My first stirling... on the brink of failure. HELP!

[matador]

This is my first attempt at a stirling engine. I cant get it running and am very frustrated. I followed the plans on this site.
http://astro.sfasu.edu/courses/egr112/S ... rling.html
This is what it looked like when I first tried to get it running.

stirling.JPG (133.82 KiB) Viewed 11436 times

Then trying to get it running a made some modifications.

modified.JPG (140.74 KiB) Viewed 11436 times

Ive tried everything I can think of. The crank runs very smooth, as does the displacer. Ive tried different things for flywheels and placed counter balance weights in a million different spots on the flywheel. The displacer is air tight, no lease in the pressure vessel. ive played with the elasticity of the diaphragm. Im hoping that my lack of knowledge and inexperience with stirlings is making me overlook something very simple. I need to get thing going!!! Can anyone please help

[Junkie]

A few questions : Does anything at all happen when you heat it up ? Do the cranks turn just a little? What heat source are you using?

[matador]

When I put heat to it nothing happens.. I use about 4 tea lite candles, with ice on top. I think heat might be my problem. I think my fire box or whatever its called, is to tall. The site that I found these plans say to make the displacer out of aluminum cans making an air tight cylinder, every other set of plans I see that are for can engines use steel wool. Could that make any difference??

[matador]

and just so you know I took lots of pictures throughout the entire build, so if there is anything you need to see I can post pics.

[matador]

My displacer is made out of the bottoms of two soda cans. After the JB weld set up I tested for leaks by dipping it into my hot tub. This is about the best picture I have of it.

displacer.JPG (104.17 KiB) Viewed 11418 times

[jimlarsen]

Here are some trouble shooting tips: http://sites.google.com/site/stirlingbu ... oting-tips

The fundamentals are:
Temperature Differential (It sounds like you have that)
Low Friction (It sounds like you are OK with that)
Pressure Leaks (There should be almost none.)
Crankshaft Phase (Does your drive cylinder follow 90 degrees behind your displacer as the crank rotates?)
Direction (The SFA engine only runs in one direction)

I always set the balloon diaphragm so that there is only enough slack for the engine to rotate. If you make it tighter, you create lots of friction. If you make it looser, you lose power.

Here is a test you can do. Disconnect the drive diaphragm connecting rod. Apply heat and ice as you normally would. Manually rotate the crankshaft so that the displacer moves up and down. Watch the diaphragm and see if it is moving up and down with each cycle. If it moves when it is not connected, then you are getting some power. You may be able to work from there to trouble shoot what the problem is.

The air tight displacer is an issue of some dispute. It works best if it is air tight, but it works OK if it is not. I have built the SFA engine and it still works. I started with an air tight displacer. Then it overheated and the displacer burst, but it still works.

[Junkie]

Most of these SFA engines that don't run, are not running because the displacer bushing is too loose, so it leaks a lot. Have you tried submerging it in hot water to see if there are any air leaks?

[Doogle]

Do we agree that the displacer / pressure vessel ratio is correct in the plans? They go for quite a small displacer for the size of the pressure vessel.

[matador]

I don't think my displacer bushing is too loose. The way its designed there is going to to be very small pressure leaks there. As for the displacer/pressure vessel ratio with the SFA plans the displacer seems to be close to half the volume of the pressure vessel. What would be the most efficient ratio for this?

Ive modified my fire box, made it quite a bit shorter. Once the JB weld set I'll test it again and see what happens.

[jimlarsen]

The most important measure of the displacer is swept volume. It must travel almost the entire length of the pressure vessel. The SFA plans call for 1/8" of clearance at each end of the stroke. The picture of your displacer makes it look quite short. If your stroke is too short you end up with a lot of dead space and that kills your power.

[matador]

Well Jim, I think your right.. I might have to adjust my crank. It seems that when the displacer reaches its highest point on the crank that there is a lot of dead space above it. I did get it run, but I have to use a torch.

Here's a link to some video of it running, maybe this can help you understand a problem..

http://www.youtube.com/watch?v=hkqgYPCdRhE

[jimlarsen]

I looked at the video and observed a couple of things. First is that your counterbalance is too heavy. It is intended to counter the weight of the displacer. The flywheel should be in better balance when it is the right weight. I often use a penny or similar small coin. Place it opposite of the displacer.

The second thing I notice is that your crank is not directly over the displacer shaft. Pulling to the side like that introduces friction. These engines barely have enough power to overcome their own friction, so you must be extremely vigalent in controlling it.

I could not tell from the video if the diaphragm was too tight, but that is sometimes an issue. If the engine has to stretch the diaphragm as it runs, that consumes power. It is best to adjust the diaphragm carefully so that there is no stretching required, and no surplus slack. It is a fine line.

I think you will soon have it working with just a little more adjustment and fine tuning.

[matador]

well I think I have made too many modifications to this engine. Its staring to look quite ugly with cans that have been jb welded on then cut off then other cans welded on. Its time for another build. I do have a few questions though... I see a lot of displacers made of steel wool, is there more power when using steel wool? And I think instead of following plans I'll just try to wing it and come up with my own design. I have this aluminum water bottle that I want to use as a pressure vessel. Its about 7" tall. How big of a displacer should I use? and does the size of the diaphragm really matter much? And as for keeping a crankshaft in place, I see a lot of designs that use what they call an "electrical terminal connector", where do you get those? And where cam I find those small bearings that have the inside diameter close to the size of a coat hanger? And if I post a sketch of my new design can you help make suggestions?

[jimlarsen]

7 inches is probably too tall to be practical. You will want to shorten it a bit. At that length your displacer will either be long and heavy, or it will have to travel a long distance.

I haven't made a steel wool displacer, but I see them working well. They double as a regenerator. They are easier to make, but I think they may deteriorate with use. Steel wool tends to fall apart with vibration.

I build my can engines with a displacer that is 1" shorter than the pressure chamber. I make the crank shaft with a 3/8" offset so that the displacer travels 3/4", leaving 1/8" of clearance at each end of the stroke.

If you want something to hold the crankshaft in place you can get Shaft Collars for about $0.50 each at the hardware store. You can also find them online at Amazon.com and other sites. Search the web for Shaft Collar and you will see lots of options. I find it is a lot faster to just twist a short piece of wire on the shaft. You won't always need to stabilize the shaft. If you have good alignment the collars aren't needed. It has a lot to do with luck! :-)

I have learned that it is just as easy to make two engines as it is to make one. So when I make a can engine, I usually make two at a time. I figure I am improving my odds for success. But so far they have always both worked.

Look through the list of videos at this link and you will see several can engines. http://www.youtube.com/16strings

[matador]

You have some awesome engines on your youtube channel! The two can engine on your front page I noticed that the diaphragms (that's the drive piston right?) are coming out of what looks like the middle of your can. Can you put those anywhere on the pressure vessel?