Stirling Engine displacer

[Ken Ratcliffe]

I have just about finished a Jonkman Stirling Engine (first engine after a series of clocks), but can't think how to make the brass displacer, other than from a solid a brass rod, but I am not sure that is the best/right way, nor that my lathe skills will stretch to it. Any help much welcomed.

 

[tornitore45]

Have no idea of the Jonkman Stirling Engine but usually Stirling engine displacer are as light as they can be. Aluminum tube with glued ends. Tinplate wound on a broomstick, lap soldered and soldered ends. The trick is to have a sufficiently deep and rigid boss to keep the rod on axis so that the displacer run without dragging in its tube. People have used all sort of available cylindrical containers.

 

[Ken Ratcliffe]

Hi Mauro......it makes sense that it needs to be light, maybe to be in keeping with the rest of the model I could use brass shim stock (these are the plans - http://www.plans-for-everything.com/downloads/stirling_engines/ST Jonkman.pdf if you are interested)

 

[deverett]

Aluminium is not the best material for a displacer because of rapid heat transfer. Stainless steel is a much better option, even mild steel can be used.

What Tornitore45 suggests is good, but make sure you use hard silver solder (55% or similar) for your joints.

Dave
The Emerald Isle

 

[Technical Ted]

I just made one of these and posted about it a week ago. I cut my displacer out of solid brass 360 bar stock. About 0.015" wall. I cut the internal radius with a radius end mill in my lathe. After hollowing it out and cutting it off, I made a steel piece with the same radius and a sliding fit on the OD to fit inside it. I used this to support it while machining the outside to size and the external radius on the end.

Ted

 

[Technical Ted]

Here's a video of the one I just made. The displacer must be light in weight or I think you will get too much fiction.



Ted

 

[Longboy]

Most convenient way is a brass or aluminum tube, Pyrex test tube or graphite round drilled out. End cap plugs of flanged aluminum epoxied in with a groove machined in to hold some of the adhesive. For test tubes, a flanged plug grooved for a pair of O-rings to grip the inside of the glass or graphite displacer works well. It does not matter the tube material on its heat retention capacity nor the weight. Your engine will run fine at double the gram weight of its displacer you are using, more so in a horizontal position.
http://www.ksmetals.com/26.html

 

[minh-thanh]

Most convenient way is a brass or aluminum tube, Pyrex test tube or graphite round drilled out. End cap plugs of flanged aluminum epoxied in with a groove machined in to hold some of the adhesive. For test tubes, a flanged plug grooved for a pair of O-rings to grip the inside of the glass or graphite displacer works well. It does not matter the tube material on its heat retention capacity nor the weight. Your engine will run fine at double the gram weight of its displacer you are using, more so in a horizontal position.

I often use aluminum for displacer on my engine .

 

[Stefan Jüngst]

I´ve thought that the function of a displacer in a Gamma or Beta-Stirling is to buffer most of the heat and give it back later. So Aluminium would be exactly the best choice because it´s light weighted and have a real good heat-transfer. Or am I wrong??
By the way - an wonderful piece of art, Ken.

 

[Technical Ted]

I'm not totally up to speed on the design principals of Stirling engines so I can't answer your question. I followed Jonkman's design and he stated brass. Also, IMO, brass looks best in this design. I've made three of these now and they are show pieces. They run very nicely, but they are just beautiful to look at! They spend a lot more time being looked at then they do running...

Ted

 

[Stefan Jüngst]

you are really ressourceful ... building Stirlings without knowing fully the principles - I wish I would have ur skills and chuzpe to do the same ... I´m a damn rooky and learning everything by myself. Build only 2 Stirlings and a thermoacoustic one, which is not really working ) Wish u the best Stefan from Holstein/ Germany

p.S. the first "working engine" you´ve build, you will never forget, do you??

 

[tornitore45]

The function of the displacer is to... displace air. Is the fundamental principle of a Stirling to move the working fluid in and out of the power cylinder.
Buffer or Store the heat is the function of the Accumulator, the steel wool stuff in the middle of the air path. As the word imply the accumulator acts as an electrical accumulator (aka battery) heat is loaded into the materiel mass and released. The reason is made of steel wool or similar structure is to expose the most area for a given mass.

 

[Technical Ted]

you are really ressourceful ... building Stirlings without knowing fully the principles - I wish I would have ur skills and chuzpe to do the same ... I´m a damn rooky and learning everything by myself. Build only 2 Stirlings and a thermoacoustic one, which is not really working ) Wish u the best Stefan from Holstein/ Germany

p.S. the first "working engine" you´ve build, you will never forget, do you??

Hahaha, yeah, I'm resourceful. I downloaded the complete and excellent drawings that Jonkman made and provided (for free)! They are readily available on line and free of charge.

I followed them exactly except for slight modifications because the test tube I found was a little different than his specified diameter. He's the smart one!

Ted

 

[fcheslop]

When I made my Stirling 60 the displacer was from aluminium and its never been a problem
To make the internal rad I just ground a twist drill to a near enough guess to the required rad then glued it onto a mandrel to finish the outside
For this wee engine I doubt a re-generator would be of any benefit. Although Iv just made one for the 2inch bore Ericsson engine and it now runs on one 5/16 dia wick meths fired before it needed two and clips along fast enough to need the regulator opening to slow it down
cheers

 

[Stefan Jüngst]

The function of the displacer is to... displace air. Is the fundamental principle of a Stirling to move the working fluid in and out of the power cylinder.
Buffer or Store the heat is the function of the Accumulator, the steel wool stuff in the middle of the air path. As the word imply the accumulator acts as an electrical accumulator (aka battery) heat is loaded into the materiel mass and released. The reason is made of steel wool or similar structure is to expose the most area for a given mass.

Hi there, yes I´m familiar with the concept of the Accumulator. But the "regenerator" is only used for the Alpha-Type style stirlings. I´ve never saw a Beta- or Gamma-Type with an extra accumulator. What I`ve read so far, it´s because the great surface of the displacer is functioning as good as an extra accumulator. But I´ve got so many times surprised.
So - if you have examples for Beta or Gamma Stirling with an extra regenerator, I would be very thankful, if u can post it.
Many thanks.

 

[Mechanicboy]

But the "regenerator" is only used for the Alpha-Type style stirlings. I´ve never saw a Beta- or Gamma-Type with an extra accumulator.
Many thanks.

All stirling engines Alpha, *Beta and Gamma type has "E" regenerator.. see this picture.

 

[Stefan Jüngst]

All stirling engines Alpha, *Beta and Gamma type has "E" regenerator.. see this picture.

View attachment 111611

Thanks for the pictures - I think I´ve only seen pictures and animations of low-level toy-stirlings so far. Did you see a real Gamma or Beta Stirling with a regenerator?? I never did - also not in the Stirling-Convention in London 4 years ago. Must be unpractical and too much work for such toy-stirlings.
P.S.
I searched in our forum and found a Gamma-Robinson Stirling with an integrated regenerator in the displacer, very nice work : https://www.homemodelenginemachinis...r-engine-that-will-not-run.23222/#post-250269

 

[Ken I]

Ted,
Thanks for the post - I'm in the middle of building one - about half the parts done.

Nice to see one running - its a nice running bar ornament - the reason I chose it.

How did you cut the test tubes - I bought 5 - I hope to break not more than 4 .

Ken

 

[Mechanicboy]

I created the Alpha stirling engine with regenerator in may 1996 (2 power piston), the engine had 20 mm stroke and 35 mm bore. The regenerator was made of copper wire packed in the room for regenerator. There was 10 thin 3-4 mm copper pipe between cylinder in cold side and regenerator in cooling water and the other side of regenerator connected direct to the cylinder in hot side. The engine ran 1000 rpm with cooling water in around 80 degree in normal working temperature. All was ball beared. The phase angle was set to 120 degree instead 90 degree since it was impossible to start up the engine with high compression due heat input was not enough. The engine got more heat input by the big phase angle and was able to start it easily. The pistons of mild steel was sealed with well oiled leather disc in bottom of the pistons on the polished cylinders of pipe from vacuum cleaner, friction was not problem. Both cylinders was in the cooling water jacket while the part of hot side sylinder was outside the cooling jacket while the leather discs was cooled under running.

 

[fcheslop]

Also dont forget about invisible regenerators as in the leading edge of the displacer does have an effect on air flow
One of Robert Stirlings early engines had a regenerator
https://www.stirlingengine.com/regenerators/#3
cheers