three. Having three also makes the engine self-starting. You only have to heat the bottom one, and the rising heat can be shrouded to also work the ones above. You won't triple the power, but an 80% increase in power without using more fuel might be worth the cost and effort.

Consider making the hot and cold ends of the displacer cylinders two separate pieces with a ceramic section in the centers to slow the heat creep from one end to the other. I would make the regenerator half that size. It would reduce the thermal mass (bad) but it would also reduce the volume of the working gas (good).

[WindriderNM]

For those interested is producing power from stirling engines there are 3 big dishes using stirling generators in the parking lot at the Belen NM. City Hall making power. There are posts elsewhere in this form about these.

[KraigM]

I've never seen Stirling engines that big. I've seen the really small ones that fit in the palm of one's hand and motors that are made with soda cans. I believe the soda can one's weren't Stirling engines but something similar. Do you have any video of your engine running?

[WXYZCIENCE]

KraigM , I have some video of the engine running. Problem I am on the slowest Line in the world. It would take me 4 hours to upload any video in any form. I have been moving around for the last year and have not been able to answer anyone. This is the first post I have been able to do for almost one year. I have been working on a new engine, and will probably be able to post it next Month. Thanks for the comment. Joe.