# Tamera video of Sunvention SunPulse engine

I came across this video of an interesting large, low-temperature Stirling engine. You’ll need to get to about 1:30 before it gets interesting.

The following numbers are based on what I have seen in the above video or statements the speaker has made and in a few cases, guesses based on what I can see. All my dimensional estimates are strictly eyeball and may easily be off by 20% or even more.

Sunpulse Stirling engine generating electric power

power piston diameter: est. 48 inches
power piston stroke: est. 2.5 inches
displacer diameter: est. 48 inches
displacer stroke: variable, est. 2.5 to 6 inches
flywheel diameter: est. 72 inches
flywheel rim: est. 0.5 inches thick by 4 inches wide
Operating RPM: est. 60 to 90
Heating and cooling pumps: est. 2 inch diameter by 3 inch stroke, double-acting
2×9.4 cubic inches per cycle = 312 grams (for water)
Operating temperatures: Hot oil or water at 5 bar pressure, 150 to 200 deg C. Water cooling, est 25 degC or higher

Estimate operating gas temperature Th=180 deg C, Tc=40 degC
Power output of generator: 1.5 kW
Engine pressure variation: +/- 0.1 bar (approximate in video of gauge)
Hot oil with possibly gravel stored in elevated barrel est. 55 gal barrel

Stirling engine driving water pump

flywheel diameter: est. 48 inches
flywheel rim: est. 2.0 inch diameter steel
displacer stroke: est. 5 inches
claimed pumping output:
(110,000 gal/day or 9200 gph for 12 hr day)
(22,000 gal/day or 1800 gph for 12 hour day)
(4100 gal/day or 340 gph for 12 hour day)

total solar collection diameter est. 11 feet including mirrors

There are several interesting features of this engine that I’ve tried to capture in these stills taken from the video. First, the robust power piston with what I would describe as a conical truss. If you want to get significant power out of a low-temperature Stirling engine, you need a big power piston. I estimate the power piston at 48 inches in diameter. combine that with a pressure fluctuation of about 0.1 bar (1.5 psi) shown on the gauge in the video and you have a peak piston force of around 2700 lbs.

An atmospheric Stirling engine such as this will have an approximately sinusoidal pressure versus time with two power peaks per revolution. One half the cycle will be above atmospheric pressure and one half will be below atmospheric pressure . The average force =.64 x peak force or about 1730 lbs. I estimate the power piston stroke at 2.5 inches so for a complete cycle the travel is 5 inches for a total of 8650 in-lbs of work or 721 ft-lbs per cycle. At 60 RPM this would be about 980 watts. This gets you in the ballpark of 1500 watts. At rated power this engine might be turning 90 rpm, the pressure might be even higher, or my power piston diameter and stroke estimates could be way off.

To me the most interesting feature of this engine was the variable-stroke displacer. The following photo labels some of the components. A motor-driven jack screw (which you can see operating in the video) adjusts a connecting rod anchor point on the lower displacer lever. When the connecting rod is close to the pivot the piston travel is long and when it is farther away the travel is shorter.

The reason you want to do this is to be able to quickly regulate the power output of the engine to match the load. The time constant for heating or cooling the engine might be minutes, but you need to adapt to electrical load changes much faster. This mechanism lets you operate the engine at a fixed temperature and be able to vary the displacer stroke to control the RPM. Closed-loop RPM control using this method is much better and less wasteful than say adding or dropping a dummy load to flat-load the engine.

The above photo also shows what I refer to as a rolling fabric seal around the circumference of the power piston that provides an airtight seal to the cylinder. The seal is probably a coated fabric that is flexible but does not stretch under the 1.5 psi operating pressure.

This last photo shows the engine-driven piston pumps that pump both the hot oil or water through the hot end of the engine and the cooling pump. Both of these pumps appear to be double-acting so they pump liquid twice per complete cycle.

This is quite an impressive project. Also see some information at Sunvention.

1. Ed Golla says:

Thanks for the info and analysis.
The variable displacer stroke is interesting.
It could allow tuning for different TH and TC.

The sunvention site states that the cylinder for the electric generator is 2m by 0.5m.
This is almost double your estimate.

The Sunvention site does state the cylinder for the electric generating engine is 2m x 0.5m, but it isn’t clear what that dimension is for. Is it the outside of the displacer housing (which is how I interpreted it) or the actual cylinder bore (which is how I think you are interpreting it)? After carefully comparing it with the flywheel diameter and the person in the video (only an eyeball comparison) I decided on the 48 inch bore. If I increase the power piston bore estimate to 60 inches, then my power estimate comes out close to 1500W.

3. Nick Raaum says:

Very interesting and informative website!! I stumbled across it in my search for more info on the sunpulse engine, which seems highly intriguing.

High volume low speed and short stroke seems like the right combo for acceptable efficiency at low temps. Plus the features like a fabric seal should help keep build costs down compared to conventional cylinder sealing techniques.

I wonder though if such an engine could be built to run without a crank and flywheel, and instead use a hydraulic free piston configuration? Any thoughts?

It should be possible, at least in theory, to redesign the Tamera SunPulse engine as a free piston engine. The large force of the power piston and the low frequency would make for a rather large moving mass and spring constant. Extracting the power might prove difficult too. One might try to use some of the techniques used in generators that operate from ocean waves. I only have a little experience with free piston engines so I am no authority.

5. Nick Raaum says:

Yes the forces are not trivial at this scale, my thought was that if a free piston hydraulic build were possible then scaling it down might make for a more cost effective solution (easier to build components). Perhaps around 150W output, similar to PV panels in both size and output. Then couple together hydraulically to scale as needed.

I’m tempted to take a crack at building a small scale gamma style free piston engine with a polystyrene displacer piston and a silicon tubing sleeved power piston to test this guess, though being a rookie I’m probably way out of my league….Will look at wave generators too.

On a non related note have you played around with the opposite direction of the stirling cycle (cooling). Seems like low cost DIY refrigerators are an interesting potential?

It should be possible to scale down the SunPulse engine. A gamma configuration should be easier design and build than a free piston.

I have played with Stirling engines as heat pumps. They do work. I have not measured efficiencies. One nice features of working on heat pumps for refrigeration is that you don’t need work with such high temperatures. This makes it possible to use plastics where their low thermal conductivity is an advantage.

7. Asif says:

Is it possible to collaborate among this enthusiastic group to build a scaled model of this sunpulse engine?

Anybody interested please voice up! I’m willing to shell out material cost if I have design help.

8. Nick Raaum says:

Asif,
Yes I for one am very interested in collaborating on a build of a sunpulse like engine. I’ve been trying to accumulate enough info on it to begin to evaluate its costs and potentials but have found very little. Without that a full out build may be jumping the gun (should that type of design have proved to be costly or ineffective ect).

Unfortunately I’m a bit new to stirling engines and have not yet built one but am quite interested in attempting something soon. I’d also be very curious though to hear what the owner of this site thinks of the idea of imitating the sunpulse. Do feel free to email me at raaumn at hotmail dot com if you want to talk more.

9. Greg says:

I would also be interested in collaborating on a scaled build of a low temperature solar stirling along the lines of the sunpulse.

I might be interested in collaborating on a low-temperature Stirling engine. Let me know what your specific goals are so that I can see if I think they are achievable. We can discuss this in separate emails.

11. Frans says:

Hi Frans here, did you guys ever build a model of the Sunpulse as I have 1/2 way built a small app 200mm dia version but am a bit stuck on the regen mechanism.
Cheers Frans

Unfortunately I have never seen any information on the inner workings of the Sunpulse engine. My guess would be that the regenerator is something similar to what I’ve done on the 3D printed Stirling engine regenerator. Instead of the nearly continuous circle of flattened tubes you could use perhaps 4 round tubes if that is more convenient. Another approach would be to use all or part of the displacer as a regenerator as I did here.

13. MikeW says:

Hi Doug, just sent you a couple of .pdfs I found on the internet about the sunpulse engine ages ago. Great to see other people are interested. I still hold that a Revetec based cam shaft design built out of UHMW or some other material would be a great way to go.

Great to see other people are interested.

14. franscubitt says:

Hi Guys,
Thanks very much for the feedback, MikeW could I ask you please to forward the pdf’s to me as well
I am busy with a +- 20% model of my proposed Oil Drum Striling to see what power doifference I get with or without a Regen and using a diaphram piston, I have built 4 different Stirlings, all models and 1 of the 4 just refused to work!! thats why befoore I go to a lot of work on the Oil barell I want to test out a model.
so far I havent used a regen in any of my models so need to experiment with one.
My aim is to try to build a low tech engine bulidable by poorer communitys for water, power of refrigeration
although it seems the only people raring to try are the people in India.
I would applreciate any help from people who have also made lager atmospheric Stirling engines.
cheers Frans
Cheers Frans

Thanks for the material. I can’t redistribute the material, as that would be a copyright violation. If you found the material available on the internet you can send the URLs and I could post those.

I take copyright violations seriously. I’ve had people steal my design PDFs, remove my name and website reference, and then sell the on the web.

16. MikeW says:

As far as respecting copyright, I can appreciate that posting something without giving due credit would be bad. I never double-checked the permissions for the doc’s when I found them or stored the historic URL. I believe they were released to public according to copyright notice. I did a search on the titles, here are some current links. Enjoy!

http://www.engr.colostate.edu/~marchese/mech337-10/epri.pdf
appendix pages 13-14

presentation near the end

Revetec – better matching between power piston and displacer – plus higher torque at pressure maximum. However, this is patented technology – I am not sure what that means for hobbyists
https://www.waset.org/journals/waset/v52/v52-77.pdf
http://www.revetec.com/technology.htm

Thanks Mike, that’s the proper way to share the information. If any of those sites are violating the copyright, they’ll get a take down notice and the problem will get fixed at the source. They also get credit for putting the material up.

18. franscubitt says:

Hi Mike
Thanks very much,
From what I have red so far super interesting info, I didnt know much about the Revtec engine but its fascinating as well.
Most appreciated
I have written to the folkes at Tamara asking if I may buy engine, kit, or plans as I am quite
happy to help pay for their research, “Time taken is Time given” in my book.
Cheers Frans

19. Asif says:

So I continue to see interest in this regard for various people. I suggested collaboration and people seemed to like it but no real progress. I’m willing to stick out my neck if the people here really want to help out in the design work. I live at Portland Oregon USA. I have collected quite some data and I have drawn a few section of the engine in autocad which I’m willing to share with a like minded researcher.
What the next step exchange email and open up a common Google docs work space? the goal here is to recreate the Sunpulse engine at USA!