Stirlingengineforum.com

Greetings all. Complete noob here. I'm very excited to have found the forum. For quite a while I considered taking on a project and decided to bite the bullet. Please forgive me but at almost 50 I have found myself trying to re teach myself high school physics, which I did not do well, to muddle my way through a first time, beginning project. I found an interest in another poster's "glass engine"

https://stirlingengineforum.com/viewtopic.php?t=2045

I was curious if anyone would know how his displacer held up over time and if this design may produce enough torque to turn a light fan blade? I would be interested in replicating this with the possibility of eventually making a wood stove fan. Alternative displacer material is of interest. This seems to be a highly discussed topic but if there are ideas specific to this motor design I am quite interested. Of course I would not think placing this design directly on a wood stove would be ideal but I have been considering a few options to eliminate direct contact.

I have bumbled my way through some calculations, which I'm sure will have error. If anyone could please offer some input on how and what I may improve on it would be greatly appreciated.

I will counter sink the displacer cylinder 1/8" in to the top and bottom plate. Additionally I will allow for 1/4" on top and bottom for adjustment and so the displacer piston does not hit the plates.
I believe this will subtract 3/4" from my total usable travel of my displacer piston.
Measurements are in inches

overall displacer cylinder height-4.4
displacer cyl diameter-4.1
displacer cyl radius-2.05
displacer cyl circumference-12.874
total usable displacer cyl. height-3.65
displacer piston height-2.43"
displacer cylinder swept height-1.2"
total displacer cylinder volume-54.79
displacer cylinder swept volume-15.84

Hello? Any one out there?

Yes we’re still here, just slow. Your math is fine but doesn’t account for a displacer to chamber side clearance/air gap or some other form of passage/regenerator. That would lower the swept volume a bit. Some of the compromises are flow, heat exchange, regeneration, isolation, and dead space. Then make all of that work mechanically with minimal friction and maximum sealing and you’re good to go. Nothing to it. (In my case the design also needs to allow for a lack of obtainium, skill, and gumption.)

At any rate, while as much swept volume as possible is desirable, it’s the total internal volume, (not including the displacer,) that determines the actual displacement ratio of the power stroke. It looks like you will have around 25 cubic inches internal volume. If you have (for instance) a 1.25 cubic inch power stroke, that would give a 20/21 displacement ratio through the cycle. For numerous reasons most engines need about twice the temperature difference as the displacement difference, to have enough heat flow and pressure difference to run - in this example about a 20/22 temperature difference. That could be as low as a 200f bottom plate and a 140f top plate. It would need more temp. difference to make much power, but should be able to spin a fan. A bigger power displacement has a higher power potential at higher temps but wouldn’t start as well. Good luck, have fun.

Bumpkin

I just read the " lack of obtainium, skill, and gumption.", I'm going to feel right at home here!

johndilsaver
sparta, mo