Head cold from Hell and maybe a Stirling engine

[Brian Rupnow]

I didn't do a whole lot today, spent half of it running errands around town and going to the toolshop to buy 1/8" endmills. I did manage to finish a piston. I departed from the Moriya fan drawings because they had the piston and the piston pivot made from two separate pieces bolted together. I couldn't see any benefit to this, so I made the piston a one piece unit with 4 "lightening" holes. I turned the piston to .002" oversize, then finished it up with 280 grit emery cloth strips, and once I got it down far enough to start into the bore of the cylinder I lapped it in with #600 grit carborundum paste.

 

[Brian Rupnow]

Time for an update. This morning I completed the connecting rods for both the power piston and for the displacer piston. All I really have left to do now is to make the displacer piston and guide bushing for it and cut out/install the phenolic insulator between the hot end and the frame plate. In the video you will notice that I suffered a fit of tangle-mouth and said that all I had to do now was make the displacer cylinder. I meant to say "displacer piston".

[ame]https://www.youtube.com/watch?v=tCqg6uvvc2U&feature=youtu.be[/ame]

 

[Brian Rupnow]

This was the morning to make gaskets and machine the phenolic insulator that goes between the hot cylinder and the machine frame. It machines very well, but its stinky dusty damned stuff. I wore a simple particulate mask and had the window open (brrr) while I machined it. Seems to have turned out well.

 

[Brian Rupnow]

 

[Brian Rupnow]

This morning I picked up the thin wall stainless steel tubing for the displacer piston, and machined the two ends from aluminum. Next step will be final assembly of the displacer and then assembly with the rest of the engine.

 

[Brian Rupnow]

Everything is back together, and I have tried the first run. No joy yet. The engine wants to run, but there is a bit too much friction where the displacer piston rod passes thru it's guide bushing. The displacer piston is not rubbing on the inside of the cylinder. With the crankshaft throw disconnected from the piston rod, it is difficult to push in and out with my fingers. Everything is too hot to mess with right now. I have to think on this a bit---In the Moriya fan where the cylinder sets vertically, the weight of the displacer piston would not be putting any side pressure on the guide bushing, but I don't think that is whats happening here. If that were the case, my engine should run freely if I stand it on end. I may have to take the hot side of the engine apart and work some magic on the rod to bushing fit with some 600 grit compound.

 

[Brian Rupnow]

Disassembly shows that yes, the piston rod is definitely binding in the bushing. I can remedy that with some 600 grit compound. More damning though, is that the pressed in piston cap opposite the rod is lose, and those things have to be air tight. I had pressed it and Loctited it, but the heat burned away the Loctite and the press fit was too light. I will think on this a bit and see if I can expand the existing cap mechanically or make a new one which would be a tighter fit.

 

[Brian Rupnow]

This shows me pressure rolling the end of the displacer cylinder to decrease the inside diameter a bit to get a stronger lock on the cap which had came loose previously.

 

[Brian Rupnow]

And there we have it my friends---FIRST RUN!!! I still have some tuning to do and some proper pivot pins to make, but Lord, Lord, I got a runner.
[ame]https://www.youtube.com/watch?v=q380skpC-AA&feature=youtu.be[/ame]

 

[ZebDog]

I have been watching this build congrats on your first running stirling

 

[Sleddog]

Way to go Brian. Congratulations on the runner.

 

[Brian Rupnow]

Way to go Brian. Congratulations on the runner.

Thanks Sleddog--I've spent the rest of the afternoon trying to refine things a bit. There are an absolutely amazing number of places that an engine like this can "bind".

 

[Brian Rupnow]

And a second run after I have spent the afternoon taking out any "binds" I could find in the engine. It's just as I thought when I started--these engines don't have enough power to get out of their own way. The biggest challenge seems to be keeping them running once they have found their "sweet spot".
[ame]https://www.youtube.com/watch?v=g9a5bSxOGaQ&feature=youtu.be[/ame]

 

[fcheslop]

Congratulations on a runner
Be careful these engines can become as addictive as they are frustrating
kind regards
frazer

 

[ShopShoe]

Congratulations Brian.

It's great to get a runner that quickly. Your time from conception through design to build and run have lessened considerably since I started following your various projects.

I have had a stirling on my future build list for quite a while and you inspire me not to give up on that.

--ShopShoe

 

[Brian Rupnow]

Okay--Perhaps a mini personal milestone has been reached. I have built a Stirling engine. It runs. It runs great, but it doesn't run long before the cold end heats up and with the loss of heat differential between the hot and cold engines it slows down and quits. I am not terribly impressed!! (Maybe a little bit impressed). I have no really good way to make the hot end any hotter, but I can make the cold end stay colder!!! If I make a new cold end cylinder with no fins and put a water jacket around it, using the same type of seal that I used on the Rockerblock water reservoir, then circulate cooling water through the jacket, the cold end should stay cold.

 

[Brian Rupnow]

Just for the heck of it, I set the engine up this morning with the cylinders vertically aligned as they were in the Moriya fan, which I copied. The engine started up and ran like a trooper. Then after it had ran for about 4 minutes, the cold end heated up and it gradually slowed down and quit, as the hot and cold end temperatures equalized. to me, this only confirms the need for some type of cooling system on the cold cylinder.
[ame]https://www.youtube.com/watch?v=WAN8n9cw0YA&feature=youtu.be[/ame]

 

[fcheslop]

Hi Brian, A stainless steel hot cap with a heat dam machined into it would help
Also that seems a mighty big flame you are using this wont help . The flame should have a sweet spot near the very end if its further up I would check how much clearance you got between the displacor and the end of the hot cap.Also check the power cylinders gap as dead space and air leaks kill these engines as does any binding how ever small
Moriya runs for a good hour or so on the original meths burner
The insulating plate Im not sure how good that stuff is I used some of that insulating glass plate they use on oil heated injection moulding tools it goes between the tool and the platen sandanyo plate Iv known it as
Never the less youve a runner congratulations and happy fiddling with it.
kind regards

 

[Brian Rupnow]

I could hear a noise when turning the engine over by hand, the noise occurring when the displacer piston was at its end of stroke farthest from the crankshaft. I just pulled the displacer cylinder apart, and sure enough, the piston cap was loose again. Time for a little experiment to see if I can silver solder the stainless I have. If so I will make a new end cap from thin mild steel and silver solder it on.

 

[Brian Rupnow]

I've taken this as far as I can without adding auxiliary cooling to the cold end. I made a new piston cap out of mild steel and it easily soldered to the stainless steel piston tube. The engine starts fine. It runs for about 3 minutes, then gradually slows down and stops. At the end of that 3 minutes the cold end of the displacer cylinder is to hot to lay your finger against. I wonder a bit about the weight of the flywheel being too great, but again, going by the Tubal Cain videos, he casts his flywheels from lead, so my creation of aluminum center with bronze outer rim should be ballpark close. I'm very happy that my engine runs, and that it ran so easily without a ton of messing around with it. I would like it to set and run like that for two hours. If I am bored next week, I may make a water cooled version just to see what happens.