Stirling Engine Question

[Alyn Foundry]

Take a gander at this thread Paul.
https://www.modelenginemaker.com/index.php?topic=7561.0

You might like to style your engine on the lower HP engines that were all air cooled. In fact only the last three sizes as manufactured by L Gardner and sons were water cooled.

Regarding cylinder to platform joints I use Vaseline with a good flat mated surface. Alternatively acetic acid cure Silicone makes all my joints on all my models built to date.

   Graham.

[PaulR]

The Robinson just has a bolted connection between cylinder and the frame you could do that easy enough.

A couple of sections, the air moves along the central passage and up into the back of teh cylinder but you could take it to the bottom shown dotted in red.

From below you can see that the central air passage is surrounded by the water passages so not unlike passing the pipe through the tank but the drilled passages in the frame would be easier for you

Got it, thanks again. An alternative for cooling might be a bigger separate tank with simple connections to some drilled passages... thinkning.

[Alyn Foundry]

As a post script to Jason’s contributions here’s a version that H Robinson patented in the mid 1880’s.

More practical and cheaper to make than the elaborate double arm system but a tad more noisy.

<a href="https://www.youtube.com/watch?v=kJ30ubhD_Fg" target="_blank">http://www.youtube.com/watch?v=kJ30ubhD_Fg</a>


<a href="https://www.youtube.com/watch?v=_3qiYZRrE6g" target="_blank">http://www.youtube.com/watch?v=_3qiYZRrE6g</a>


   Graham.

[PaulR]

Thanks Graham, I was just ploughing through that thread. I got to the bit with the con rod roller which is not a mechanism I've seen before, I'll try to remember it, coudl come in handy!

[Jasonb]

Paul, you can always blow a little bit of air from your compressor through any cooling holes rather than water.

[Jasonb]

This might be an option, water tank at the crankshaft end and use it as a support for the crankshaft.

[PaulR]

Thanks, all good ideas. I was just reading up on the separate tank/thermosiphon idea but having holes in the bed plate like a Swiss cheese would might do for air cooling as per Graham's example. Also been rooting around for a suitable piece of plate but not finding anything that doesn't need a lot of work to get it squared up yet...

[Alyn Foundry]

Here’s another recently surfaced Gardner Number 5 hot air engine.

These engines weren’t built in vast quantities like the other smaller ones, consequently quite rare and highly desirable.

Photo courtesy of Mr O R Cater.

   Graham.

[PaulR]

I can't find anything thick enough for the bedplate so I'm thinking of something like this: an 1/8" plate with a thicker bar fastened below for attaching the displacer cylinder and carrying a drilled air passage. It would also give something more solid to fix the bush/rod guide above and the power cylinder support block to.

I could forget about water cooling and just put some holes or slots in the various components to increase surface area and help radiate heat away, eg the bedplate, the cylinder support block and even the bearing standard. Or maybe out some brass top hats in the bedplate to fill with water but that probably wouldn't make much difference. Thinking more...

[PaulR]

Taking the 3D mock-up a bit further I don't think my imitation of a Robinson engine will work unless I copy the more intricate links as well. My plan was a simple link between end of disp rod and crank pin and a single link with wrist pin from the piston but there will be too much lateral force on the former unless everything above the bed is moved up a lot higher. I don't fancy trying out a type of linkage I've never made before combined with a Stirling engine as it might prove trickier to fault-find if there's a problem. So, I think I'll look again at side-by-side cylinders but still arranged vertically. Baby steps...

Just remembered I hadn't taken into account relative sizes of piston/displacer which, in my original idea would have had the same travel (off the same pin). If I use the 1/2" tube for the displacer as per last time, make the piston 9mm and make the total travel just 8mm that gives a swept volume ratio of 1.91. With a throw of 4mm the sideways forces on the rod probably wouldn't be too bad.

[PaulR]

Drew up the relevant bits in 2D with the cylinder CL at top. The displacer (red) projects 1mm beyond its flange to locate it in the bored hole which has the air passage going off to left. A threaded bush (yellow) guides the rod through the bed plate(s). I've drawn it with 2mm clearance at the lowest point of its stroke. At right is mid-stroke. The side loading doesn't look like it would be too horrendous but opinions would be happily received!

[PaulR]

This might be an option, water tank at the crankshaft end and use it as a support for the crankshaft.

I see new member Spinner21's Robinson has similar set up although the tank is beside the cylinder and has some funky pipework to hook it up.

[Spinner21]

Hi Paul, as I said in my introduction, the Robinson type engine was based on an article in the Model Engineer from 1970 and isn't a perfect replica by any stretch of the imagination.
It was my first foray into Sterling engines I had no idea at the time what a Robinson engine should look like and just though it looked good, as there were no castings available I decided to make some patterns (also a first) and doubled the size.
I later read another ME article that said as made to the Westbury design the engine doesn't work but went on to describe some mods basically to make a larger displacer, I also reduced the power cylinder slightly to improve the swept volume ratio between the two cylinders. The original design did have a water jacket around the cold end which I did incorporate into my version so I just fashioned up a tank from sheet brass and the pipework was to get some circulation which also include a drain facility.
In the past it has run 5 to 6 hours non stop at several shows using only 1 small bottle of gas, although being almost all cast iron it takes about 15 to 20 minutes to warm up.
Andy.

[PaulR]

Thanks Andy, it's a cracking engine. What form does the displacer take, is it a closed 'drum' with or without regenerating material or is made from discs?

[Spinner21]

Hello Paul, if I remember correctly it is just a closed drum as at that time I had little or no knowledge of regenerators, the later made Ericsson was stuffed with wire wool and that one will run for a few minutes after turning off the heat.
Andy