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I'm a senior Mechanical Engineering student in Baskent University,
Ankara-Turkey. My final project is building a Stirling engine. I
chose a gamma type Stirling engine and built it. Unfortunately,
engine does not work. I tried many times but i am unable to make it
work. In design process i chose the work piston stroke 20 mm,
displacer stroke, 8,5 mm displacer diameter 168 mm work volume
diameter 172 mm (which makes the clearence between displacer and
work space wolume 2 mms). My dead volumes are nearly 1 mm from top
and bottom surface and also i made a different displacer with same
diameter and height of 12mms which is made of wood and have dead
volumes of 5 mm from both surfaces. I tried both of them but engine
did not respond.

I have some questions about this situation.
1) what is the importance of displacer? (I mean the weight of the
displacer is important or not.) Also are dead volume heights are
important for me? (For my engine what is the optimum dead volume
height.)
2)is The clearance value between displacer and work volume wall an
important parameter. What should it be for my engine?
3)I am unable to process the cylinders perfectly so there are some
sealing problems. I used a rug(i am not sure is this the correct
word but i mean something for seal) but it causes friction losses.
For gamma types is friction a big problem and can it be the reason
for not working. Also is sealing important or can it work with a
small gas escape.
4) Last question is about dimensions. I gave you my dimensions
above. Could it be a reason for not working. I also want to add that
my maximum temperatue is about 120 celcius.

I would be very happy if you could answer my questions.

Thanks...

hi
The weight of the displacer may effects on engine balancing, it is better to have both pistons with same weight.

Good for you, for being so ambitious with this project. I hope other jump and and help you, even correct me, I don't care.

The word you used "rug" I am pretty sure you mean "ring" as in a piston ring. Common usage in Stirling designs use graphite type rings, or even the whole piston made out of it. It is even better to have loss past the rings, but you can not have more the the smallest friction possible.

The goal is an engine that spins, but really has no power, not even enough to overcome its own small friction values. I believe I do know the core answer to how to build a "modern" Stirling, if my new cycle can even be called that anymore, but that is another story.

The best of luck to you.