Big Beta Stirling 1kw, 100degC to 400degC

[zhivko]

Hi Guys!

I made a test to see how power piston breathes as GeofV and Ante suggested. If I assume correct power piston should follows movement of displacer (of course with some lag) - it seems it moves for around 5-6 cm.

Test could be seen on following video:

manually testing powerpiston movement
or
link to video

Thanks for any comment....

[Geoff V]

Zhivko

Welcome back, hope you had a good Christmas break.

From your test results and with the new dimensions, I would expect the engine to run OK if the friction losses are low enough. Having the engine mounted with the cylinder horizontal will not help, as the displacer and piston mass will have to be supported against the cylinder wall. If you have time, it would be interesting to measure the friction as is (with the heater removed) and then with the cylinder in the vertical plane. Either way I'm sure it will run, the only unknown is how fast as this will dictate the power output, I'll stick my neck out and guess you'll see 1watt/rpm when mounted with the cylinder vertical.

Good luck.

GeoffV

[Ian S C]

zhivko, have a look for the low temperature Stirling Engine thesis from Canterbury University, New Zealand, I seem to remember tise was to design an engine of (I think) 1Kw, If I find the web site, I will post it here.
Building engines like this is a good way of spending the money you win on the lottery. Ian S C

[zhivko]

Happy new year to everyone!

Ian I think that you meant this link: canterbury LTD stirling.
I got a lot of useful info from this link. I especially liked the idea of heat exchangers that could be arbitrary sized is very well explained. Somehow thesis seems unfinished because of lack of time.
Such LTD could be easily used with vacuum solar collectors...

However I still need to finish my beta design first...

Thanks,
Klemen

[Ian S C]

Klemen, yes I did see that by the time the thesis required to be submitted, the practical work was incomplete, I have not been in contact with any of the Stirling Engine team over the last couple of years, so I don't know if it got finished, but I hope it did. If nothing else has been proved, the fact that you need a good bit of cash to build a working engine. There are a number of Universities around the world working on Stirling Engines, from USA, Japan, Italy, new Zealand, and I imagine some other places, as well as the comercial R&D. Ian S C

[zhivko]

FINALLY!

It works...

I still haven't measured the power but I see I have sealing problems between hot and cold cylinder - but stil I think it looks promissing.

Thanks anybody who helped me with ideas especially GeofV, Ian and Ante !!

Picture:

BigBetaStirlingRunning.jpg (52.76 KiB) Viewed 8551 times

Here is video:
Video of big beta stirling rolling

[derwood]

Good job! I think I can hear a leak. From the sound, it seems to be leaking quite a bit. Fix that and you will probably see quite a bit of power increase.

[NRG]

Happy new year to everyone!

Ian I think that you meant this link: canterbury LTD stirling.
I got a lot of useful info from this link. I especially liked the idea of heat exchangers that could be arbitrary sized is very well explained. Somehow thesis seems unfinished because of lack of time.
Such LTD could be easily used with vacuum solar collectors...

However I still need to finish my beta design first...

Thanks,
Klemen

Тhanks zhivko and Ian S C for the thesis hint. From the first looks, the ideas are very similar to mine. Congrats on your success as well!

[Geoff V]

Zhivko

Well done, clearly the fundamental proportions are OK, but that leak!

Perhaps the time is now right, to slow down a little and spend more time on carefull assembly.

GeoffV

[zhivko]

Yes! I should fix this leak - I should use O-ring instead of flat seal...

From the working success few days ago, and rethinking the situation from that time on, it seems that reason for bad efficiency is the lack of surface heat area (that is especially true in my case when engine is big).
So - I would humbly ask if somebody has some clever solution how to increase efficiency.

My idea is as follows:

Stirling2_1.jpg (151.15 KiB) Viewed 8495 times

Radiators in my case should be small tubes (diameter 6mm), that are placed in larger one. Botom one could be cooled by water and upper one would be heated by gas. Has anybody any better idea?

[Bumpkin]

zhivko, thanks for sharing your project. I've been following your build and if the goal is fun, it's already a success. As far as keeping the design simple and accessible, I don't know about the internal radiators, but I believe your expansion ratio might still be too high. I think your power stroke should be about half the distance the piston traveled freely when you moved the displacer by hand. Lower compression would be easier to seal too. To mention a point you've probably already thought of - whatever the output, it's conceivable that your engine could freewheel itself up to self-destructive and potentially dangerous speed - you might want to consider a governor. Bumpkin

[zhivko]

zhivko, thanks for sharing your project. I've been following your build and if the goal is fun, it's already a success. As far as keeping the design simple and accessible, I don't know about the internal radiators, but I believe your expansion ratio might still be too high. I think your power stroke should be about half the distance the piston traveled freely when you moved the displacer by hand. Lower compression would be easier to seal too. To mention a point you've probably already thought of - whatever the output, it's conceivable that your engine could freewheel itself up to self-destructive and potentially dangerous speed - you might want to consider a governor. Bumpkin

I did some rethinking and I assume that power stroke could stay as is - if I could just increase heating and cooling process.

If gas is more heated it would stretch more - thus allowing the power piston displacement stay same and give more power. Is this wrong thinking?

Heating and cooling 9 litres of air with small heat transfer area (in current working prototype I calculated around 0,2 m^2) is not viable.
If I use something like this heat exchanger I bet I should see improvement :)

[Geoff V]

Zhivko

Before you start cutting and changing the engine I would respectfully suggest you 'fix the Bloody leak' and see where you've got to so far and never mind worrying about the engine 'freewheeling to destruction', trying to pump 9ltrs through a 3.5mm wide gap will stop it overrevving for sure.

If you wish to do some calculations regarding 'how many tubes' it would take to flow 9ltrs, you will quite quickly realise the better route is much smaller swept volume and some pressurisation.

GeoffV

[Bumpkin]

zhivko, you already made clear that the leak is a priority, so it'd take quite a leap of doubt to assume you're not already pursuing a fix. I assume you'll do it. It'll be interesting to compare performance before and after: I think your engine shouldn't have more than about a few p.s.i. difference through a revolution. If it's too high, fixing the leak could actually hurt performance - or a lower compression ratio might help fix the leak. At any rate, if you add external exchangers the dead space will lower the compression and you might retest or recalculate expansion ratio then. Exchangers would open up the flow a bit and even a few hundred R.P.M. would be a lot of inertia… I've been looking at this engine as a wonderful novelty, but I just now noticed that you called it a prototype?
Bumpkin

[zhivko]

zhivko, you already made clear that the leak is a priority, so it'd take quite a leap of doubt to assume you're not already pursuing a fix. I assume you'll do it. It'll be interesting to compare performance before and after: I think your engine shouldn't have more than about a few p.s.i. difference through a revolution. If it's too high, fixing the leak could actually hurt performance - or a lower compression ratio might help fix the leak. At any rate, if you add external exchangers the dead space will lower the compression and you might retest or recalculate expansion ratio then. Exchangers would open up the flow a bit and even a few hundred R.P.M. would be a lot of inertia… I've been looking at this engine as a wonderful novelty, but I just now noticed that you called it a prototype?
Bumpkin

Bumpkin,

thanks for remark, Yes it's prototype, and i am already working on fixing the leak (would place oring instead of flat anular sealing). I would like to see it giving more power - and I know the power is the difference between input and output heat. So for the hot exchanger I had something like this in my mind:
296 stainless steel 6mm diameter, 1mm thick wall tubes in 1 meter long exchanger pack. That should give (if my calculation are right :) ) heating area of 3,7 m^2 - heated by same propane butane gas heater that you see on upper photos.
For cold exchanger I would use shorter exchanger - around 0,4m in length - it would be water cooled.
See half section view below:

HeaterAss.jpg (40.56 KiB) Viewed 8446 times

Oh yea And I am thinking about sealing displacer - could anybody suggest a sealing - it should adapt quite a lot to cylinder because tolerances are big, and shouldn't produce a lot of friction...