Stirling engine won't run

Discussion on Stirling or "hot air" engines (all types)
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Rahmsauce
Posts: 4
Joined: Sat Mar 02, 2019 3:27 pm

Stirling engine won't run

Post by Rahmsauce » Sat Mar 02, 2019 4:07 pm

Hello,
I need some help getting my first stirling engine to run. The displacer is made out of cotton cosmetic pads. As it is quite heavy (about 10g), I added a counterweight (magnets) onto the flywheel. I have also checked for air leaks and couldn't find any major ones. When I disconnect the displacer and power piston, and spin the flywheel, it stops after about 9 seconds. In addition, I added ice on top of the engine to increase the temperature difference. Furthermore, I tried the following troubleshpoting tips: http://www.stirlingbuilder.com/troubleshooting-tips but none of them seem to get the engine running. However, I feel like the engine is easier to spin up by hand, when it is heated from the bottom and cooled from the top. Maybe the included images can help solve the problem.
Attachments
IMG_20190227_135739-1107x1255.jpg
Measurements in centimeters
IMG_20190227_135739-1107x1255.jpg (168.8 KiB) Viewed 121 times
IMG_20190302_232518-1149x1634.jpg
IMG_20190302_232518-1149x1634.jpg (482.62 KiB) Viewed 121 times

Ian S C
Posts: 2184
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Stirling engine won't run

Post by Ian S C » Sun Mar 03, 2019 1:49 am

First thing I see is the main bearings, or lack of. The crankshaft appears to be just using the ?wood as the bearing, and one of the most important things with Stirling Engines is reducing friction to the absolute minimum. One way to do it would be to get some tin (from a tin can, get a bit of steel like a nail the same diameter as the crank shaft and knock it through the tin, make sure that the crankshaft fits the hole freely. Open out the hole in the wood and fit the new bearing over the hole. Don't drill the hole, this would make the surface too small and it would soon start to wear the shaft.
Next, find a suitable sized tin can to make the displacer from The top needs to be sealed, solder would be good, but epoxy glue could stick a lid on the can. Drill, or poke a hole in the centre of the top and bottom of the displacer, and pass the displacer wire through, bend it over at right angles at the bottom, seal both holes with solder.
You might need a heavier fly wheel, you just need to glue some weights around the disc near the rim, don't over do it.
See how you get on, I don't normally make tin can motors although I have done, and I respect anyone who builds one and gets it going. If you look at the top of the index page you will find plans for a tin can motor by Boydhouse the forum host.

Ian S C

Rahmsauce
Posts: 4
Joined: Sat Mar 02, 2019 3:27 pm

Re: Stirling engine won't run

Post by Rahmsauce » Sun Mar 03, 2019 11:18 am

Thank you for your quick and very detailed reply, Ian! I've tried making the top of the displacer more air tight as you said. However, I'd like as many parts of the engine to be removable in case I need to change something. So instead of using solder, I tried reducing the air leak by sticking fingers of rubber gloves at the contact point where the displacer and the displacer top meet and applying some pressure onto the cylinder top (I know this sounds quite like a ghetto solution but it at least "feels" more air tight).
Then, I did some testing: I disconnected the crankshaft and heated the engine from the bottom and cooled it from the top. I waited a few seconds and noticed a quite substantial temperature differential when I touched the walls of the displacer cylinder at the top and the bottom. So far so good. However, when I move the displacer up and down manually (by hand), the diaphragm of the power piston doesn't move at all. Does that mean there is still too much air leaking?
IMG_20190303_183402-1728x2304.jpg
Rubber glove fingers at the top of the displacer cylinder
IMG_20190303_183402-1728x2304.jpg (674.58 KiB) Viewed 103 times

Johnwick88
Posts: 2
Joined: Wed Mar 20, 2019 8:01 pm

Re: Stirling engine won't run

Post by Johnwick88 » Wed Mar 20, 2019 9:59 pm

Insufficient pressure, large cylinders

Ian S C
Posts: 2184
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Stirling engine won't run

Post by Ian S C » Thu Mar 21, 2019 1:57 am

I suspect that it may be to do with the diaphragm, I'v not had much to do with these, I recommend that you go to the top of the index page of this forum, and read through the thread on making a simple Stirling Engine, this has a bit in there that tells you how to make an epoxy piston that could replace the diaphragm.
Ian S C

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