Free Piston engine for more cheap energy than the Rhombic Stirling to support solar and go off grid?
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- เผยแพร่เมื่อ 16 พ.ค. 2024
- In this video I show you the beginning of the investigation into which Stirling engine concept could become the successor to the Rhombic Stirling.
The Stirling engines I have built so far are too complex for energy self-sufficiency and therefore too expensive and maintenance-intensive.
I would now like to extensively investigate which engine concept would be best for my next project to support the solar plant in times of low sunshine!
Free Piston Stirling engines do not have a kinematic drive mechanism and are therefore much simpler with less friction and wear.
They require no rolling or plain bearings and the only moving parts are the piston and the displacer.
Free Piston engines are available in many different versions, some of which are maintenance-free and extremely durable.
The very first Free Piston Stirling engine was described in a British patent of 1876 by Davy Postle.
Modern Free Piston Stirling engines are associated with the names William Beale and Sunpower.
They commercially marketed the Free Piston Stirling engines and pushed its development very far.
Nowadays, Free Piston engines are mainly used as refrigeration machines in cryogenic systems.
Free Piston Stirling engines have no kinematic mechanism coupling the reciprocating elements to each other or to a common rotating shaft.
This eliminates the need for bearings and simplifies the engine to a great extent.
The piston and displacer move entirely in response to the working gas or other spring forces acting upon them.
The Free Piston engine is a dynamic, resonant system operating at a more or less constant frequency and is self starting.
It requires only a slight, random pertubation to set it in motion.
There are no major side thrusts on the piston and displacer which relieves the lubrication and wear problem sufficiently to permit the use of gas lubricated pistons.
The cylinder can be hermetically sealed which is also an substantial advantage oft he Free Piston concept.
Another important characteristic of Free Piston engines is that they are more or less self regulating.
In addition to these advantages, the Free Piston Stirling also has some drawbacks:
The lack of a rotating shaft makes it necessary to use the motion directly or to employ a linear generator.
Free Piston engines do not have heavy piston side forces or other demanding bearing requirements.
The resulting possible use of gas lubricated bearings are characteristically high precision components with very small clearance.
A piston running exactly centrical is also not easy to achieve and must be ensured by precisely coordinated measures.
In engines of substantial capacity the spring forces involved are so great that mechanical springs would need to be so massive as to dominate the system.
Gas springs on the other hand have hysteresis and leakage losses and they do not provide positive suspension when the engine is not running.
The analysis of Free Piston engines is complicated by the fact that the dynamics of the piston and displacer are caused by the fluid processes their motion causes.
This leaves fewer known starting parameters and therefore the analysis more difficult.
Free Piston Stirling engines utilize the prinziple of vibrating systems.
The necessary requirement for the operation is the dynamic equilibrium of forces.
The resolution of the complicated interdisciplinary actions inside a Free Piston engine is complex and best approached numerically on a computer.
The vibration theory and the analysis of linear and non-linear systems is a difficult subject to handle.
The involved several masses with multiple springs and damping devices don't make things any easier.
Free Piston Stirling engines involve few moving parts and appear to be quite simple and straightforward.
Their proper design and operation requires substantial engineering expertise and a very high level of craftsmanship.
The advantage that they do not require a kinematic drive mechanism is partially negated by the problems of piston centering and balancing the forces.
The major problems I had with the Rhombic Stirling with friction, wear and leakage of the piston running surfaces would also continue to exist with the Free Piston Stirling.
The Free Piston Stirling also involves difficulties in design and production that I can hardly estimate and that could prove to be unsolvable.
The uniquely elegant concept is very promising but the more I have looked into it, the more my doubts have grown as there are many complexities.
What do you think of the Free Piston Stirling, please let me know and write your opinion in the comments.
Thank you very much for your attention!
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I have built a few free piston SE's and to be honest they are very simple and all the positives you mentioned are true. Don't think too much about it, just start and make a few, you will end up learning so much and fall in love. It took me two years to get to a level where I feel very confident and satisfied with my final build.
Did you use a diaphragm or a classic piston and displacer?
Sounds nice, thanks!
@@myengines2443 I use a diaphragm and to be specific I found that the donut/cupcake rubber is a solid choice as it can take high heat and is strong enough not to break...
Both concepts sound really interesting for me!
I will think about it and put it on my list!
Thanks
I find the FPSE very promising - supposedly one was already proven to have run several years without any maintenance at all. If there was any engine design to switch to, this is the one with the most promise. The idea of one service cycle for a decade is incredible!
Unfortunately I think the classic Free Piston Engine is to complex for me.
Maybe a low tech variant with a diaphragm piston may be possible?
So how about an opposed dual piston FPSE, where the driven pistons are connected and the displacers are connected. There will include an external regenerator that connects both sides of the FPSE, therefore it cuts out the need for springs or diaphragms. If you are looking at springs why not use repulsive magnets i think they would act as a very powerful spring in the right magnetic orientations.
I think the opposed system could work better and it can be coaxial, so you have the displacer with its own connection rod to one another and the driven piston connected by its own connection rod.
Although the problem i see here, is the massive vibration from the system and whether the linear electric generator can compete with rotational generators, so probable a scotch yoke or external crank could work. Lastly another problem still maybe lots of ware.
Love watching this channel!
Thanks for your nice help!
This sounds interesting and I think I saw something you describe in one of my books!
I will look for it and report!
Happy to see from you again with. As usual a very good content.
What about controlling the displacer with linear motor or voice coil? At resonance we just need to compensate the losses.
Having two sets of spring to hold a moving mass will provide opportunity to control the resonance frequency. Stretching the spring apart can help in controlling the resonance. ( It is like attaching springs to a from both the sides. And tightening them by stretching as in string instrument. ). Electronically controlled linear actuator can be used to control the tension..
Electronically controlling the resonance of piston, displacer and displacer moment will give lot of flexibility in tuning 😊
Sounds nice but also very complicated, I have to think about it!
Many thanks for your great help!
A very good level of analysis
Thanks!
great stuff man
Thanks!
There is a flat spring cut into spirals that actually creates a seal when in its neutral state.
221 in general, the operating speed of a prime mover is Determined by How it's Loaded. in other words, the (desired) under-load speed of the prime mover is determined by its output, the load, and by the power take-off mechanism. in the case of a prime mover whose output is low torque, the use of HIGH ratio reduction is called for. preferably in a Single stage. doing this has the affect of partially isolating the prime mover from the load.
i have previously explained why the rhombic LINKAGE is a non-starter.
Thanks for your analysis. Magnetic springs would be interesting.
Now that you mention it, I'm surprised I haven't read anything about it.
I'll think about it and find out, maybe there's a reason.
Thanks for your nice comment and the good food for thought
free pistons can potentially provide a much greater surface area and compression. It can also run at way higher pressures, altering the PV graph thus increasing the efficiency.
Yes the Free Piston concept is nice but a high tech engine as you describe is very complicated and really would take a long time to develop.
Maybe I try a low tech version first and the see...
Have you considered Allan Organ's half-rhombic design where he uses half of the rhombic drive, and two linkage arms to make a simpler Stirling engine? This doesn't solve the problem of seals, but it seems to simplify the kinematics. He describes the details in his latest book.
Yes, I talked with him about it and also built a half Rhombic engine.
If you look for older videos of me you will see it!
Thanks for your suggestions!
Hmmn! I think the free piston concept has a good future. But they require complex analysis and design, and must be manufactured to very precise tolerances. Only you can know if you are capable of working to that level of precision.
Unfortunately I don't think so but the idea of a low tech free piston engine with a diaphragm may be a possibility?
@@myengines2443 That sounds like a viable option.
Very good description, it is very difficult to "build by yourself" a free piston stirling, that could be' practical for generate a decent ammount of power. (I like to be' involved/informed for a potential indipendent small projet)
Yes, I also think that and at the moment I prefer a low tech rubber diaphragm FPSE.
But I am not sure if it can produce reasonable amounts of energy.
Thanks!
@@myengines2443 let us know the "evolution" the calculation is very articolated 🤞
In this case i go and buy a box of beer (better 2 or more) and organize a brainstorming session with my colleges. 😂❤
Unfortunately, my friends don't have the slightest idea about energy-generating engines!
Have you had a look on barumman's thermomechanical sterling? He is showing some decent details in construction and building this kind of machine. He achived arrond 5W output. So the amount of effort isn't in a good proportion to the expectible output. This machine is based on old plans from very reliable power sources for light buoies before pv became the standard... Keep on, please!
Thanks for your nice comment!
And yes I am in contact with barumman and used some pictures of his engines as you can see in my video of the Thermo Mechanical Generator a few weeks ago!
Nice video! I don't have enough knowledge about the free piston Stirling engine to form an opinion worth sharing. But I can write a comment to help feed the algorithms anyway, and I am curious if a linear generator can be designed so that magnetic forces help keep the moving part centered, without too much difficulty or functional drawbacks.
Yes, to use the linear alternator also for guiding and damping the piston is a good possibility.
Thanks!
Hi, your series lloks interesting. I'm truying to assess what would be needed to get a 100w generator in order to power the house on nights. I definitely would like to see a free piston generator performance around 100 w output. Hope you're going for it. Rgds
Thanks for your kind comment!
NASA KiloPower FPSE for Artemis Moon Missions use such technology to turn nuclear fission heat into electrical current power to energize the moon base.
Yes its nice but very high tech where money does not matter
I like idea to use linear generator as starting force for FPE. Just apply the voltage and piston will compress gas.
Yes, the nearly self-starting possibility of the free piston Stirling is amazing!
These analysis videos are great.
Are you more doing this for the fun of building your own engine or just trying to solve the problem of producing power? I have one of the FPSEs shown at 0:44 (and 2:00) that I could sell if you are interested. Rated for 1kWe max, although shipping might be an issue as it's ~50kg.
Both, building engines is my hobby for years and since the electricity bill raised so much its very interesting to support our solar plant with a generator in winter.
We have wood and biogas which fits perfectly to a small Stirling.(look at my older videos)
Your Microgen is very nice, but shipping would be overkill.
Thanks and best wishes
This is the only one of the alternatives you have looked at capable of producing the amount of power you are looking for. And there are commercially available products to look at and copy. So.... they are the only alternative where you don't have to do complicated and hard development work to get to the end result. Just copy the design from Microgen, there are drawings out there of it. So it's a simple case of reverse engineering. This could be a community effort, and I'm interested in cooperating, I'm able to contribute with the CAD-modelling. I also have a workshop capable of building one, I only need more spare time to be able to realize something like this. A community build would certainly spark my interest, and possibly be what makes me take the step and try to build it myself.
That is with the above mentioned design for me though. For me it's this exact method or nothing. I'm not considering other designs as there are no proven designs available to copy.
And also, this is the only one which have a decent chance of producing the power level I'm after (which I expect to be the case for you too).
Also, I still don't understand why you are so reluctant to this class of stirling engines. You seem to have made up you mind that this particular design is to complicated before going in to this, looking for excuses to back up this conclusion. The other design you have shown look to me to be a lot more complicated to even start to move. With this specific class of design you have several publicly available designs that are known to work, requiring no development work from your side. Sunpower, NASA and many others have published loads of data and design details on this class of Stirling engine. So this should be a case of finding the information needed and executing it. None of the other design classes have this going for them.
The problem you mentioned with excessive leaking around the displacer due to lower accuracy of machining will in this design only play a minor role compared to the other classes. This is because this is the only one with no side forces acting on the pistons.
BTW, achieving very accurate internal and external cylindrical surfaces are shown in great detail by Robin Renzetti (Robrenz), look at his video "MAKING AND USING LARGE DIAMETER LAPS", With this method you will be able to achieve the required precision with no problems! So.... this is NOT a premise for dismissing this class of stirling engines! Although you seem to make it one of the major reasons for not going this route.
I didn't want to badmouth the free piston engine with the video, but I think there are just too many imponderables for hobby building.
The Rhombic drive also has no piston side forces and I have massive problems with piston wear.
It would be no different with the free piston Stirling.
The difficulties lie in the details, such as the piston centering problem and the design of the spring and damping forces, which are also not explained in detail in the machines built.
Your arguments make me think seriously about the free piston engine again, that's the point of the videos.
Thank you very much, hopefully we'll keep talking!
@@myengines2443 Wouldn't it be a good idea to use diaphragm for the piston which needs to seal? I think that someone above mentioned it. And there is one great stirling engine pioneer on youtube. His name is Shane Pomeroy a nd he used to have similar problems with pistons and leakeges like you. So he is developing diaphragm stirling engine and he had great results even when he is using diaphragms on the hot side of the engine. Free piston engine does not have piston on the hot side so that should not be a problem. My english is not perfect but I hope that you got the point. Thank you for your development effort.
@myengines2443 I hope you consider my thoughts seriously, and understand I have spent years thinking and pondering about this very thing!
About the side forces and wear on the piston. You CAN NOT compare the Rhombic drive with a FPST in this regard! Only the FPST have the possibility to use active hydrostatic bearings to prevent the piston from ever touching the wall. This is a truly tested and verified design in real life. And the Microgen design I keep coming back to use it. So.... you can be expecting to solve this problem 100% by going for this design.
The rombic design still require piston rings, this is also confirmed by all available designs out there. And since you have already proven you are not able to make this work you should have your confirmation the FPSE is more suitable for your needs.
NASA have also come to this conclusion.
About the springs, there are detailed papers in the free domain explaining this very well. Reading them made me think this is solvable for a DIY'er like we are.
I have previously tried to post links to these papers here, but they are blocked. Contact me and I can send them to you. I'm sure you will see this is doable when you see the papers.
Also, there is a paper describing the building of a very simplified and very much easier to build version of the NASA design. This proves it's possible to simplify things in order for us to build something like this and still make it work. Again, contact me and I can send you the article so you can see for yourself.
And also, the Micro gen design have simplified both heat exchangers to a point where they are possible to be mass-produced. A.k.a. possible to be built in large numbers, without needing crazy tolerances not possible for a DIY'er. No welding of small tubes, and no machining techniques that you haven't already managed.
So, I suggest going forward to make a detailed list of possible problems. Then we can discuss in detail which problems are possible showstoppers. If then at the end we find any that are clear cases of issues with no possible solutions that we can solve then you should start looking for other design classes. But my years of thinking about this design on and off indicate there are no unsolvable issues with this design.
@@spamspammesen5970 you find my email adress on my youtube channel page in the description.
It would be very nice if you send me some links or the papers directly!
The vibration theory involved with the several masses with springs and damping forces is very complex that I am a bit afraid of.
May be a low tech free piston engine with a rubber diaphragm is a possible way?
Many thanks for your help!
As I said use an high-pressure Alpha piston engine, dude!
I am not sure about the endurance properties of such an engine!
🎉🎉🎉
Thanks!
Travelling wave engine has no moving parts
Yes, I also think about it a lot.
Please watch my video a few weeks ago for many details about it and write your opinion plz!
und wenn du's tatsächlich schaffst, dann hüpft dir das ding vom tisch.
einzige lösung boxer-anordnung...
nur eins der weiteren probleme.
Auch das ist noch ein Nachteil!
Danke für deine Gedanken!