Stirling Hot Air Engine

[Mr Bowcat]

Morning all.

Another model engine, this time an external combustion heat engine. Quite interesting as to the way it works by using the heating and cooling of air in an sealed environment to create oscillation.




If anyone would like to look at the plans in more detail they are freely downloadable from https://journeymans-workshop.uk/imag...r/gammahae.pdf

The stock for this project was around £50, so fairly comparable to a decent plastic kit.

[PaulTRose]

This looks very intetesting

[Jim R]

Definitely interesting. Is the material you have copper, aluminium or what? Sounds reasonably priced.

[papa 695]

Very interesting Bob, is it a working model? I’ve just took a seat at the front for this.

[Mr Bowcat]

Jim, a mix of cast iron, steel, aluminium and brass. I realised when placing the order that a lot of it had a minimum spend, so by playing with the lengths I was able to get far more than I will need for the same price. Always good to have extra in case I screw a part up.

Ian, yes it should work when it's completed, assuming I build it correctly.

[minitnkr]

......verrrry interesting......

[Mr Bowcat]

Morning all.

With Storm Darragh raging all weekend I decided the safest place to be was the workshop.

I've been studying the plans and chose to tackle the displacer cylinder first, mainly because it involved silver soldering which I have never done before.

It started with some 16.5mm OD seamless steel tube which was turned at each end to square up and to get the correct length. This then had a piece of 1mm steel plate silver soldered to one end.




After turning off the excess material on the lathe I then made the flange for the other end. A piece of 2.5mm steel plate was squared up and drilled for the holes for mounting to the block later on. I also dropped in a center hole. The piece was then mounted in the lathe and the centre hole employed to get in concentric. Once done the hole was drilled to 14 mm, then a boring bar was used to open up the hole to just over 16.5mm. It needed to be slightly larger than the tube to allow somewhere for the solder to flow.To ensure it was the right size I bought a set of snap gauges (OK, it was just a good excuse to buy some). This was then soldered on and after some clean up the part was complete. You can see in the last pic the lighter coloured ring, which is where the solder went.










I was really pleased with the silver soldering, it's not the prettiest, but as a first attempt went well, and more importantly the joints are strong and air tight.

With the cylinder out of the way I went on to make the displacer. This is a relativity simple part, just a length of 13.5mm OD ali tube. Each end was rebated and a plug of aluminium pressed in and turned down flush. Because this part will be at the hot side of the engine the plugs couldn't be chemically fixed with glue/threadlock, so they had to be made to an interference fit (a couple of thousandths of a mm larger than the inner diameter of the tube) and pressed in with my vice. The longer plug has a hole drilled in and tapped for M4.



Next up was the displacer rod, a length of 5mm drill rod, threaded one end M4 to screw into the displacer, and a 1.2mm hole and 2mm slot in the other end to eventually connect to the crank via a yoke. Another fairly simple part, though did involve using the murder saw (slitting saw) which frankly terrifies me every time I use it.




Last part to be made was a pin for connecting the displacer rod to it's yoke. I actually made two in the same set up as another will be needed later down the line. These were tricky as they are only 1.2mm diameter, and were turned down from a 3mm stainless steel pin.




And that's the displacer assemblies complete. The tube is the part that is heated externally, causing the displacer to be pushed by the expanding hot air. However this is not a piston, the displacer itself is slightly smaller than the internal bore of the tube, which allows the hot air to pass by it and on through the block to the cold side of the engine. You can see the gap in the last pic.

[Steven000]

Great machining Bob, looks all very nice and shiny!

[Jack L]

I don't really understand anything that's just happened, but it looks i impressive already!!

[Airborne01]

Like Jack says - don't understand a tech word but am intrigued, impressed and intimidated by your skill set!
Steve

[Miko]

I envy your workshop and tools!!!

I have a Stirling engine powered by a cup of tea!

Miko (I wish I had a mini lathe!)

[Jim R]

As others have said the technicalities are beyond me but it's very interesting. It all looks very neatly and skillfully done. Sounds as if you're having fun and developing new skills.

[Mr Bowcat]

Many thanks chaps.

If anyone would like me to clarify any of the terms or techniques, feel free to ask.

[minitnkr]

I'm experiencing much tool envy. Great work. Murder saw very aptly named. Scary looking!

[Mr Bowcat]

Cheers Paul.

Yes, the saw not only looks scary but has a tendency to shatter if pushed too hard. The thought of High Speed Steel shrapnel flying past your head isn't pleasant.

[HAWKERHUNTER]

I have no words Bob. I think I need to stop following your builds as they make me feel like an absolute novice. Great works mate.

[Mr Bowcat]

Cheers Steve.