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Since the steel wool displacer isbsupposed to do two jobs 1. Displace. 2. Store and release heat.
Has anyone tried aluminum wool instead of Ssteel or steel wool?

I t would depend on what temperature you are going to run the motor first off. But for the same reason that it is best not to use aluminium for any of the hot end, no don't use it. The most important reason is that aluminium conducts heat too fast, the idea is to keep the hot at the hot end, and the cold at the cold end. With stainless steel, the heat is dropped off as it transfers to the cold end, and is picked up as it comes back. An ordinary cylindrical steel/stainless steel displacer of the correct length to diameter also does this. In my adventures with displacers I have had the most success with plain cylindrical stainless steel, or steel. Very little success with stainless wool. Three melt downs with aluminium cylinder displacers, all on one motor (slow learner)
Ian S C

Ian SC
Thanks for setting me straight. So following your explaination would it be better to just have the regenerative steel wool on just the hot end of the displacer instead of the whole length?
And if using a hollow steel displacer, would a pin hole be advised to equalize the pressure inside the displacer, like on the NASA free piston Stirling?

If you follow my example, forget steel wool. On a displacer moving at up to 1500rpm or so, and being heated, maybe to near red, the wool breaks down and starts to move around in the engine, with the chance of getting in with the power piston and damaging the bore.
With a hollow steel displacer no hole should be allowed into the displacer chamber, but you can use a hollow displacer rod, it doesn't seem to matter if the interior is vented to atmosphere. the pressure is very small, although enough to collapse an over heated aluminium one.
Ian S C
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