Head cold from Hell and maybe a Stirling engine

[Brian Rupnow]

I'm sick.--Sicker than a friggin' dog, suffering from a head cold!! Small wonder though--All my kids have had it, my grandkids have had it, my wifes had it, and the guys at work have had it. I thought I was going to be lucky and have it pass me by, but no such luck. My head feels like a giant bucket of snot!! Now that I have shared that disgusting fact with you----I'm thinking of maybe building a Stirling cycle engine. I've always stayed away from Stirling engines, because they barely have enough power to get out of their own way. Today I watched a couple of YouTube videos by Tubal Cain, where he does a reasonably good job of explaining the operating principle of these engines. I would prefer to build a simple all metal engine with a power piston and a displacer piston, similar to the one in tubal Cain's video. I'm not really after the polished brass and glass test tube variety, which are works of art.--Nor am I after the "two tin cans and a piece of wire" variety. The one in Tubals video looks about right to me---Plain Jane, but all metal. I will have to see where I can get plans of that.---Brian
https://www.youtube.com/watch?time_continue=1&v=DkfXd8634WY

 

[Brian Rupnow]

I just spent a good portion of my afternoon watching all four videos of Tubal Cain building a Stirling engine from scratch. He makes it look easy, but he is quite emphatic about warning that there are no plans, no dimensions, and no blueprints available. All I was able to glean dimension wise, was that the bore of both power piston and diffuser piston was about 3/4", the crankshaft and diffuser piston rods were 3/16" diameter, and the connecting rods were 1/16" x 1/4" brass bar, the piston pin was either 1/16" or 1/8" diameter, and the flywheel was 3 1/4" o.d. the stroke on the diffuser side looked to be about 1/4" greater than the stroke of the power piston. The stroke of the power piston looked to be about 1 1/4". the diffuser piston was a loose fit into the diffuser cylinder to let hot air to bypass the piston and the power piston had to be a very very good fit into the power cylinder. Although his engines used castings for the two main components, I see no reason why they couldn't be whittled from aluminum barstock.
https://www.youtube.com/watch?time_continue=1&v=DkfXd8634WY

 

[Brian Rupnow]

The displacer piston has about 1/16" radial clearance from the cylinder walls and the displacer cylinder is connected to the power cylinder by a 1/4" diameter passage. It seems only logical to me that the power piston at top dead center must not travel past this 1/4" passage.

 

[Brian Rupnow]

After carefully watching and listening to all of the associated videos, I have learned that the displacer cylinder may in fact be 7/8" diameter. Apparently its not critical, as long as it is about 1/8" larger than the displacer piston. The displacer piston is actually the outer aluminum shell of an industrial paint or ink marker with the felt removed from the inside and a custom aluminum "bung" Loctited into the open end. At top dead center and at bottom dead center, the displacer piston should be about 1/16" clear of the inside ends of the cylinder. The power piston is machined from mild steel. The angular offset between the crankshaft throw on the power piston and the displacer piston is 90 degrees. It seems that "displacer" and "diffusor" are basically the same thing.

 

[fcheslop]

This may give you some more info
i normally build with 1mm clearance for the displacer and use a ratio of 1.6:1 upto 2:1
http://ridders.nu/Webpaginas/pagina_ervaringen_tips_stirlings/ervaringenstirlings_frameset.htm
I reworked Rudys tractors engine and she has a little bit more power
Mainly reducing dead space

 

[Tom Jamboretz]

Perhaps this link would have plans that may be of help. Also IC engine plans.http://www.jerry-howell.com/Duplex.html TJ

 

[Hopper]

Be careful. Stirling engines can be very addictive! And quite hard to get running sometimes.
Here's a link to detailed plans for Dr Senfts "Moriya", a well proven working model. It's a table fan but the basic design can easily be laid down flat with a flywheel to make a more conventional engine.
Link: http://courses.washington.edu/me355b/Fan_Project_Description.pdf

A common mod is to make the displacer cylinder ("hot end") from stainless steel so the heat does not conduct well up to the "cool end", as it is the temperature differential between these two ends that makes the whole shebang work.

Have fun! (and hope you get well soon)

 

[Journeyman]

Brian, I can recommend the various books by James G. Rizzo about Stirling and other hot air engines. plenty of plans and info on sizes etc. I think his first book was "Modelling Stirling and Hot Air Engines" published in 1985 so may be a bit hard to find copies now. Made my first engine from one of his designs, some details of my effort *** HERE *** all made from scrap, there is a PDF plan on the website.

John

 

[Brian Rupnow]

I dosed myself up with antihistamines and managed to stagger in to my office across town today, and at the end of the day watched all four of Tubal Cain's Stirling engine videos again. No offence to Tubal Cain, but the work in those videos seemed--Ahem---Pretty damned crude. At least "crude" in comparison to a lot of the work I've done on my own engines. However, the engines ran.--and they ran pretty darned good. It's a shame that a few more reference dimensions weren't given, but with what information was given it seems like it won't be difficult to extrapolate all of the unknowns. Of course if I try and build my own version of what Tubal has done, I won't be casting the parts. They will be cut from bar stock. The only thing I won't have absolute control over is the displacer piston, as it has to be made from a purchased aluminum bodied ink marker. Even if I don't make this engine, it will be a nice little design exercise. I probably will make it, if only because I have never made a Stirling before, it doesn't have a lot of complex parts, and it seems to be a fairly "forgiving" design.

 

[fcheslop]

They are forgiving sometimes The main reason for failure is friction and air leaks
Homeware sections in shops can provide good materials for the hot caps and displacors
You can tell the Stirling builders they are the ones with a vernier measuring ladle handles
Another good source if you can find an electrical contractor using stainless conduit and the bigger engines stainless exhaust pipe although Im sure you already know that
cheers

 

[Sleddog]

It's a shame that a few more reference dimensions weren't given.

Drop him a PM asking for them.

 

[Brian Rupnow]

Drop him a PM asking for them.

No, he mentions 2 or 3 times throughout the videos that he "has no plans" and that he doesn't "sell blueprints" and that he "makes it up as he goes along". I get the idea that he doesn't want to give out that information and I can respect that. His instructional videos on both the build and the theory behind the working principles are very well done. He does however, at the end of the final video give blanket blessing to anyone who wants to "copy his work".

 

[Brian Rupnow]

Tubal mentioned that his flywheel was made from lead and was 3 1/4" diameter with a 3/16" center-hole. One of his engines had a spoked flywheel and one on a similar Stirling had the more simplified flywheel I have shown. No width is mentioned, but best guess is about 5/8" overall thickness. My flywheel will be 3 1/4" diameter x 5/8" wide made from cheap old mild steel.

 

[Brian Rupnow]

Tubal had the advantage of casting his crankshaft supports as part of the main base. I don't have that option, as I am building from barstock, so my bearing stands will be 3/8" thick aluminum (maybe brass for some bling) bolted in place with #10 shcs from under the base. I will also counterbore my bearing stands for two 3/16" ball bearings. These ball bearings will have the seals removed and all traces of factory grease washed out with laquer thinners to give the absolute minimum of rolling friction. That 1" wide x 3/16" slot in the other end of the base is going to be for an alignment key for components which will be built up from the base..

 

[Brian Rupnow]

And---Oh My!!!--What if we were to use the top end with the diffuser and power cylinder and mounting plate from the Moriya fan which is proven to work well---. The finned "cold end" will dissipate heat better than the solid casting used by Tubal Cain, and gets around the issue of me not being able to cast the displacer cylinder into the body like he did.--Also sets up the possibility of a cooling fan.---The power piston is the same diameter on both the Tubal Cain engine and the Moriya fan, but the Moriya displacer piston is slightly larger in diameter than the tubal Cain engine. (0.91" as opposed to about .780" dia.)

 

[Brian Rupnow]

My cold is getting better. It's still there, but its going. I will try my favourite medicine soon---Gargle with whiskey for three minutes, then swallow. Repeat as necessary. I have worked most of today on this design, and although it is slowly taking on a bit more machining content than I initially wanted, I like the design. This is a very nice "middle of the road" example of an engine. It is not all polished brass and varnished base, but it's a step up from what I initially had in mind. I'm in no rush to start machining, so will keep working away at this 3D model until I have everything as I want it.

 

[Brian Rupnow]

Makes a nice size package!!

 

[Brian Rupnow]

So there we have it---Pretty as a new pup!!! I can't say I'm really enthusiastic about the studs called for in the Moriya fan drawings, but I will probably change them up to socket head capscrews when I actually get to building it. The entire top end including both diffuser and power cylinders and pistons are taken directly from the Moriya fan drawings, and if you take a look on YouTube there are literally dozens of videos showing Moriya fans a operating. The offset on both power piston crank-throw and diffuser piston crank throw match that of Moriya's. The distance from the bottom of the cylinders to the centerline of the crankshaft again matches the Moriya fan. The main base, flywheel, and crankshaft are more along the lines of what Tubal Cain shows in his videos. The only "exotic" material on the entire engine is that brownish colored piece of insulation between the hot end of the diffuser cylinder and the 1/2' plate it bolts to--It is called up as being asbestos, but I will try and source an insulating material that is a bit more health conscious.

 

[Brian Rupnow]

The good news is that after scrounging around in my "left over pieces" bin, I've found enough material to build everything for this model. The bad news is that my printer just ran out of ink.

 

[Brian Rupnow]

I wouldn't want you guys to think my life is dull or boring in any way---But it is winter. I had nothing to do today, so I started making parts. Todays work yielded the engine base. The eagle eyed among you may notice that the base looks a bit thicker than it does in the solid model. It is. I had a piece of 2" x 1" material, and decided not to spend any time making it 3/4" thick. This will ultimately work to my advantage because it gives a little more room to slide a can of Sterno under the hot end of the displacer cylinder. Today is my 29th wedding anniversary so me and good wife are off to a fancy restaurant for dinner.