Request Advice - Gamma Stirling

[Hawke]

Well all attempts so far have failed. Some engines have been dismantled using parts, others await renewed interest. I seem to like trying new styles when I get to that frustration point on the project. My latest now is what I think is called a Gamma Stirling of sorts.

A work in progress still here... Ive been in a keen attention mode this time to precision and smooth actions. My displacer is the best Ive done so far and I have high hopes for the power diaphragm. Utilizing an older flywheel, the best in precision Ive done so far, Ive left the crankshaft idea I had at first. Displacer rod is 1/16 brass through a 3/32 brass tube. Bottom of rod has triangle spread which is epoxy glued to a strip of pop can aluminum. Should with stand the heat I think. Bottom of the displacer is a soup can which will be filled with high temp silicone as will the transfer tube between the two cylinders.

My main concern is the size of the cylinders and strokes.
Displacer size - 3" long with 1/16" gap to cylinder and glued with epoxy together so its very smooth acting
Displacer Cylinder - 4 1/2" long (beer can)
Power Diaphragm - Helium Balloon, 1" ID toilet PVC connector slide onto straight PVC pipe glued into the frame
Displacer Stroke - 1/2"
Diaphragm Stroke - 7/8"

I'v read so much on ratio's and stroke but seems the diaphragm style power use throws things off. I watched many a YouTube video looking at sizes of components which is overwhelming a bit. That part of the deal I find is quite critical but I have no experience with working engines therefore nothing to experiment on. Your thoughts on this part especially is welcomed.

[Hawke]

Sealed Up! er.... I hope.
On to the flywheel and crank. Worried that my power cylinder is too long. Might take more flow that the displacer will provide to get it to move sufficiently. Shouldnt be too hard to modify if needed.

[fullofhotair]

What I do is work around the power stroke. You can measure this on a ruler by pull up the diaphragm with the connection rod, take that height of the con rod, then push down, take that measurement, subtract= power stroke. Then remember the displacer stroke has to be 1.5 longer than the power stroke. So if you got a measurement of one inch, you would know the bend in the crankshaft bar would be 1/2 inch, cause the crankshaft bar turns up the down equaling one inch. so now you know your bend for the displacer is going to have to be 3/4 of an inch .Since the up and down will equal 1.5 inches .Everything else looks good. Make sure you have the right weight flywheel. To light and it will tend to stall out on each cycle. like it needs help to make it around. To heavy and it will do fine once you spin it but then lug out trying to turn to much weight.

[fullofhotair]

PS
After taking another look at the picture of your engine, you might have to much dead space in your power piston cylinder. Ideally all the space you should have is enough room for the diaphragm to move down without being stopped. It might work this way but youll loose a lot of possible power. Also I forgot to add when you do your displacer make sure the you leave like an 1/8 of inch extra clearance at both the bottom and top of the pop can so the displacer doesn't bang up against the top and bottom.

[Ian S C]

The 3/32" tube that the 1/16" displacer rod passes through is a bit much of a gap, a 1/16" rod only needs a 1/16" hole opened out about .001". Ian S C

[Hawke]

Thx so much guys. Ian, the 3/32 tube measurement is "OD" and the inside is quite tight against the 1/16 rod. Work has me stretched out still, but I have a 3 day weekend coming up to ponder over the comments and utilize them.

[Hawke]

First attempt failed however I'm pleased with the mechanics Dry run video. Displacer tapped the bottom once but thats an easy fix. Left it in video so you can adjust your sound. You will find its pretty quiet and smooth running. I need to do a leak test somehow. How can I do this besides soapy water maybe? I added weight to flywheel. I'll get some more close-ups of the displacer rod and sleeve asap.

Leaks is first troubleshooting task as I dont see any pressure in the power diaphragm under heat. The power cylinder may be too much dead space as you mentioned fullofhotair.

[youtube]<iframe width="640" height="360" src="https://www.youtube.com/embed/uuIz0IDHr ... detailpage" frameborder="0" allowfullscreen></iframe>[/youtube]

https://www.youtube.com/watch?v=uuIz0IDHr-M

[Hawke]

Hurray!! It runs!

I had forgotten to seal the Diaphragm Casing to the inner PVC. 5min epoxy did the trick. Tea lamp does not provide enough heat, however my little mircro torch does. I'll have to build a low profile alcohol jet burner for it.
http://www.youtube.com/watch?v=6WpB9B7PKuo
Question: How much temperature do you think this guy can stand? I was really surprised how hot even the top cooling end of the displacer cylinder gets.
Heated it a bit longer and it ran several rpm's faster, with a little chuck of ice even more, but Im afraid to overheat and ruin it. So I havent found its potential rpm at the current construction. I always planned a water cooling device and it looks like it might have enough power to run one.

[Hawke]

Some experiments done with different heat sources and ice added. The syringe in this video is a check valve for the cooling system which is an ongoing work in progress at this point. Hope the engine can carry the pump load.

https://www.youtube.com/watch?v=5TycrOca7sk

[Ian S C]

Hawke, you don't need any power the "drive" a cooling system. Get a can say about 1" larger in diameter than the displacer, and about a inch high, cut a hole in the bottom to fit over the displacer cylinder, glue it on, on top of the plastic tube. You will need an extension on the displacer rod outlet tube, so that it is above the cooling can, this could be a bit of plastic tube similar to the tube of ink in a ball point pen, or even the body of the pen. Fill that with cold water, and see how it goes. A larger diameter can and you could put the can under the plastic elbow, just make sure the diaphragm, and the displacer rod outlet tube are above the water level. Ian S C

[Hawke]

[tab=20]Thx Ian. Ive seen those set ups but I wanted a more closed self contained system which re-uses the same water after cooling it. Ive gotten thru the first trial to see if my check valve creation would work. Its drips is about all so far. I do plan to have the can above displacer cylinder as you spoke about. This style is why I was saying it would take some drive power.

[tab=20] I did see a design on YouTube that uses the pressure created to the power cylinder and they said it didnt take much power from the engine. It uses a diaphragm. Another design I may try is with flapper rubber check valves. I dont see the need for double check valves in this style Im doing now though.

http://www.youtube.com/watch?v=hJFgy3d6S8E
Trying a design here similar to approtechie's. Needs a better check valve for one. The finished design will have coolant water dumped onto top of displacer cylinder. Also a ice can that the copper coil sits in.

[Hawke]

[tab=20]Ive got the same basic design doing twice as good by moving the check valve(ball bearing inside syringe) to the bottom requiring less suction to start the siphon assistance. It now does about two drops per second. This might be adequate if I can provide an "ice can" for the copper coil to sit in. This Stirling is not a real high speed capable design I guess. It appears Ive reached the limit of RPM's this engine can do. I am pleased with its performance considering its my first running one. The tweaking fun has begun tho to see what all I can learn with this one.

[tab=20]Copper has a high heat dissipation transfer rate but glass and plastic does not. I wanted to be able to "see" any movement if the system would work first. I plan to use more copper or brass in the final version for the cooling effect. A fan would be nice but I haven't looked into that yet much. I know I have more lessons to come with this one before its time to try another. Sure is good to be able to do some experimenting. My bottom of displacer cylinder is showing some deterioration around the high temp silicone seal. Ive got to get a small alcohol burner made which may provide a heat source better than the 3 tea lamps but not as extreme as the mirco torch. It can make the tin bottom red hot in a matter of seconds which you might have noticed in one of the videos. I think the silicone is rated for 650 degrees tops.

[fullofhotair]

Hawke,
A good alcohol burner is easily made out of a pop can.
http://youtu.be/qj7PIhjPLxA
You said you were thinking about a fan. You pretty much have what you need already. You have a flywheel just replace it for a small plastic fan blade off a dead fan. The fan now serves two purposes, flywheel and fan. You really dont need a pump. Google thermal syphon.The hot water taken off the cooling end of your engine rises in a tube to a closed reservoir. The cooler water in the bottom of the tank falls back down to cool the engine. If you place a copper tube radiator in front of the fan it becomes faster and colder return. you can cut strips an inch long down a pop can . Then make holes ever inch or two down the strip.You thread your copper tubing through these strips to make fins for your radiator. If you havent bent much copper tubing ,there is a trick to avoid cripping. Fill the tube with sand or gravel and cap it off at both ends before bending.

[Hawke]

Very cool points Full! Fan flywheel combo I like. Possible those Radio Shack fans with wire coils could be utilized and provide a generator to. However, generators would be best made with a free piston style engine In my opinion.

Now on this thermosyphon system I like the simplicity and lack of needing power, but Im feeliing it wont deliver the "ice cold" temps Im wanting. Seems that the closer to ice temps I can get even if some power used would deliver more rpms in the long run that the thermosyphon. Visualizing does always provide actual results that can be attained though.
This one:
http://www.youtube.com/watch?v=2t5iJB4mSV0
works for sure but as it is there its no where near what I want to achieve. Running any design it thru a ice filled can might be my best bet. Please expand on any cooling designs you guys have seen.

[Ian S C]

Most of my larger motors use thermosyphon cooling, the water in the reasonably small radiators that I use, usually stays a bit bellow boiling, and the motors will run all day if needed, some times needing a top up with water. One motor uses a pump, it's not doing too well at the moment, but the pump should be pumping 2L a minuite, and if it pumps the water from the 2L container that it discharges into, the water temp increases by about 10*C over the days running.
One cooling system I heard of was designed to solve two problems. The gas cylinder was getting too cold, and the water was getting too hot. So the gas cylinder was put in the water container, it was a bit of a balancing act to stabilise the temperature, too hot and the gas pressure goes up, the engine gets hotter etc etc. Ian S C