My engines

Discussion on Stirling or "hot air" engines (all types)
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Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

My engines

Post by Robert Hornby » Sun May 25, 2014 8:47 pm

I have built these engines a couple of years ago but not managed to get them to run.
The Cup Of tea engine has a graphite power piston and is a ‘neat’ fit into the bronze cylinder. It requires the lightest push to move it down the cylinder.
Image
I have balanced the flywheel/crank assy with all parts connected as best as I could. I have placed the displacer over a light globe (for greater heat) but without luck.
Any ideas on this one?

The second engine has a flame from a wick (not shown in the photo) and it spins from a finger quite easily. Still a no go.
Image

Robert

Ian S C
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Location: New Zealand

Re: My engines

Post by Ian S C » Tue May 27, 2014 1:34 am

Hi Robert, nicely machined engines. I can't see both cranks on the LTD motor, are they set at 90*, ie., if one is at 12 o'clock, the the other should be at either 3 or 9 o'clock (that's a lot of use if you have a digital watch :laugh: ). You might have to use some Blue Tac or something on the flywheel as a counter balance, maybe in one of the holes in the web. Perhaps you don't drink hot enough coffee!
They look to good not to work, might be too accurate/clearances to close, friction is about the biggest killer of hot air engines, and this can be down to the materials chosen for the likes of power piston, and cylinder. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Tue May 27, 2014 3:26 am

Thanks for that Ian, yes the cranks are at 90 deg. and I have tried the blue tac for balancing. I know that the two important things for a hot air motor to run are - minimum friction and minimum air leaks. Obviously these two requirements are in opposition to each other so which would be the most important?
Robert

Ian S C
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Location: New Zealand

Re: My engines

Post by Ian S C » Wed May 28, 2014 6:01 am

Robert, I was thinking about your LTD motor today, and wonder if your flywheel is too heavy, the FW on my LTD, a bigger motor, displacer 150 mm diameter, the FW is 220 mm dia., The rim is a ring of aluminium9 mm deep x 6 mm wide, the spokes that hold it to the hub are 6 bits of bike spoke.
The top and bottom were made from 2 fry pans, the rim for the FW was cut from the bigger of the two. Motors the size of yours get by with using old CDs. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Wed May 28, 2014 3:06 pm

Good point Ian, I will remove some weight from the flywheel and try again. It will have to wait a little while though as I am knee deep in boiler making at the moment.
thanks for your interest Ian.
Robert

Ian S C
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Re: My engines

Post by Ian S C » Fri May 30, 2014 5:46 am

Robert, nice boiler, a steam engine is fairly likely to run first off, no matter how badly built, but a Stirling Engine is a bit of a problem if it won't go, it would not be the first time I'v had to take a day away from the workshop with a sore wrist from trying to start some of my earlier motors. Ian S C

loccd
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My engines

Post by loccd » Thu Jun 05, 2014 5:21 pm

At the first engine, it is look quite heavy for a low temp engine. Is it right Ian SC?



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Ian S C
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Location: New Zealand

Re: My engines

Post by Ian S C » Fri Jun 06, 2014 3:33 am

Loccd, yes I think so.
Robert, you may need to polish the piston a little. Spin it in the lathe, and use a strip of paper just as you would use wet and dry paper on a cast iron piston. Think pencil paper, graphite paper. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Fri Jun 06, 2014 10:55 pm

Thanks guys, when I look at the flywheel it does seem a bit on the heavy side (although it is per the original plans I followed) so I will be lightening it up quite a bit, but as I mentioned earlier I am focusing on a stem boiler at the moment.
Robert

Ian S C
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Re: My engines

Post by Ian S C » Sat Jun 07, 2014 4:18 am

Robert, is it one of Jan Ridders' motors? Jan is a member of the forum.
I presume (shouldn't) you have a good seal on the displacer cylinder, between the plastic cylinder, and the top and bottom plates. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Tue Jun 10, 2014 12:46 am

Ian,
I will have to dig out the drawings for the engine (it is about 4 years ago that I built it) to see if it is one of Jan's designs. The seals on the displacement cylinder are good as far as I can tell, I have 'O' rings between the cylinder and the covers. That has raised an other question about what the clearance should be between the displacer and the cylinder, I have tried several different displacers of varying diameters but to no avail. The cylinder is 94.25mm inside dia. The wall thickness is 11mm. I have tried displacers between 88.2mm dia. and 92.6mm dia. Until I find the original drawings I cannot remember what the original dia. should have been. The displacer is made from engineering foam styrein (sic) with a wood plug in the centre to hold the rod.

Image

Robert

Ian S C
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Location: New Zealand

Re: My engines

Post by Ian S C » Tue Jun 10, 2014 3:40 am

Robert, I think my one has some where about 3mm to 6 mm clearance at the side on a 150 mm diameter, can't remember the clearances top and bottom, I just sort of made it up as I went, tried a number of power cylinders, from 10 mm to 25 mm, and settled on the 25 mm one. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Wed Jun 11, 2014 12:19 am

Thanks for that info Ian, I have commenced work on lightening the flywheel by about 50% because of what happened last night.
I belong to a local club that has its main interest centred around old farm hit and miss motors and the like. A couple of members build models and some others passions for old outboard motors or lawn mowers. Anyway last night was our monthly meeting to discuss happenings and what each of has been up to since the last meeting, and our president brought along a ‘show and tell’ - non other than a model Stirling engine circa very early 1900’s. he poured a little Metho in the cup around the displacer (which was at the top) waited 3 or 4 mins to get things hot and with a couple of flicks on the flywheel she spun like a beauty. Had I had my camera with me I would have taken a photo but alas I didn’t.
So naturally I was a bit miffed that such a 100 year old model and not looking like there was too much in the way of quality or fine engineering/machining when mine wont run.
So as the steam boiler has reached a mile stone in that I have just successfully pressure tested it I feel I can put it to the side for a while and get enthused again with hot air engines.
I will use one of my displacers which give around 3mm gap to the cylinder wall.
Robert

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: My engines

Post by Ian S C » Wed Jun 11, 2014 4:32 am

Robert, I don't suppose you got the makers name of the old hot air engine, my guess would be a German toy maker, Carette is one, Lehmann is another. Ian S C

Robert Hornby
Posts: 8
Joined: Sun May 25, 2014 3:35 pm
Location: Failford, Mid North Coast NSW Australia

Re: My engines

Post by Robert Hornby » Thu Jun 19, 2014 3:16 am

Ian, there was no makers name on the engine, next time I see the guy I will try to get a photo of it. In the mean time I have taken your suggestion of the flywheel being too heavy and done a bit of a job on it. I seem to have a problem adding a video to this blog, I succeeded on MEM forum so it can be seen there.
Robert

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