Stirlingengineforum.com

airpower wrote: ↑Tue Nov 16, 2021 1:55 am Ross yoke linkage machines operate on 120° thermodynamic angle instead of the conventional 90°

That might explain the problem. That engine seemed to be struggling very hard. The Ross yoke may not be a good choice for this engine.

Tom Booth wrote: ↑Tue Nov 16, 2021 2:21 am

airpower wrote: ↑Tue Nov 16, 2021 1:55 am ...
No matter what all require at least 35° Fahrenheit (1.67°C) temperature difference to operate.

Your conversion is not correct.

A 1.67°C ∆T translates to about 3 or 3.5°F (or is that 35 a typo? Missing decimal point?)

According to Senft, some LTD engines were able to operate on less than 1°C (less than 2°F ∆T)

[Senft, JR. (2007). Mechanical Efficiency of Heat Engines. Cambridge, UK: Cambridge University Press.]

Actually, I was wrong. Here is the actual reference:

Mechanical Efficiency of Heat Engines
Print publication: 13 August 2007, pp 153-162

Nicknamed the P-19, this engine has proven itself capable of operating down to a temperature difference of just 0.5 °C (less than 1 °F) between its warm and cool sides. The P-19 was the first to run from heat absorbed while resting on the palm of a human hand. The P-19 was first publicly demonstrated at the 25th Intersociety Energy Conversion Engineering Conference held in Reno, Nevada, in August 1990.

More about the P19 can be found here:

https://www.globalspec.com/reference/70 ... ing-engine

And the book can be purchased here:

https://www.cambridge.org/core/books/ab ... 25E39D91D7

An interesting feature of the engine is the mechanism for establishing a "dwell" period in the movement of the displacer. That is; a pause or resting period, while the displacer is covering / blocking the heat input.


I can't be entirely sure, judging from the pixilated image, but I think the loop at the end of the "lost motion link" would probably have the effect of only lifting the displacer up and away to uncover the hot heat exchanger for a relatively brief period of time, tugging the displacer up, then dropping it back down almost immediately.

This is an effect I've been trying to achieve in some of my experiments, (see here for example: viewtopic.php?f=1&t=5241 ) So, I just sent for a copy of the book to hopefully get a better picture and more information about this mechanism and the theory behind it.

Other than the counterbalance, having a simple loop in the connecting rod of an LTD type engine should produce the desired effect.

Something like this:


The displacer chamber of the P 19 itself has a very low profile so the displacer movement is limited to a very short distance.

Anyway, the point being, a typical medium size back yard compost heap can easily stay hot, at about 130° F for a month or more. That should be plenty of heat to keep any kind of LTD type Stirling running for that amount of time at least. The output might not be much, but running 24/7 could amount to some significant, useable power.

Augmented by water cooling from a cold running stream the power output could be increased.

As an aside, I recently visited the local village Depot behind the park where leaves are dumped in piles. We needed some mulch for our rose garden for the winter.

It was near freezing out and raining, but the leaf pile was still steaming hot just a few inches below the surface. I'm not sure how long that pile had been there but most of the trees in the village have been bare for a few weeks now.

Nice one, as i say short stroke and big bore is way to go.
Isn't the "dwell" period changing the time interval like a ross yoke linked?

Chris claims changing engine to ross yoke link improved efficency a lot
https://www.youtube.com/watch?v=LLzFi9aZcBM

Most popular '3 phase' (ross yoke linked) engine propably is the japanese model kyowa-gokin SE-905GB-HP or variants
https://youtu.be/mUzz2pPw2Pg

airpower wrote: ↑Wed Nov 17, 2021 11:20 am...
Isn't the "dwell" period changing the time interval like a ross yoke linked?

Not really sure what you mean, I don't really know anything about the Ross yoke, but as far as I know it doesn't effect any so-called "dwell".

Dwell is really terminology from internal combustion engines and in practical terms refers to the time period that the ignition points are closed or at rest, which doesn't really make sense applied to a Stirling engine.

Except in the sense of being at rest. In an IC engine the ignition/spark happens when the points open.

In a Stirling engine the displacer exposing the hot plate to introduce heat is analogous to "ignition".

The displacer of most Stirling engines moves in a sinusoidal wave motion, smoothly up and down with no resting period or "dwell" whatsoever. The unfortunate result is that the hot and cold air in the engine tends to get mixed which robs the engine of a lot of power, it is much like an IC engine being sluggish and lacking power due to the ignition timing being off.

Introducing a "dwell" meaning that the displacer is motionless, covering the hot plate, preventing heat introduction into the engine, provides a clearly defined "ignition" that can be more precisely defined and controlled to have maximum impact at just the right moment, only lifting the displacer, in order to deliver energy to the piston at the precise moment when it will do the most good.

I'm surprised to see that Senft was way ahead of me in that regard. The P 19 looks like it incorporated such "dwell", exhibiting much greater control over timing of heat input than the model LTD engines seen on the market today which seem to be exclusively sinusoidal.

The only real exception I've seen are the magnetic type LTD's.

Also some of the "flachplatten" type Stirling's by Ivo Kolin have a dwell, but neither of these are ideal IMO because of the limitations of the linkage used, also have an unnecessary COLD side dwell, leaving the hot plate exposed for an unnecessarily lengthy amount of time.

A simple loop in the displacer connecting rod, (as in my notebook drawing above) similar to the P19 "lost motion" linkage, I'm realizing just now today, could be a very simple way to introduce a dwell in a model LTD without necessitating any extensive modification.

With a simple loop in the linkage, the flywheel would only lift the displacer at a specific, limited time for some fraction of the revolution, so the moment and duration of the "ignition" (introduction of heat into the engine) can be precisely controlled.

To illustrate the difference, here is a drawing of the different displacer motion wave forms or motions.

Sinusoidal, "square wave" and the P19, which is much more on the order of an IC engine spark ignition system.

By cutting off heat input entirely with a "dwell" (no heat input period), during the expansion stroke (at the start of the power stroke), the remaining expansion will be entirely adiabatic (expansive cooling with conversion of heat into work). The engine runs cooler with less (or no) waste heat.

Also, no heat is let in during compression, which heat input at that time can only reduce power.

Of course, the time it takes for heat to propogates into the engine has to be taken into consideration, so the "dwell" should end, and heat be introduced a little before the start and into the begining of the power stroke.

A short stroke length (for the displacer) can help to facilitate rapid heat input, and a wide diameter displacer allows more surface area for a greater quantity of heat transfer in a short time period.

Someday, I may be able to use this creek behind our property (we own out to the middle of the creek) to test some large water cooled engine.

While this has become a great discussion of low temp differential Stirling Engines, I feel it's kind of strayed off the original topic, which is adding a cooling loop and heating loop to a Stirling Engine to maintain the cold and hot temperatures of each respectively.

While the P-19 is an innovative design, I doubt it can be scaled up to power a house, which is my goal.

JessIAm wrote: ↑Mon Dec 13, 2021 8:41 pm While this has become a great discussion of low temp differential Stirling Engines, I feel it's kind of strayed off the original topic, which is adding a cooling loop and heating loop to a Stirling Engine to maintain the cold and hot temperatures of each respectively.

While the P-19 is an innovative design, I doubt it can be scaled up to power a house, which is my goal.

A compost/creek is a Low temperature heat differential. So a low temperature type Stirling would IMO be the most feasible option. As a proof of concept, there are a few relatively high power LTD type Stirlings in the 500 to 2000 watt range.

Like this 1.8 Kilowatt LTD, which runs on a heating loop from a greenhouse and also pumps its own cooling water.


https://youtu.be/9Cy__Xsog2o


So, I don't see scaling up a P-19 type LTD to be as much of a problem as getting a high temperature alpha type engine to run on the kind of low temperature heat sources that have been proposed.

It might be possible, I don't know, but it is uncharted territory.

The point regarding the P-19 was that it only requires a 0.5°F ∆T to run, so certainly a Stirling engine of some kind could be capable of running on compost/creek ∆T.

Getting a low ∆T heat source to power a compact alpha type Stirling specifically is a bit more problematic.

Tom Booth wrote: ↑Tue Dec 14, 2021 5:45 am

JessIAm wrote: ↑Mon Dec 13, 2021 8:41 pm While this has become a great discussion of low temp differential Stirling Engines, I feel it's kind of strayed off the original topic, which is adding a cooling loop and heating loop to a Stirling Engine to maintain the cold and hot temperatures of each respectively.

While the P-19 is an innovative design, I doubt it can be scaled up to power a house, which is my goal.

A compost/creek is a Low temperature heat differential. So a low temperature type Stirling would IMO be the most feasible option. As a proof of concept, there are a few relatively high power LTD type Stirlings in the 500 to 2000 watt range.

Like this 1.8 Kilowatt LTD, which runs on a heating loop from a greenhouse and also pumps its own cooling water.


https://youtu.be/9Cy__Xsog2o


So, I don't see scaling up a P-19 type LTD to be as much of a problem as getting a high temperature alpha type engine to run on the kind of low temperature heat sources that have been proposed.

It might be possible, I don't know, but it is uncharted territory.

The point regarding the P-19 was that it only requires a 0.5°F ∆T to run, so certainly a Stirling engine of some kind could be capable of running on compost/creek ∆T.

Getting a low ∆T heat source to power a compact alpha type Stirling specifically is a bit more problematic.

Well defended! I retract my concern. :)

But the reality is the company how made the SunPulse SP-500 no longer exists and as far as I know the claimed power was never independent verified.
The engine has a diameter of 1300mm (51 inches) and models a tenth of the size dont manage a tenth of the power.

If for whatever reason, we were limited to using a higher temperature alpha engine, but only had some relatively low temperature heat source, some, possibly passive(?) or active heat pump, driven by the Stirling engine might be possible, to in effect, turn the diffused compost heat into a concentrated high temperature heat source. Of course, there would be losses involved as far as overall efficiency.

Basically, instead of an "air source" or "ground source" heat pump, a compost source heat pump.

https://opensourcemushroomdomehouse.wor ... pump-idea/

A Drawing from the article:


This is, again, though, a fairly exotic solution, but perhaps possible.

I've been meaning to pick up a compressor head for possible conversion to an alpha Stirling, just to see if it is really a practical thing to do. Another item on my long, Stirling engine experiments to-do list.

Not too hard on the budget, but the number of successful conversions I've actually seen is next to non-existent, though it is supposed to be possible


An interesting point made in the above article, (or perhaps it was in the accompanying video subtitles, I forget) is that more heat is generated by composting wood chips than by burning the same wood chips.

There was a French guy in the seventies driving his car and service his cooking, heating needs with homemade methane. It is made in a cylinder inside a compost heap. Temperature must always be above 20° (68) or thereabouts and a way to supply new material and let the used out. Lots of people in warm climate cook with methane from cow dung/urine. https://youtu.be/9F2rsoz56y4 Dont mix in your soap, detergent, washing powder..Small setup https://youtu.be/pKZgnXQCp98

A less dramatic way (if you live in colder region) is to make woodgas, it needs two things, wood(chips) and more wood(chips). Wood(chips) for the fire and wood(chips) in a container above to extract the gas from. Woodgas car in Helsinki https://youtu.be/esqma3ZI4CE People do have state approved systems working and sell excess electric.

The most sensible and long lasting would be Geothermal setup
https://youtu.be/MUWjjjFgXdg

airpower said: “But the reality is the company that made the SunPulse SP-500 no longer exists and as far as I know the claimed power was never independently verified. The engine has a diameter of 1300mm (51 inches) and models a tenth of the size don’t manage a tenth of the power.”
A tenth of the size in scale is actually 1/1000 the displacement. There’s something to be said for going big. As far as getting power from composting temperatures, I think something like the SunPulse engine would be a more likely bet than an Alpha. I concur though that I’d like to see independent verification on the power numbers.

Bumpkin

A system of the sort proposed here is apparently in production in Sweden.

With a capacity of "23,000 Stirling engines anually on the current production line."

https://youtu.be/LsTYALSu56E

These appear to be Alpha type engines, heated with a heat transport fluid (liquid sodium) circulated within heat storage "pods" containing a molten aluminium alloy.