My 18cc Alpha Stirling Engine

[PlaniTechic]

Hi
In this thread i would like to show my little 18cc Alpha Engine.

Alpha Cut.JPG (47.56 KiB) Viewed 12920 times

The planning for this engine startet quite a while ago. The goal was to make a simple alpha stirling witch is able to produce some power. First i was going with an open Crank drive. Later on I decided to put a Housing around de Crank mechanism, because i want to try pressurization on this engine too.

[youtube]https://www.youtube.com/watch?v=DbgKKAVHCcY[/youtube]

This Video shows the very first runs of the engine. It's my best performing engine so far.
The engine has a bore of 32mm and a stroke of 16mm. The crank angle is set to 90°. The Pistons are of the clearance type made of cast iron and running in steel cylinders. The clearance of the pistons is 0.01mm and they seal pretty well.
To keep things simple, the engine does not have a regenerator except the annulus around the displacer. The Cooler consists of a set of slots machined in the cover plate.

Right now I'm building a Prony Brake to measure the power output. I'm really curious how much it will be.

Any Questions, Comments and suggestions are welcome

Plani

[Aviator168]

Very nice. What is the power output?
About cooling. Why was jacket type cooler use?

[PlaniTechic]

Thank you.
I don't know the power output yet. The prony brake is not yet finished, my trusty old mill broke just when I started to make parts for the brake.
I don't quite understand yout question abaout the cooler?
What did I do wrong with my post? I was expecting the video to embed?!?! But instead I can only see the link. Does anybody know how I can fix that? Thanks

Plani

[PlaniTechic]

After the first couple of testruns the engine was taken apart and given a thorough cleaning. The expansion piston showed some slight signs of rubbing and was therefore polished a little bit more. As a result there were some more rpm

max rpm.jpg (73.81 KiB) Viewed 12888 times

Another thing that I didn't expect was, that if I close up the engine casing it's loosing about 200rpm. I think these are pumping losses. I'm wondering now, how this will affect the engine once it gets pressurized?

Cheers
Plani

[Aviator168]

You need a valve to balance the pressure between the crank and the engine when the engine's internal volume is largest. This is also the mechanism to pressurize the engine which is by pumping more gas into the crank case.

[PlaniTechic]

Hi,

Yes, thats what I figured out as well.

WP_000482 (640x480).jpg (159.11 KiB) Viewed 12865 times

This is the Valve I tried. The thread on it is a M2, so it's rather small. It's buit into the block which is holding the wrist pin of the conrod in the compressiomn piston. I was thinking the solutin with the O-Ring schould be ok, but it didn't work well. I was not able to adjust the thing. So it was either not opening at all or it was blowing by on the upstroke.
I'll have to come up with something else....suggestions ar very welcome

Plani

[Aviator168]

The simplest would be just connect a small tube from the cold cylinder ( at the location when the piston is at BDC) to the crank. Don't need any spring at all unless you plan to move the location of the valve to different places in the future to have difference engine speeds like an ICE. Just curious, where are you placing the valve?

[PlaniTechic]

Hi,
So you basically suggest something like a port on a two stroke engine? I've never thought of that. That sounds interesting. Although on a second thought, i'm not sure if this woud be a good solution. When the cold piston is at its BDC, the volume of air on top of the pistons is not at its maximum. This occurres with the cranks at 45° (assuming 90° between the cranks as it is in this case). So the pressure on top of the pistons isn't at its minimum (at least in a cold engine). With the engine hot and running i think the whole thing looks different again. So for now I will stick with some pressure driven valve which will let some additional air in to the engine as soon as the pressure on top of the pistions is smaller than in the crankcase. Althoug it might be an external valve. The one in the picture above is built into the center of the cold piston, but for now it's just closed.

Plani

[Ian S C]

You beat me to it, I was about to mention that to equalise pressure, all that is required is a small transfer port that is exposed as the piston goes to BDC. For an atmospheric motor a snifter valve is worth a try, the simplest form is a leather cup seal on top of the piston, this also allows an even looser piston, and the cup seal works like the cup in a bicycle pump.
Ian S C

[PlaniTechic]

Hi there
It's been a while. But today I was doing some tests on the Engine with the Prony Brake:

[youtube]https://www.youtube.com/watch?v=jvERRg9P2IM[/youtube]

(Just in case it won't embed again, here's the link too: https://www.youtube.com/watch?v=jvERRg9P2IM )

Prettymuch on the first Try the little 18cc Engine was able to put out 8W. I'm pretty pleased . As it's written in the literature for a Hot Air Type Engine it can be expected to get 0.5W per cc. So I'm getting close . Although I had to leave open the back cover of the crankcase. Otherwise roughly 1W is eaten up by pumping losses. There is also some other strange behaviour as it can be seen in the Video after shutting off the burner the engine stops almost immediately, althoug the heater head is still glowing red. Somehow the Engine looses compression once it gets relly hot. Right now, I have no clue why it does this ...
Next up, I need to get the snifter valve working to see what this does to the power output.

Plani

[burnit0017]

Wow, great results. Thanks for posting. Are you using a water jacket on the cold cylinder?

[PlaniTechic]

Hi burnit0017

The Engine is actually water cooled, but there is no water jacket on the cold cylinder. The cooler sits on top of the cold cylinder. From there it cools the air passing throug the slots machined into the top plate bewtween the two cylinders.

Plani

[PlaniTechic]

Hi

Today I got the snifter Valve working. The design was changed from the O-Ring to a poppet-valve.

DSC01617 (640x480).jpg (141.5 KiB) Viewed 12450 times

The valve was working nicely. The Air could be heard, as it was taken in on the downstroke of the cold Piston. I tried then to start the engine again, but somehow it was hard to start and once running it behaved erratic. This puzzled me quite a bit, since i was expecting some more power with the snifter in place. I then found out, that the flywheel wasn't tightened properly on the shaft which was causing this behaviour.


After that the engine started again nice. I was just about to start another run with the Brake when Desaster struck

DSC01629 (640x480).jpg (221.66 KiB) Viewed 12450 times

DSC01631 (640x480).jpg (250.65 KiB) Viewed 12450 times

The Valve lost its retainig nut and got jammed up between the piston and the cover plate. That din't sound good
The valve was broken. The cover plate got some hits too. And the valve seat in the holding block of the pisten got smashed as well. Luckily the Piston and the cylinder survived with no damage.

So its back to the drawingboard. The valve would actually work, I just need to come up with a better solution wich does not turn itself loose.

Plani

[tew]

Plani, really really nice engine. But I guess I don't understand your displacer cylinder. Looking at the cutout dwg. the piston appears to be very thin. I thought the displacer piston should be almost half the length of the displacer.

[Ian S C]

I presume that the top of the hot piston is in the form of a Heylandt Crown, Do you know the correct ratio, diameter to length that it should be, I looked all over for it when I built my Ross Yoke motor. The cooling system on my motor is a jacket around the bottom of the hot cylinder, and another around the cold cylinder. Under normal running the cooling system is not used, This motor has a bore of 30 mm, and a stroke of 20 mm, and has a similar power to your motor, but your motor wins hands down on looks.
You may get a wee bit more power out of it by improving the cooling system, it's equally as important to cool the motor as it is to heat it.
An experiment that you can do, get a motor that you can link to your Stirling Engine, and run it in the normal direction, and see what temperature you can get the hot cap to, mine went to minus 20*C in about 20 minutes.
Ian S C