Trying a Stirling
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Is the flywheel steel? If so, it's definitely heavy enough.
undo the tube from power piston but leave on at displacer end, take displacer assembly off (leave displacer and rod in) submerge it all in water and blow into the tube. There should be no bubbles. Maybe the odd 1 or 2 from around the rod but basically no leaks.
Friction wise, with the hot cap off the engine should spin over for about 20 revolutions from a flick of the flywheel.
Looks great.
Nick
undo the tube from power piston but leave on at displacer end, take displacer assembly off (leave displacer and rod in) submerge it all in water and blow into the tube. There should be no bubbles. Maybe the odd 1 or 2 from around the rod but basically no leaks.
Friction wise, with the hot cap off the engine should spin over for about 20 revolutions from a flick of the flywheel.
Looks great.
Nick
dgjessing
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I've fooled around with a bit more and it's getting closer, but still no cigar.
The flywheel has an aluminum disk with a steel rim. Don't have it in front of me but I'd guess the rim is about 3/8" wide and 1/4" thick (3" schedule 40 pipe). It's probably just fine.
I think I'm doing pretty well air-tightness wise - with the rod disconnected from the crank, if I abruptly shove the piston to the bottom of the cylinder it pops back about half way.
It's nowhere near that good friction-wise - it might spin 5 times, but nowhere near 20... The crank and flywheel alone may go 10 times :-[
I've ordered some little ball bearings to use in a new main bearing assembly.
The flywheel has an aluminum disk with a steel rim. Don't have it in front of me but I'd guess the rim is about 3/8" wide and 1/4" thick (3" schedule 40 pipe). It's probably just fine.
I think I'm doing pretty well air-tightness wise - with the rod disconnected from the crank, if I abruptly shove the piston to the bottom of the cylinder it pops back about half way.
It's nowhere near that good friction-wise - it might spin 5 times, but nowhere near 20... The crank and flywheel alone may go 10 times :-[
I've ordered some little ball bearings to use in a new main bearing assembly.
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Did it have ball bearings before or just sleeve bearings? These engines definitely need ball bearings to minimize friction as much as possible. Hang in there, it sounds like you are close.
Bill
Bill
dgjessing
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Plain brass bearing with a steel shaft currently. I've ordered a couple of 1/4 x 3/8 x 1/8 ball bearings and I'll make a hub that uses those with the existing crank.
I just made a neat looking sheet metal hood to go over the hot end and (theoretically) hold the heat around it better. Looks nice anyway ;D
Seems like it's really close to running... It's to the point where it will pick up a little speed just after tdc or bdc but still not follow through. With any luck the better crank bearings are what it needs!
I just made a neat looking sheet metal hood to go over the hot end and (theoretically) hold the heat around it better. Looks nice anyway ;D
Seems like it's really close to running... It's to the point where it will pick up a little speed just after tdc or bdc but still not follow through. With any luck the better crank bearings are what it needs!
If the leak test as I described (not power piston but the displacer assembly) is ok, it must be friction that is the enemy. It doesn't sound anywhere near free enough yet.
The crank and flywheel disconnected should spin over for many revolutions, for 20 seconds plus - it sounds extreme but you will find if you use the ball bearings it will do that.
The other thing you mentioned about the piston springing back is good in once sense, it shows there's a good seal. What is the bore and stroke of power and displacer pistons if you don't mind me asking? If it's springing back too much, it could mean the ratio of the two swept volumes is too small. This happened when I designed mine and I ended up making the displacer bore larger, I also made the displacer longer to minimise heat transfer from hot to cold end.
Sounds like you're nearly there. Have you tried a drop of light oil on piston and displacer rod?
Cheers
Nick
The crank and flywheel disconnected should spin over for many revolutions, for 20 seconds plus - it sounds extreme but you will find if you use the ball bearings it will do that.
The other thing you mentioned about the piston springing back is good in once sense, it shows there's a good seal. What is the bore and stroke of power and displacer pistons if you don't mind me asking? If it's springing back too much, it could mean the ratio of the two swept volumes is too small. This happened when I designed mine and I ended up making the displacer bore larger, I also made the displacer longer to minimise heat transfer from hot to cold end.
Sounds like you're nearly there. Have you tried a drop of light oil on piston and displacer rod?
Cheers
Nick
SignalFailure
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I made a simliar (though rather more, ahem, agricultural) version of this type of engine...no plans just winged it but it wouldn't run 
I posted it on the stirling forum here http://stirlingengineforum.com/viewtopic.php?f=1&t=448 - sorry my picture has been removed but the follow up post might give you some clues to get yours going. Good luck, nice work deserves to run!
EDIT: ah, I found the picture...
I posted it on the stirling forum here http://stirlingengineforum.com/viewtopic.php?f=1&t=448 - sorry my picture has been removed but the follow up post might give you some clues to get yours going. Good luck, nice work deserves to run!EDIT: ah, I found the picture...
dgjessing
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Thanks, Nick - the displacer bore is 3/4", the power cylinder 1/2", and the stroke for both 3/4". The displacer is 1 1/2" long and comes to within 1/8" of the ends of both the hot and cold ends of the cylinder (depending on which end it's pushed/pulled into). I don't know if you noticed or not but I cut threads all the way through the cold end on the theory that would help with heat transfer, and the hot end is insulated from the cold with several turns of teflon tape.
Thanks for the info. How much clearance does the displacer have around it? Mine has about 1/32" so the displacer piston is 1/16" smaller diameter than the bore.
I think your displacer bore / piston is a little on the small side, even if you have 1/32" clearance all around like mine, it means your displacer swept volume is very similar to that of the power piston. It might be worth trying putting ice cubes on the cold end whilst attempting to run - having that ratio closer to 1:1 makes for an efficient engine but it means you need a higher temperature differential. If it runs with ice, you may need to make your displacer swept volume larger - the only way will be to bore your displacer cylinder out, new displacer and new hot cap. Note, the clearance at each end should be small too, same as the sides, about 1/32" is sufficient.
If you have no leakage on the displacer end, the only other problem would be friction. If it's trying now, the bearings may sort it so that would be the first thing to try. Does your power piston (with bottom off power cylinder) fall through the cylinder under its own weight? If so, it should be ok, if you put your thumb over bottom of cylinder and try to push piston in, there should be strong resistance from a sealing point of view - (sounds like you're ok on that front)
On mine it was leakage. The water jacket on mine was an after thought, I got it running on ice cubes initially, then water but now I've sorted the leaks I think it should run without water - can't remember whether I've tried. Could try tonight.
Hope this helps,
Nick
I think your displacer bore / piston is a little on the small side, even if you have 1/32" clearance all around like mine, it means your displacer swept volume is very similar to that of the power piston. It might be worth trying putting ice cubes on the cold end whilst attempting to run - having that ratio closer to 1:1 makes for an efficient engine but it means you need a higher temperature differential. If it runs with ice, you may need to make your displacer swept volume larger - the only way will be to bore your displacer cylinder out, new displacer and new hot cap. Note, the clearance at each end should be small too, same as the sides, about 1/32" is sufficient.
If you have no leakage on the displacer end, the only other problem would be friction. If it's trying now, the bearings may sort it so that would be the first thing to try. Does your power piston (with bottom off power cylinder) fall through the cylinder under its own weight? If so, it should be ok, if you put your thumb over bottom of cylinder and try to push piston in, there should be strong resistance from a sealing point of view - (sounds like you're ok on that front)
On mine it was leakage. The water jacket on mine was an after thought, I got it running on ice cubes initially, then water but now I've sorted the leaks I think it should run without water - can't remember whether I've tried. Could try tonight.
Hope this helps,
Nick
dgjessing
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Thanks Nick - I really appreciate it!
If the ball bearings don't do the trick I'll make the displacer piston a bit larger in diameter and longer on both ends.
I didn't get into the theory behind these things at all when designing it - I just looked at some other plans and guessed :
I have tried putting ice on the cold end during my attempts to get it to run - my impression was that it didn't help much (but what do I know?).
While waiting for the bearings to arrive I'm making an adjustable height pillar for the candle to sit on.
If the ball bearings don't do the trick I'll make the displacer piston a bit larger in diameter and longer on both ends.
I didn't get into the theory behind these things at all when designing it - I just looked at some other plans and guessed :
I have tried putting ice on the cold end during my attempts to get it to run - my impression was that it didn't help much (but what do I know?).
While waiting for the bearings to arrive I'm making an adjustable height pillar for the candle to sit on.
No problem, you'll have it sorted soon.
I didn't consider these things enough at first either, hence modifcations down the line.
I think you may have just answered part of the problem though - again one that I encountered. I originally designed mine to be run from a tea light but I quickly realised / was advised that there is very little heat in a candle - not enough to run an engine like this. You need a meths burner with a fairly large flame that sort of wraps itself around the hot cap - look at mine again, note the blue flame from the meths- much hotter than a candle flame.
So I'd try, proper burner, bearings (I still think you'll need them judging by the friction test) then final resort the displacer bore. Increasing the diameter is the only way you can increase that swept volume on an engine in this configuration but it's the best way anyway as it's a squared relationship.
I think you're nearly there.
Nick
I didn't consider these things enough at first either, hence modifcations down the line.
I think you may have just answered part of the problem though - again one that I encountered. I originally designed mine to be run from a tea light but I quickly realised / was advised that there is very little heat in a candle - not enough to run an engine like this. You need a meths burner with a fairly large flame that sort of wraps itself around the hot cap - look at mine again, note the blue flame from the meths- much hotter than a candle flame.
So I'd try, proper burner, bearings (I still think you'll need them judging by the friction test) then final resort the displacer bore. Increasing the diameter is the only way you can increase that swept volume on an engine in this configuration but it's the best way anyway as it's a squared relationship.
I think you're nearly there.
Nick
Hi, i remember the joys of ironing out very similar problems with my first stirling, it has seperate cranks for displacer and power piston, and the crutial factor with it was timing, a few degrees either way and it wont run. But mine is prehaps exception to the rule as it also requires the whole thing (all of the displacer and some of the frame) to be hot before running fast, very bizzare but true all the same. Here is a picture, irt was the very first thing i machined so please excuse the charecterful (rough!) machine work, good luck with your engine, you seem very close James.
Course it counts, it runs! :bow:
Is that with the new bearings or without? Just some fine tuning to do now, the timing can't be out, that's one thing you don't have to worry about with this layout!
I think this was the point when I discovered that there was a leak around the hot cap on mine and the pillar where the transfer port was drilled so I needed loads of ptfe tape to give a good enough seal.
If yours has no leaks and still requires the ice, it must either be friction, or the displacer is too small or a combination of the two.
Well done!
Nick
ps snap - can't remember if I've shown this before!
[ame=http://www.youtube.com/watch?v=xAgzQroi6PE]http://www.youtube.com/watch?v=xAgzQroi6PE[/ame]
Is that with the new bearings or without? Just some fine tuning to do now, the timing can't be out, that's one thing you don't have to worry about with this layout!
I think this was the point when I discovered that there was a leak around the hot cap on mine and the pillar where the transfer port was drilled so I needed loads of ptfe tape to give a good enough seal.
If yours has no leaks and still requires the ice, it must either be friction, or the displacer is too small or a combination of the two.
Well done!
Nick
ps snap - can't remember if I've shown this before!
[ame=http://www.youtube.com/watch?v=xAgzQroi6PE]http://www.youtube.com/watch?v=xAgzQroi6PE[/ame]
