low temp Stirling help

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low temp Stirling help

Postby luka1222 » Sat Feb 28, 2009 9:26 am

Hello guys, i have recently completed building in my own low temp
Stirling from scratch. I am a complete beginner and havent read
anything on how to make one but i understand them pretty well. my
problem is my engine doesnt run very well at all and i need some
pointers as to why. i have got it to run twice on a mug of boiling
water but it ran very slowly around 20-30 rpm and it only lasted a few
minutes if that, it kind if looked like it was struggling. now i cant
seem to get it running again


my engine is made from a 100mm diameter acrylic tube 15mm deep
sandwiched by two aluminum plates.the rest of the engine is made from
brass. the power cylinder is around 11.6 mm diameter and have a
accetal piston that i am confident is a very nice free running fit. in
fact the whole thing i am very confident that is is sealed and
airtight. the displacer piston is made from 3mm thick foam board and
is offset of the crank accordingly. the power piston is offset off the
crank by around 4.5mm. this came from the only piece of info i had
from somewhere that said the volumes of the power cylinder sound be
100 times smaller than the main chamber, is this correct?.
the flywheel is around 95mm diameter and runs off good bearings, as
does the rods that connect the pistons to the crank. the only thing
that i haven't done properly yet is balance the whole thing, the
weight of the displacer piston is basically balanced but the weight of
the power piston is not at all and the flywheel my be off slightly.
one thing i noticed looking at pictures on the internet of other
models the displacer looks thicker than mine foe around the same sive
chamber, is this important?

i would appreciate any hints and tips and will try to get photos and
maybe a movie once i get it running ok. thanks in advance.
one thing i noticed
luka1222
 
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Response to low temp Stirling help

Postby sgraehl » Fri Mar 13, 2009 8:41 pm

Help has been a little time getting here but from what you have described, I would say your displacer should be thicker. The type of LTD gamma you have made usually has a displacer that is 50% of the thickness of the displacer chamber. I'm not sure what you mean by "offset" but the displacer should lead the power piston by 90 degrees. This amount can be played with a bit to "tweak" your engine after you have it running if you have made it adjustable. Your engine should spin freely by hand half a dozen or so complete turns with a "flick". Look for any binding by slowly turning engine over and feeling the slight play in you connecting rod linkages. Lastly, you should be able to feel some compression as the power piston goes down, a very small amount is desired in an LTD. If there is alot of compression, it will take more heat to run. Get your displacer thickend and leave a couple milimeters side clearance, make sure it just reaches it's full stroke without bottoming or topping out (more places of binding)and a good guess for power piston stroke with your demensions would be about 7 mm. As for cylinder size ratios, your engine should run. LTD's like pretty excessive ratios unlike the usual machine made gamma's you see. Those usually use a 1.5 to 1 cylinder ratio (displcer larger than power cylinder)and take more heat to run.
sgraehl
 
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