My contribution to the ECE

[VincentG]

Here is a video demonstrating the relationship of pressure and displacer position. It seems to me this indicates a constant transfer of heat into the cold sink. So, without an intermittent heat source, any further improvements to heat transfer will just create a faster leak of energy. If there are any other explanations, I would be interested.

What's fascinating to me, that this seems to be the nearest visual I have seen of heat "flowing" as an energy.

https://photos.app.goo.gl/6gjxDnb4Sa4dzbzz8

[Tom Booth]

In comparison with your earlier video with the heavy weight and moving the piston a little more quickly, you've done a pretty good job of demonstrating the difference between adiabatic (with a load) and isothermal (with no load) expansion and contraction.

The former is more an oscillation ("adiabatic bounce"), the later more of a flow through of heat.

Adiabatic expansion/contraction processes generally are fast (not time enough for heat loss so there are gas temperature changes)

Isothermal slow, heat input/output and expansion/contraction are closely matched and gas temperature stays the same.

The balance and interplay between the various factors; adiabatic and isothermal, as well as work and heat input and output, loaded and unloaded can be quite fascinating.

[VincentG]

Fascinating is an understatement. I do wish there were more people experimenting with these engines as a legitimate green energy source. I am on some hot air engine facebook groups but most people are into the ancient relics and making scale models of old designs. There is obviously lots of room for improvement to be made.

[Tom Booth]

Fascinating is an understatement. I do wish there were more people experimenting with these engines as a legitimate green energy source. I am on some hot air engine facebook groups but most people are into the ancient relics and making scale models of old designs. There is obviously lots of room for improvement to be made.

I don't know if it is intentional, but IMO the work that has been done at the forefront of Stirling engine development i.e. NASA has been discouraging.

Millions and millions of dollars poured into R&D and the result: Nothing produced that anyone could ever afford. Like at best, $20,000 for a 1kw engine like this:

Resize_20230316_113453_3745.jpg (114.69 KiB) Viewed 3916 times

But to me, that is an awful design for a Stirling engine based on what my own kitchen table research has revealed.

Look at the, apparently copper cooling jacket in what looks like near direct contact with the heater head!

A really super duper effective heat sink drawing off nearly all the heat just to make hot water.

But that is the academic training, it's what the mathematics and computer modeling suggest I suppose, or is it intentional waste of research dollars to purposefully produce discouraging results?

Most people I think would criticize you and me for thinking we could do any better or improve upon what the best NASA contracted scientists and engineers have produced after decades with virtually unlimited resources at their disposal.

Anyone can get a 1kw IC generator on sale at Harbor Freight for $99

[VincentG]

I don't believe that is the pinnacle of the technology they had reached. It can't be.

I believe the hot air engine will have its day again. I have almost completed the design of my new idea and have started the first prototype. If my theories are correct it will have significant power and efficiency gains over any existing configuration. I'll start a new thread soon to document its development.

[Tom Booth]

I don't believe that is the pinnacle of the technology they had reached. It can't be.

I don't know. I've talked with several of the people very closely involved in the development and production of these NASA type engines and they all seem quite thoroughly indoctrinated into unquestioned acceptance of the whole Carnot efficiency doctrine and mathematics.

I've been told, the problem is, how to get the heat into the engine and how to get it back out again, as if the conversion of heat into work was inconsequential.

The insistence on the necessity for removing the majority of the heat input to a sink seems very deep rooted, and have spent hours in an effort to convince me of this supposed "fact" or "law of the universe".

So, the engines are designed accordingly, with something like 6000 BTU's of "waste" heat going to make hot water for every 1000 going to generate electricity.

[Tom Booth]

Take this thing for example, a Stirling engine for operation on the moon or mars:

Resize_20230316_141612_2888.jpg (80.37 KiB) Viewed 3910 times

The huge umbrella thing on top is to radiate "waste heat" from the nuclear reactor out into space. The upright posts, heat pipes to transfer the excess heat away. The whole thing seems designed around the idea of throwing away as much heat as possible.

It's "accepted science" and to suggest otherwise is considered "pseudoscience".

[VincentG]

That may be spot on Tom. By coincidence, I was listening to an episode of the Lex Fridman podcast with Tim Dodd. Tim was talking about how the NASA engineers enjoyed working with space X because they were forced to make huge leaps in design theory and evolution of ideas without dealing with all the red tape and protocols typical of a NASA project.

So maybe the Stirling program there was unable to evolve beyond the basic concept of the Stirling cycle. We all know how effective the government is at running things.

[gitPharm01]

Since you mentioned that you are capable of CNC and other machining technique, I think this well-documented model will be beneficial:
Mini-Ecoboy :
Link to Ecoboy

This is a 50W Stirling engine and you can check many aspects of this model on this page.
The most valuable thing is a complete set of CAD files for its parts:
Drawings of Mini-Ecoboy

According to the author of this page, the model is designed to be easy to build.
If you want to go one step further from educational models, this might be handy platform to test your concept on improving Stirling engine's performance.

This is done by Dr Koichi Hirata, he works for National Maritime Research Institute.
He made a website called Stirling Engine Dictionary.
This site has a English version:
https://www.nmri.go.jp/archives/eng/khi ... dex_e.html
But unfortunately, not all of its contents are fully translated into English.

[VincentG]

gitPharm01, that is a great resource. I'm sure it will be of help. Also an impressive engine, especially the 100w version.

[gitPharm01]

gitPharm01, that is a great resource. I'm sure it will be of help. Also an impressive engine, especially the 100w version.

I am glad to hear that.
From that Stirling engine course I've been translating, I learned that it is important to have a well-documented model in experiments.
Almost all experimental models built by the professor( while he was a student in university) failed in their first run.
These models are not randomly made but designed through careful calculations and simulations.
However, some friction on several spots of the engines could easily cripple them.
And since these models are well-documented, he and his teammates could locate these problems easier and faster.

Another surprising thing I learned from the course is that syringe pistons actually have the least leakage problem compared to metal pistons.
You can see this result in the attached picture.
So if you are moving from educational models whit syringe pistons to models with metal pistons, please do check about the leakage of working gas.

[Tom Booth]

(...)
These models are not randomly made but designed through careful calculations and simulations.
(...)

I do consider good record keeping valuable, (why I almost always video record experiments on the first trial) I tend to disagree with this approach that has been emphasized as the only way repeatedly through the series. Using calculations and simulations alone can indefinitely perpetuate past errors, as the saying goes: garbage in garbage out.

In my research I've talked to professionals in manufacturing of refrigerators who have confessed to me that for things involving complex fluid dynamics, like heat pumps and refrigerators, mathematics and computer modeling is not up to the task. They mostly use trial and error.

At the time I was making these inquiries I was trying to design a combined Stirling engine / heat pump so I was calling the various manufacturers with questions and they would put me on the phone with their engineers and kept running into the same response. For things like condenser and evaporator tubing lengths, actual refrigerator manufacturers rely on trial and error.

Try a long pipe, medium pipe, short pipe... See which works best try large diameter, small diameter etc.

Random experimenting can often, in my own experience, turn up insights and new directions for research that might not otherwise ever be discovered.

Think outside the box, as they say. Heat engine research has remained almost completely stagnant for 200 years with little innovation, progress, development, or major breakthroughs of any kind. That doesn't happen by strictly playing it safe.

[VincentG]

I agree Tom, I think a good mix of math and real world testing is important though. To gitPharm01's point, having a working model to test is crucial. I am glad to have started with the engine I did, being so easy to make changes to.

I was thinking it would make a cool engineering school challenge to start with that particular LTD and have an output contest, using a particular generator and drive system, with fixed variables of the crank, piston and cylinder. So stock parts from the top plate up. Anything else can be changed, including air ports, valves, and displacer chamber volume.

The competition could be for max rpm or watts across a fixed electrical load.

[Tom Booth]

I agree Tom, I think a good mix of math and real world testing is important though. To gitPharm01's point, having a working model to test is crucial. I am glad to have started with the engine I did, being so easy to make changes to.

I was thinking it would make a cool engineering school challenge to start with that particular LTD and have an output contest, using a particular generator and drive system, with fixed variables of the crank, piston and cylinder. So stock parts from the top plate up. Anything else can be changed, including air ports, valves, and displacer chamber volume.

The competition could be for max rpm or watts across a fixed electrical load.

I don't know if they have changed over the years, but I had a real problem with the crankshaft held in place by tension between the two uprights. If it wasn't tight enough, the whole crank assembly would fall out. Too tight and there would be too much friction, It seemed nearly impossible to get the thing to run consistently. Personally, I think what you've been able to accomplish borders on the miraculous.

After the first one melted down, I eventually got another. I wanted to try running it on ice to demonstrate to someone how that was possible, but I wasn't able to get that type of engine to run on just ice. At best it would turn over a few times before quitting.

I also don't like the way it's put together generally. Parts riveted or tack welded together. I gave up and sent for a model that was easier to modify. You've managed to work wonders with it though.

[VincentG]

 I wanted to try running it on ice to demonstrate to someone how that was possible, but I wasn't able to get that type of engine to run on just ice. At best it would turn over a few times before quitting.

You're right it's not a very good model to start with. It needs a pretty large delta t to run well and at higher power levels friction is an issue.

What engine do you use now?