Coffee Can Stirling (Remake of IronHorse's Caloric)

[joeby]

I had posted a while back in the plans section about a remake of IronHorse's caloric engine. I like Stirlings anyway; but I thought that his was exceptional, and obviously others did as well.

I decided to model the engine with a few changes that I thought may make a difference in how it runs. Sort of an experiment anyway.

Here's a photo of the parts I have gotten a start on.

The cylinder I finned because in one of IronHorse's posts, he mentioned getting a lot of heat on the cold end of the displacer cylinder. Just one of my attempts to reduce the heat.

I also decided to use a two-piece displacer cylinder joined by a threaded coupling, with the lid between the two halves.

I'm not sure this is going to work out, I might have a problem with leakage here. Anyway, the assembled parts so far look like this....

The individual parts are not at their final finish because I am fitting things together and making "edits" as I go. I know better than to start to make parts before the design is done; but sometimes I have an easier time deciding if I like the looks of something if I can actually pick it up and look at it, sooo....

Anyway, comments, good or bad, are welcome.

Kevin

 

[Davyboy]

Hi Kevin. Looks good so far. I like stirling engines just because I can't quite figure out how they run ???. I could watch them for hours. I sure hope to see more of this one.

DB

 

[joeby]

I haven't posted anything on this project for some time, it got pushed aside for a little while so I could get a few other things done. In between, though, I did manage to get a few hours to tinker. I am making an effort to build to the drawings I made to be sure they are correct, instead of my usual method of penciling in any corrections on the shop copies.

I'm still not quite sure of the crankshaft counterweights, they look a little on the heavy side, but I'll see how they work as is.

Ball bearings for the mains were rescued from a dead hard drive to try to reduce friction, but I had seriously considered bronze bushings. With two flywheels and a power cylinder bore of 1.02", I think they would have worked fine.

Kevin

 

[IronHorse]

It's looking great

I'm sure it will run!

 

[speakerme]

Looks great so far,

But like the blushing new bride, more! more!


Best Wishes

Chuck M

 

[chuck foster]

this build is looking real good............i could never fully understand how one of these engines worked.
i guess one day i will have to build one and see if i can figure it out.

thanks for the photos.

chuck

 

[joeby]

Here's another update on the Stirling.

Progressing slowly, there seem to be too many other things that need done, but I'm nearing the home stretch now I think.
The engine so far with the flywheel blanks.

I had thought the counterweights might be a bit too heavy, but that doesn't appear to be the case. I still have the displacer to make and I think it will add enough weight to balance things out rather well.

Two things that I feel may cause me problems later are the displacer con-rod angle and the power piston. The rod angle is rather steep and without a crosshead, it loads the gland more than I would like. No binding there at all, just more of a side load. Making the standards taller would have allowed a longer rod to help this area.

The power piston is causing me a bit of grief. The cylinder is brass and the piston is steel. The shop is kept at 550-600F, and the house about 750F. The piston was dragging in the bore, so I polished it with 400 grit emery paper until it was free enough to move easily, but not drop through under it's own weight. After being in the house all night, it has become rather free. Hopefully it's not too loose now. I may add several vee grooves to try to minimize any air leakage. I have built an LTD Stirling that has an aluminum cylinder and graphite piston that has the same problem, although exaggerated because of the lower working pressure, I think. It is very fussy about being left alone until it gets to room temperature or higher, at lower temps, it seizes up.

Just a displacer, hot-cap, and flywheel spokes to go; then it's time for a test run.

Kevin

 

[Metal Butcher]

I'm new here and self taught rookie.

However I did build one Stirling engine called "Moriya".

I used brass for cylinder and I "think" CRS for the piston.
Had problems to. It would sorta run, Then it would not run, Sorta drove me crazy!
Now that I think about it, seems it would sorta run in the basement. Does this make any sence?
It took a while plus a guess that the power cyl/piston was the culprit!
Long story short, I made the cylinder out of a bronze bushing and the piston from purchased quality cast iron.
Problem solved! It now runs great first time every time, and other than replenishing the fuel it runs for hours until I get bored with the refueling.
Its a fan desighed by Dr. Robert Senfit.

-MB

 

[joeby]

MB,

I think I may just remake the piston out of cast iron. I'm afraid that loosening the fit enough to allow it to work freely at varying temperatures is going to allow too much leakage. I don't believe that a graphite piston is the answer either, still have to deal with the expansion/contraction of the power cylinder.

Anyway, I managed to disappear into the shop for another two hours this evening and finished machining the flywheels.

I want to try to make enough time this week to finish the displacer and hot cap so I can see if/how it runs.

Kevin

 

[Metal Butcher]

Sorry, I got engrossed and forgot to say your engine looks stunning and the workmanship is superb!

Also, I made a mistake (old age memory loss) The designer was Dr. James R. Senft.

The engine (fan) I built was from plans published in Steam and Sterling engines you can build, published by Wildwood publications. Division of Live Steam, a very good "idea" book for those wishing to build "hot air engines".

A study of materials suggested by published builders might help those experimenting with new designs.

Edit: Check out " thermal expansion of metals" using a Google search.

-MB

 

[joeby]

MB,

Thank you! I'm just trying to keep up! :bow:

I have a half-sized Moriya fan that I built some years ago, it runs fine; but thinking about it now, it may very well have a cast iron piston in it.

At any rate, I am well aware of the expansion rates of different materials; but unfortunately I didn't put enough thought into this application. I was more concerned possibly with appearance than the problem of a leakage issue at start-up temperatures. Leakage at higher temperatures will be greater as the cylinder will expand ahead of the piston; but I had hoped the higher pressure differential would help overcome that.

I have some other designs that I'm looking at also that use several different materials to try to make the best use of heat transfer and expansion.

Amazing how much time I can spend re-inventing wheels!

Kevin

 

[joeby]

Brought the engine inside to sit for a few hours yesterday while I finished up the hot-cap for it. As I mentioned earlier, it loosens up a bit after everything warms up slightly.

I finished the hot-cap, ended up making it from a piece of H-13 steel because I didn't have any stainless big enough. Anyway, I finished putting it together and tried running it on my alcohol burner.

It gave a good effort, but wouldn't run on it's own more than a few seconds. I noticed a "bump" when the displacer was near the limits of travel, so I pulled this displacer back out to sort through it. The clearance between the displacer and cylinder was close, but maybe too close. I was thinking the "bump" was from compression in the displacer cylinder. A quick setup in the lathe, and I had another .035" off the diameter.

Re-installed the displacer this morning and tried again. After a little time to get some heat in it, and a little tweaking on the displacer "timing" we now have a runner!

The next thing on the list is to make a base for it and clean up a few rough edges. I haven't decided on material for the base yet, but it will probably be wood. With the engine sitting on top of a coffee can, it is rather noisy for a Stirling. I'm hoping wood will dampen the sound a little.

When I get the details finished up, I will see if I can figure out how to get a video of it.

Last but not least, thanks IronHorse for the inspiration!

Kevin

 

[IronHorse]

Nice work om the engine, can't wait too see the video!

I had the same problem with the piston, I just had to lap it a couple of times. I am sure yours will run for longer time than mine. I have to limit running to 5 min. max. for fear it will melt down!



IronHorse