Stirlingengineforum.com

Hello everyone,

I'm wanting to design and build a gamma type stirling engine to run small machinery such as a small water pump, metal lathe, tiny drill press, etc. In other words an engine with an output of around 200 W or 1/4th HP. If this topic has been covered already, a link to it would be great.

In looking through books written by Andy Ross, Martini, and James Rizzo, I see there are many techniques and ways to go about designing such an engine. At the moment it seems like I have a bunch of "dots" that are not connected with any "lines". What I need is some guidance on what direction to go. So far, this is what I'm thinking of doing:

1) Decide on engine layout such as vertical or horizontal displacer, possible linkage, etc.

2) Use the normal rules of thumb to get initial sizes for cylinder diameters, piston/displacer stroke, etc.

3) Use the Schmit Cycle (spelling?) equation to calculate the needed heat input and output. (It seems this is VERY dependent on engine RPM which I don't know how to predict.)

4) Design the hot end, cold end and regenerator to add/remove the needed heat, taking into account the various heat looses and short circuits.

5) Engine final design, including working drawings.

6) Assemble engine and begin trouble shooting to find out why power output is nowhere near the design.

Am I anywhere close to a good design scheme?



Sage Brush

Sage Brush, have you built an engine?, a small one roughly along the lines you are thinking about would be a good idea to get you started. Even a small /mini lathe is enough to bore the power cylinder, and make a fitting piston, and make the crankshaft.
Ian S C

Hi Ian S C,

No, I haven't built an engine before. Since I spent over five years working as a machinist and have access to a lathe and mill, I'm hoping this won't be beyond my skill level. But It sounds like you are saying an engine this size could be harder than I think. I've been getting into Mechanical Engineering as a very serious hobby, hence my asking about designing an engine from scratch. I guess I should clarify and say I'm REALLY interested in analyzing the design so I can roughly predict the performance before I go to the trouble of building something.

The other approach I thought about was finding an engine with similar specs and tweaking it for my purposes. For instance, I noticed the engine mentioned here:http://www.stirlingengineforum.com/view ... 1904#p2198
The engine I was thinking of designing would be something similar. The power output is supposed to be 1/8 HP or about 96 W. I figured if that was truly the output, then I might be able to double it by putting finns inside the hot and cold side, adding a water jacket, adding a regenerator, etc. Hmm, I really need plans for an engine that at least has an output of 200 W to have any confidence.

Sage Brush

[youtube]https://youtu.be/v_e0981CLDI[/youtube]

Hi, not sure how to fabricate it but it says 500 Watts.

[youtube]https://youtu.be/HqdoCzNAzHM[/youtube]

[youtube]https://youtu.be/rGFiaL_gYhU[/youtube]

Hi, I found another project, looks like it has nice torque.

[youtube]https://youtu.be/jl9tw6Ysb4s[/youtube]

Big gamma, using a small tire as a diaphragm.

great

[youtube]https://youtu.be/9jQgAnPrwbM[/youtube]

https://www.nmri.go.jp/eng/khirata/stir ... strct.html

300 watts Gamma

http://www.starspin.com/stirlings/jimd2.html

150 watt project with specs

Hello Everyone,

Thanks for all the replies. Its been a long time since my last post. I have been busy reading the book, Stirling Cycle Engines by Allan J Organ.
The book has helped me somewhat and confused me somewhat. Here are some things from the book I thought interesting:

1) Most research understandably has gone into high pressure hydrogen filled engines, not air filled low pressure ones, so there may not be much info to go by for design

2) Gas flow inside a Stirling Engine is VERY complicated (unsteady, compressible flow)

3) The Schmidt Analysis should not be used for a Stirling Engine because it assumes and oversimplifies the processes taking place the engine

4) For most engines using air at atmospheric pressure, 1/2 watt per cc of power piston swept volume is typical

5) To see if a given design for an atmospheric pressure engine is crazy or not, one can use the Beale Number provided some corrections are used (I'd explain but haven't tried this yet)

6) The book's chapters on scaling (FlexiScale and ReScale) might be useful if I make/find an engine that I want to duplicate in a different size

7) Chapter 15 gives a possible method for calculating heat exchanger size and shape (number of finns or slots)

8) The author makes it clear that the phase angle (in my case power piston vs. displacer) may not be optimal at 90 deg. and gives ways of calculating what the angle should be

9) The ratio of swept volumes (power piston swept volume to displacer swept volume) may not be optimal at the usual 1:1.5, again the book lists ways of figuring what the ratio should be

10) Dead volume is not always a bad thing, the author talks about an engine that would not run until the dead volume was increased, though I'm not clear on how to tell when more dead volume is ok

11) Chapter 20 has a nice way of calculating the heat that needs to be transferred into the engine for a given efficiency and wanted power output which will come in very handy


To sum up, the book does not spell out the steps to take but does have good things to say.
Still, I feel like I barely understand how to go about designing an engine and need to do more reading.

@burnit0017, I haven't looked at the link in your last post but the engine looks like the same style I'd like to build.

Sage Brush

https://www.youtube.com/user/approtechie/videos

[youtube]https://youtu.be/rGFiaL_gYhU[/youtube]

[youtube]https://youtu.be/HqdoCzNAzHM[/youtube]

Hi, I am newbe and I am just trying to duplicate the above project. Thanks for posting the info and I look forward toward results.

https://youtu.be/lsysqpVoDak

100 watts

[youtube]https://youtu.be/4lDMZ5SK-9A[/youtube]

http://peterlynnhimself.com/LSM_14.php

Sage Brush wrote:Hello everyone,
I'm wanting to design and build a gamma type stirling engine...........
Sage Brush

I think you will find everyone else is also trying to connect all the dots and that there does not seem to be anything close to a complete A-Z how to build guide on the internet regarding large powerful stirling engines or hot air engines. That said I have not read any of the books on amazon so perhaps you will have more success there. follow the force. May the force be with you.
Wellington