Imploding displacer - make it leaky?

Discussion on Stirling or "hot air" engines (all types)
tom-rock
Posts: 16
Joined: Tue Feb 25, 2014 1:24 pm

Imploding displacer - make it leaky?

Postby tom-rock » Wed Nov 01, 2017 1:03 pm

Hi all,

yesterday my displacer imploded and it was my second one recently.

Now I ask myself if the next one should be more sturdy (which makes it heavier and more heat conducting what I want to avoid!)
or if there is a way to make a pressure compensation without creating additional dead space.

I think about a very small ´vent hole´ or a special kind of valve.

Mean pressure is 10 bar (145 psi) and max workingpressure is approximately 15 bar (217 psi).

If someone has some experience with this problem or has an idea for pressure compensation I would be very thankful
for an answer.

To get an impression of it and a picture of the destroyed displacer you can see it in this small video:

https://youtu.be/VcULP9Y-01A

In an older video a few month before you can see the other imploded displacer.

It really gives you an impression of 250 watts power when the engine stops immediatly from 2000 rpm.

Greetings

Ralf

Ian S C
Posts: 1983
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Imploding displacer - make it leaky?

Postby Ian S C » Thu Nov 02, 2017 3:00 am

What is the displacer made of? No you don't want any sized hole in the displacer inside the motor, with an atmospheric motor I have used a hollow guide rod venting the displacer to atmospheric pressure.
This is the result of using aluminium for a displacer, the third displacer was made of stainless steel about .25 mm thick, its still going strong. Once aluminium gets up to 300*C or more(quite easy to do) it loses its strength, much more and it would melt.
Ian S C

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tom-rock
Posts: 16
Joined: Tue Feb 25, 2014 1:24 pm

Re: Imploding displacer - make it leaky?

Postby tom-rock » Sun Nov 05, 2017 1:10 pm

Hi Ian,
the displacer is made out of titanium which also looses much of its strenght at high temperatures as I read now.
Maybe I will try a good titanium alloy or stainless steel if the new one (also out of pure titanium but a bit more sturdy and with 2 instead of 1 radiation shield) which in nearly ready will implode also.
The idea with the hollow guide rod is ingenious !
The displacer will have mean pressure without any leakage to the working space.
Maybe the displacer rod needs a bigger diameter to bore it but I will think about this seriously!
Many thanks for this nice idea.

Greetings

Ralf

Ian S C
Posts: 1983
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Imploding displacer - make it leaky?

Postby Ian S C » Sun Nov 05, 2017 6:40 pm

The engine that has made the most use of the hollow rod hasa a bore of 1 3/3", and the rod is made of 5 mm stainless steel tube, its disassembled at the moment, but in its life since 1994 it has probably put in over 2000 hours of use. the busf through the piston is made of Teflon and that shows no sign of wear, but the rod has a little, the motor is horrizontal so all the weight is on the bush. the displacer on that motor is made of mild steel.
Ian S C


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