Hi,
I've been working on some Stirling Engine designs and it crossed my mind that the term "displacer" may be a misnomer.
That is, in your typical Stirling Engine, I don't believe that the bulk of the displacer actually serves any purpose.
It seems to me that the so-called displacer simply directs a stream of air one way or the other creating turbulence and that a relatively thin plate or even a diaphragm would serve this purpose just as well.
Here is an illustration of what I mean.
http://prc_projects.tripod.com/inturb.html
In the second (smaller image) some groves have been cut into the side of the "displacer" to create more turbulence (theoretically) that is a circular cyclone type motion. This could also be holes drilled through the "displacer" at an angle, or vanes set at an angle.
I was also considering calling this type of displacer something like an "inturbulator" as its function is not actually to displace the air but to enturbulate it, driving it against one side or the other of the chamber (hot end or cold end).
I don't have the equipment here to build and test this but I thought someone else might be able to try it and see if the theory is correct.
[url]http://prc_projects.tripod.com/inturb.html[/url]