Solar LTD Displacer

[jman120193]

Hi,
I am currently building my first stirling engine as part of a school project, I have based my design aorund the solar LTD sold by kontax and scaled up the dimensions of these parts to create a larger engine.
However I am unsure on what to do when it comes to the displacer size and the stroke length. I have increased the diameter of both the displacer cylinder and the displacer, i have also increaed the height of the displacer cylinder, my problem comes with should I then increase the thickness of the displacer, keeping the stroke length the same; or keep the thickness the same and increase the stroke length?
Thanks in adavnce for any help, this may seem like a simple question but i have sort of thrown myself in the deep end with this project without really understanding all of it.
Many thanks,
Jordan

[Ian S C]

Hi Jordan, I imagine its the KS 90 vertion , I think if you just scale it up all over would be OK. You should keep the clearance top and bottom and at the side of the displacer as near as possible to the original motor. Ian S C

[jimlarsen]

Yes, scale up evenly. Do some math on the original to determine what percentage of the volume is consumed by the displacer in the original, and then make yours a similar percentage. On my LTD engines the displacer is usually 1/4 to 1/3 of the internal volume. However, that is not a critical calculation. The swept volume is more important. That is determined by the area of one side of the displacer multiplied by the length of the stroke. There is a ratio of swept volume/total volume that you want to keep about the same.

The swept volume and the temperature differential will also determine the displacement requirements of your drive mechanism.

As you increase the length of displacer travel it means you are lifting farther with the crank and flywheel. It also means an increased angle between the displacer and the crank when lifting. If you add too much you eventually reach a point where the increase in friction and load outweigh any benefit for additional swept volume.

If you scale up so that the ratios are close to being the same, you probably won't have much trouble.