Stirling Engine PE2

by dougconner, published

Stirling Engine PE2 by dougconner Nov 16, 2012

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This is a Stirling engine which is a type of heat engine. It needs about a 50 degF (28 degC) heat differential to run and cruises about 300 rpm unloaded.

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Wow! Great engineering Doug.

i'm printing one right now, but it feels so light. what's the infill ? and is it different for each part ?

Saw one of these in operation over an incadescent lamp at the Inside 3D Printing Conference in San Jose last week.

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All the plans and information to build this engine is now available. You can see lots of information about the engine with a video of it running at solarheatengines.com/2012/10/29/3d-printed-stirling-engine/

The zip file contains all 11 3D printed parts for the engine.
PDFs provide assembly drawings and parts drawings. A discussion of building these parts is available at solarheatengines.com/2012/11/21/3d-printed-stirling-engine-now-open-source/

An assembly and BOM PDF is now available. More assembly details are available at solarheatengines.com/2012/11/27/3d-printed-engine-bom-and-assembly-instructions/

I've posted an article on building the regenerator for the PE2 engine. If you build the engine you want to be sure to build one for good performance. I've included information for those wanting to learn more about Stirling engine regenerators too. solarheatengines.com/2012/12/18/a-regenerator-for-the-3d-printed-pe-2-stirling-engine/

I've posted an article on alternate designs for the power piston and the displacer. These new designs will not affect the engine performance, but may be simpler to build. The STL files are available in piston insert 3.zip and displacer3.zip. The article is at: solarheatengines.com/2012/12/31/new-power-piston-and-displacer-for-3d-printed-stirling-engine/

To build this engine you need a drill press to accurately drill out the rough 3D printed holes and for drilling the aluminum plates. Some simple lathe work is necessary to machine the power piston to fit in the brass tube.


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theevilorverlord on Feb 3, 2014 said:

Wow! Great engineering Doug.

Nazif on Oct 7, 2013 said:

i'm printing one right now, but it feels so light. what's the infill ? and is it different for each part ?

ForrestHiggs on Sep 23, 2013 said:

Saw one of these in operation over an incadescent lamp at the Inside 3D Printing Conference in San Jose last week.

dougconner on Dec 19, 2012 said:

It looks like good printing resolution. I'm concerned the temperature limits might be lower than ABS. Definitely something to watch.

idolcrasher on Dec 6, 2012 said:

really fantastic :)

exergy123 on Dec 2, 2012 said:

Great!! Thank you very much!!

thatguy6669 on Nov 29, 2012 said:

If using slic3r scale by 2540% and the model will print at the correct dimensions.
1 in = 25.4 mm  

dougconner on Nov 29, 2012 said:

 Thanks, this will be helpful for people with that software.

3DTOPO on Nov 19, 2012 said:

With 120F temperature delta, how large do you think this would have to be to generate 1kw? I have a 155F hot spring, and a cold creek. I would love to be able to generate some juice from it. I have about 220kw of heat potential, so even with a very low Carnot efficiency I should be able to get some usable electricity. Do you know what the Carnot of this engine is with 120F delta?

dougconner on Nov 19, 2012 said:

The answer to your question is you could probably make a 1kw engine using your hot and cold water sources--but it would be a big project. The Carnot limit for 155F and 35F is 20%, but it would be a real engineering triumph to make a system around 5%. If I was trying to build such a system I would hope to get 5% but anticipate around 2-3%. 

To give you an idea of the magnitude of the project, take a look at this article and video of a 1kw low-temperature differential Stirling engine. http://www.solarheatengines.co.... 
It uses a higher temperature ratio but is similar. 

With your source of hot and cold water efficiency wouldn't be as big of an issue (2% would work). I can tell you that there are other people that would be interested in such an engine if it was reliable and could pay for itself in a few years of operations.

Organic Rankine cycle turbine engines are are also used for generating power at your temperature levels. 

jag on Nov 18, 2012 said:

Is there a reason you used the foam with the displacer instead of just printing the whole thing?  Seems like you could print it with very low infill and have it be just as light.

dougconner on Nov 18, 2012 said:

I'd like to be able to print the displacer in one piece but I was not sure that I could make it both light and air-tight. For the displacer to work properly it cannot let air leak in or out of it except over long periods (tens of seconds or minutes). The large flat surfaces must also not flex when they are subjected to the +/- 0.5 psi pressure variations during operation. 

The other reason for using foam is that I have another version of the engine (all the printed parts are identical) but with more aluminum plates for internal heat transfer. This other version uses a displacer that is only 0.5 inches long instead of 1.0 inches. All I have to do is remove two of the foam plates. 

I don't have a 3D printer yet, but I'm hoping to get one soon. My engine was printed by Stratasys. This engine was my first 3D printed design. I knew very little about 3D printing and made what I felt was a conservative design that would work on the first pass. I'm still amazed it did. I'm also hooked on 3D printing. 

I have several parts on the engine I'd like to improve to simplify building the engine. I'm concerned about getting a 3D printer that can make accurate ABS parts. At the moment I can't really justify buying a Stratasys printer for $10K, but I could probably spend around $2K. My question is which one and will I be satisfied with the results? For example, Stratasys doesn't have a problem with overhangs, but as I understand it, many of the lower-end printers do. I also measured no detectable warping and the accuracy was excellent. 

maxumx on Nov 17, 2012 said:

looks like a good LTD sterling. make me wonder if a thermoacoustic type could be made in a simmiler way.

dougconner on Nov 17, 2012 said:

Interesting idea. I've never seen a LTD thermoacoustic engine. All the ones I've seen take a pretty hot flame. If you know of any LTD thermoacoustic engines, send me a link. 

chaleg on Nov 16, 2012 said:

The STL files come in very small. What did you scale them as to print your model?

dougconner on Nov 16, 2012 said:

I designed this engine in inches. The hole for the displacer in the cylinder body should be 3.00 inches in diameter. Is that the problem?

chaleg on Nov 16, 2012 said:

I am a retired Australian engineer and am always looking for interesting projects. I will start to print the parts later today. 

mkeveney on Nov 16, 2012 said:

Cool.  There's an animation explaining how this engine works here:

(forgive the shameless plug!).