LTD magnetic vs gamma

[Tom Booth]

I'm assuming you mean under-damped? Only because I can't find any references to "under-dumped" electrical oscillator. (and the spell checker on my phone is trying to be so very helpful in the same way)

Having little knowledge of electrical circuitry, would that be a sustained or continuous oscillation?

I think most Stirling engines with some form of direct electrical generation use an alternator, that is, with a rectified circuit. To turn the high, low or whatever frequency output to DC (then back to AC with an inverter. Probably.)

So, by "no piston", you really mean diaphragm or bellows piston?

Having a displacer driven by an electrical oscillator, which oscillation itself is generated by ? What?

There are "thermoacoustic" Stirling engines with a magnetic piston that passes through a coil. There is only one moving part. Those engines though, have no displacer.

It sounds like you are talking about something with some sort of feedback loop, so the AC power generated drives a displacer? Some electrical/mechanical harmonic.

I'm not getting a completely clear picture of what you have, or had in mind, and I'm not sure if the picture is stable or morphing and evolving.

There may be some novel idea there somewhere, or you might be talking about something that already exists.

[omblauman]

Un underdamped electrical oscillator is the equivalent of a mechanical pendulum, an oscilator which doesn't loose too much of its energy per cycle.
In our case the sterling cycle would compensate for the electrical losses driving a coil and the electrical circuit would provide the inertia normally supplied by the flywheel to drive the displacer with the correct phase. A way to reduce the number of moving parts. I have never seen anything like it but I know little of the sterling world.

[Tom Booth]

Un underdamped electrical oscillator is the equivalent of a mechanical pendulum, an oscilator which doesn't loose too much of its energy per cycle.
In our case the sterling cycle would compensate for the electrical losses driving a coil and the electrical circuit would provide the inertia normally supplied by the flywheel to drive the displacer with the correct phase. A way to reduce the number of moving parts. I have never seen anything like it but I know little of the sterling world.

Very interesting, and good explaination.

The goal or intention of reducing the number of moving parts, though may be difficult, as what is less than one?

This example for instance:

https://youtu.be/DyPxNNJQo9M

The same guy later added a linear generator.

https://youtu.be/cAyw_dOioMU

In the case of this kind of engine I guess it could be said that the wad of steel wool (or "regenerator") in the test tube acts as a kind of thermal flywheel.

I like your idea, very much, though, I'm also struggling in my mind to find a practical way to incorporate it

If the proposition were possible, in one way or another, I'd assume such an engine, of necessity, would operate at a rather high frequency.

I would also assume there would be a need for some form of condenser/capacitor in the circuit somewhere.

What happens if the rate of oscillation changes? More or less heat is applied, or a load is added or taken away?

I have a gasoline generator that had a capacitor that exploded and needed to be replaced. I think that was attached to some controlling circuit board (I'm guessing), that's about all I know. In that case, a load, added or removed, is not a problem, I guess, but I really have no idea what that capacitor was for, or how complicated the circuitry might have been, but my generator quit working and I had to replace the capacitor which was ozzing some black goo.

The Bedini circuit pops into my head, though I only have a vague idea what that is about. Some sort of "free energy" quasi-perpetual self charging circuit I keep running across on YouTube:

https://youtu.be/DFwY6VQhOfw

[omblauman]

The goal or intention of reducing the number of moving parts, though may be difficult, as what is less than one?

I would also assume there would be a need for some form of condenser/capacitor in the circuit somewhere.

What happens if the rate of oscillation changes? More or less heat is applied, or a load is added or taken away?

With a low temperature stirling generator in mind, i.e. very low power density, the goal to reduce parts is also to reduce friction and the Electrical LTD might be ideal since the generator part requires coils anyway. Yes a capacitor is needed, I can't think of any other way to make an electrical circuit to oscillate. There is in principle only one oscillator in the system, the LC oscillator , so there shouldn't be any problem of frequency adjustment, if would be easy to tweak it if needed anyway. Not completely true if the membrane is elastic, the mechanical oscillator made by the mebrane and the engine volume should have a much lower natural frequency in this case.
'Happy to know that you want to think about it too, let's try to design together something in principle.
The starting point seems to me a standard LTD displacer chamber where the floating foam displacer is unstable to start with, we have to think about a way to drive it magnetically which keeps it away from the wall too. The horizontal membrane attached to the generator coil seems more straightforward and the LC circuit is part of the generator coil. Need to go now, o.-

[Tom Booth]

"There is in principle only one oscillator in the system, the LC oscillator , so there shouldn't be any problem of frequency adjustment"

I guess this is, or could be true.

My familiarity with coils and condensers is mostly confined to old Briggs and Stratton lawn mower type engines where a magnet on the flywheel passes a coil to charge the condenser, which then holds the charge until the points open, so, in that circumstance, there is really an independent charge and then discharge, which is not really an oscillation, though, in my way of thinking, the spark/ignition in an IC engine is analogous to the delivery of, or exposure to heat by the displacer movement.

In other words, control over the timing, in my general experience, involves introducing some delay in the discharge, which in this case would, presumably, activate an electromagnet to lift a displacer rather than jumping a spark gap.

I can rather easily imagine some such Briggs type magneto system adapted to a Stirling, but when it comes to some free oscillation I'm at a loss.

[omblauman]

the RLC oscillator basics are here:
https://en.wikipedia.org/wiki/RLC_circu ... %20circuit.
I would start building just the displacer chamber and measure losses in the displacer coil and pressure outputa, powering everything with an amplifier. This would give us an idea if it could work at all and how to design the generator

[Tom Booth]

the RLC oscillator basics are here:
https://en.wikipedia.org/wiki/RLC_circu ... %20circuit.
I would start building just the displacer chamber and measure losses in the displacer coil and pressure outputa, powering everything with an amplifier. This would give us an idea if it could work at all and how to design the generator

After "I would start building just the displacer chamber" I'm lost.

By "measure... pressure output", I'm assuming you mean air pressure, from heating and expansion of the air in the displacer chamber.

By losses in the "displacer coil", I'm not sure what you mean, or how that might be accomplished. Is there one coil acting as a generator and another as actuator, or does one coil do double duty? I have no real idea about what physical arrangement of components you have in mind.

Edit: As a kind of quick and dirty - something to begin with, possibly, that might at least work, is take a regular off the shelf LTD engine, stick a magnet on the flywheel to pass by a coil to activate a solenoid directly to trip the displacer.

Timing can be adjusted by moving the magnet on the flywheel, or by moving the coil...

On the other hand, it might be just as well to position a magnet on the flywheel in such a way that it will lift the displacer directly as it passes by above it. More or less the same as existing magnetic LTD engines, but with some ability to adjust the timing by repositioning the magnet one way or another.along the circumference of the flywheel, rather than having the magnet attached to the piston.

If there is any advantage to some timing, different from the usual fixed placement on the piston, that might at least provide a clue.

[omblauman]

what looks to me the most original, least known component of such an engine is the displacer so I would start analyzing its properties first.
The drawing shows a typical LTD foam displacer contained in its clear plastic box, circled by a metal band, L2, to push it up from the box outside with the driven loop L1.
The first problem is that the current decay time constant , K column in s, in the loop (independent from the number of turns) is barely sufficient even for a ridiculously heavy loop around the displacer. Most of the weight could be taken care with a spring. R loop radius, a wire radius, rho = resistivity, L inductance.

IMG_20210403_131455520.jpg (154.6 KiB) Viewed 3333 times

I need to check what happens by adding a thin steel disc to the bottom of the displacer. What about small radial permanent magnets lifting the edges?
I am stuck right from the beginning.

[Tom Booth]

One fairly common method of dealing with the weight of a large displacer, in an LTD type engine is to turn it on end sideways and either balance it on edge or hang it on some sort of hinge where it can swing like a pendulum

The displacer chamber itself,using such a method is usually somewhat tapered / wedge shaped, narrow at the balance point or hinge and wider at the opposite end

https://youtu.be/9Ckd7N3MxUU

https://youtu.be/4sV_0xKX4II

I had a need for some such arrangement when designing a Stirling wood or coal stove engine. I thought the displacer would need to be rather heavy, constructed from some type of refractory cement or firebrick . Turning the displacer on edge in theory, would help to eliminate the weight problem.

Hinged displacer

stirling_stove.jpg (26.34 KiB) Viewed 3329 times

I have a wood/coal stove that I have plans to adapt in some such a way sometime.

[Tom Booth]

As far as your drawing; I'm not familiar enough with electronic circuits, and the technical terminology involved to know or understand what is the intention

Looking up "current decay time constant" doesn't really help me. What is the consequences of that being insufficient? Insufficient to accomplish what?

My best guess is that this is some sort of electromagnetic coil for lifting the displacer

All the coils I've ever been familiar with for any purpose have always been very tightly looped.like this solenoid:

Solenoids1-300x199.jpg (11.8 KiB) Viewed 3314 times

I don't know the numbers or other technicalities involved but my common sense suggests there is probably some practical reason for such a compact form and would start with some available off the shelf coil and design the engine around that rather than vice-versa.

Would doing something like the following make a difference?

IMG_20210404_114206799_resize_42.jpg (28.42 KiB) Viewed 3315 times

[omblauman]

" Looking up "current decay time constant" doesn't really help me. What is the consequences of that being insufficient? Insufficient to accomplish what?"

My thinking was that the oscillator circuit of which L1 is part would have induced a current in the short circuited coil of the displacer L2 repelling it towards the top of the chamber but the current seems to decay too rapidly to work at typical LTD frequencies. On the way down gravity and a spring would push the displacer while the reverse current is stopped by a diode. At a certain frequency this scheme becomes very efficient because electric energy has nowhere to dissipate, it can only slosh back and forth between electrical and mechanical, this high efficiency is what we should aim to. Dissipation on the mechanical side would only be aerodynamic, little we can do about it.
A superconducting displacer would work well here but obviously is not an option in a thermal engine.
A sucking solenoid like you are showing could perform the same function attracting instead of repelling the displacer, I need to calculate weights and powers in this case too to see how energy efficient it would be. In this scheme the length of the core with respect to the solenoid is certainly relevant, I need to think about an optimum length/location.

" All the coils I've ever been familiar with for any purpose have always been very tightly looped.like this solenoid:"

The number of turns is not relevant at this stage what matters is the total weight of the copper. At the end one chooses the number of turns to be a comfortable number for the rest of the circuit to work efficiently.
A third way would be a solenoid with a permanent magnet core.
Another way would be peripheral linear motors.
In all systems the displacer driver and the generator coils could interact strongly, or even coincide, but i still contend that designing/experimenting with the displacer separately at this level would tell us more than adding all complications from the beginning.

[Tom Booth]

I've seen a number of Stirling engines that operate at what seems to me, very high frequency, generally of the "free piston" sort and very short stroke of the displacer.

https://youtu.be/QcppEhp2RfA

[Tom Booth]

"the oscillator circuit of which L1 is part would have induced a current in the short circuited coil of the displacer L2 repelling it towards the top of the chamber"

Just out of curiosity, or perhaps ignorance based skepticism, I don't think I've ever seen an example of any such repulsion from an induced current such as you've described. For all I know, there are examples to be found all around, but none come to mind.

An AC induction motor, being the closest thing to this as I'm able to come up with, as I understand it (or don't) involves a coil, inducing a current, but this does not result in motion until a second out of phase coil is introduced to attract the induced magnetic field.(or does it?)

A simple homopolar motor will turn continuously, but an AC coil that just lifts and drops another coil, or metal ring or whatever, I'm not sure I've ever seen.

I guess my question is, apart from any association with Stirling engines or displacer, is this an actual proven phenomenon or something entirely new and/or theoretical?

[Tom Booth]

The term "linear motor" came to mind to describe what it seems like is sought after (sort of, maybe)

Searching on that term turned up this video, which, if not specifically related, is at least interesting. Particularly when using gravity.

A solenoid and magnetic switch:

https://youtu.be/wHdFdw1hLzE

[omblauman]

The first video you sent is super interesting and the model shown is pretty sophisticated, worth understanding in depth.

"Just out of curiosity, or perhaps ignorance based skepticism, I don't think I've ever seen an example of any such repulsion from an induced current such as you've described. For all I know, there are examples to be found all around, but none come to mind."

It's the simplest electrical "motor" one can think of , like all others it's based on induction. The L2 induced current opposes the flux of L1, until the L2 current decays resistively in an L/R time the displacer would repel and stay away from L1. With a superconductor one could levitate the induced current conductor forever. In my scheme, which was just the first thing coming to mind, the temporarily levitated displacer would fall back down periodically to keep the cycle going, without a mechanical connection.

The linear motor of the last video is a very inefficient motor example, a suction solenoid only pulls an asymmetrically placed magnetic iron core, like in a door electrical unlocking device or in many electrical relays. When the core is all inside the solenoid the attractive force stops and what does something are just the asymmetries of the two permanent magnets and their springy repulsions, i don't find it inspiring in any way.

The clever design is the one of the first video, I am trying to understand if one can do something similar in the unsophisticated LTD category.
As you might have noticed the clever part is all in the way the displacer is handled, the generator part is straightforward, your proposal of using a solenoid, with or without a spring, could be a good starting point. The spring would allow a faster pace, not important for the per-cycle efficiency, it could be added later. To start I don't see anything else other than calculate electrical forces and energies to compare them with the ones available from the stirling cycle.