large lamina flow build

[Tom Booth]

This is not the video I was looking for, but the jug video was similar.

A weight was dropped down the neck of a jug and the air cushion in the big bulb of the jug, caused a similar pogo or bounce effect, but with no application of any heat at all.

https://youtu.be/20XcCHnynDY

[Sockmonkey]

As the power stroke in engines like these is less powerful than traditional combustion engines, you could probably get away with using desmodromic cams instead of a crankshaft for both the piston and displacer so their movement and dwell time allows for maximum heat exchange.

[Tom Booth]

Maybe.

I was thinking just a simple grove cam, possibly cut right into the flywheel, just for the displacer.

Something like one of these:

https://youtu.be/UZ8JkMHpsiE

https://youtu.be/DapbPNaIGVY

I can't really picture or imagine what advantage there might be to having the power piston on a cam, or how that would work.

The second one has fairly sharp transitional phases with fairly long dwell time. Just about exactly what I think would work well for controlling displacer motion.

I think such a groved cam could easily be incorporated into a normal LTD type engine.

[Sockmonkey]

I can't really picture or imagine what advantage there might be to having the power piston on a cam, or how that would work.

Using a cam for the power piston let's you tailor it's motion and dwell time for maximum efficiency. Same reason you want it for the displacer. Some four-stroke engines have been made that way, but they have problems with cam wear because the contact area is so small. With stirlings, mansons, and lamina flow types, the power stroke is much less powerful for the size of the engine so you can probably get away with using cams.

[Tom Booth]

I would want a cam for the displacer because the displacer is the mechanism used for delivering heat to power the engine and the heat input needs to be timed like the spark in an IC engine.

The displacer is designed to be very light so it can be easily moved carrying little momentum or inertia.

The displacer is not intended for transmuting any mechanical energy. It doesn't drive the engine or any load, so loses from friction are minimal.

None of these things are true for the piston. The piston transmits power, is relatively heavy, has momentum and inertia, sudden changes in motion and direction are detrimental, it transmits mechanical energy, anything that would interfere with it's smooth natural movement would tend to create a great deal of power loss and unnecessary friction and wear. There is no reason to interfere with it's movement and it has no, or God forbid, SHOULD have no "dwell" whatsoever, which is a complete stop. Why would anyone want the piston to remain motionless for any length of time?

Having the piston on a cam could produce no advantage whatsoever and could only be detrimental, as far as I can see.

Also, assuming it to be true, that some engines have been built with the power piston on a cam, the problem we are trying to remedy by putting the displacer on a cam, (lack of power, low torque) if successful, would introduce the same problems mentioned: cam wear, among other things.

I think the most efficient engine is a free piston engine driving a linear alternator. I can't think of any better linkage mechanism or controlling cam arrangement that could improve on that.

[Sockmonkey]

I would want a cam for the displacer because the displacer is the mechanism used for delivering heat to power the engine and the heat input needs to be timed like the spark in an IC engine.

The displacer is designed to be very light so it can be easily moved carrying little momentum or inertia.

The displacer is not intended for transmuting any mechanical energy. It doesn't drive the engine or any load, so loses from friction are minimal.

None of these things are true for the piston. The piston transmits power, is relatively heavy, has momentum and inertia, sudden changes in motion and direction are detrimental, it transmits mechanical energy, anything that would interfere with it's smooth natural movement would tend to create a great deal of power loss and unnecessary friction and wear. There is no reason to interfere with it's movement and it has no, or God forbid, SHOULD have no "dwell" whatsoever, which is a complete stop. Why would anyone want the piston to remain motionless for any length of time?

Having the piston on a cam could produce no advantage whatsoever and could only be detrimental, as far as I can see.

Also, assuming it to be true, that some engines have been built with the power piston on a cam, the problem we are trying to remedy by putting the displacer on a cam, (lack of power, low torque) if successful, would introduce the same problems mentioned: cam wear, among other things.

I think the most efficient engine is a free piston engine driving a linear alternator. I can't think of any better linkage mechanism or controlling cam arrangement that could improve on that.

Not saying you should, I'm saying you could. I favor the linear alternator application myself, though solving the vibration issue usually means sticking two motors together to work in opposition.
Question: In a lamina flow engine, once you go past the orifice, does the tube have to be straight? I ask because curving the tube back around alongside the engine would let you butt two engines together to work in opposition without needing two burners.

[Tom Booth]

Interesting question.

A recently acquired supposition of mine, after watching some videos showing construction of laminar flow nozzles for attaching to garden hoses:

https://youtu.be/MOBcdnRQ4jY

This has me thinking the "regenerator" mesh, is actually a means of reducing turbulence, so that the piston is driven by a focused stream of air as it expands through the orifice. So, if true, between the orifice and piston should probably be straight. But inside or behind the mesh on the heating or regenerator side, I don't imagine it would matter, any more than it would matter to have a loop in a garden hose before the water went through a laminar flow nozzle.

That's all just conjecture, supposition, a shot in the dark, speculation. I think some experimentation on that front is in order.

[Tom Booth]

Anyway, actually seeing what laminar flow is and what it looks like from such water nozzle videos, gives some insight how a laminar flow Stirling works and why it can work without a flywheel.

The air/heat/kinetic energy flow is so narrow and focused there is a greater transfer of energy to the piston in relation to piston/engine diameter so that there is little excess heat to have to get rid of.

Something like hydrodynamic levitation.

https://youtu.be/mNHp8iyyIjo

[Sockmonkey]

Anyway, actually seeing what laminar flow is and what it looks like from such water nozzle videos, gives some insight how a laminar flow Stirling works and why it can work without a flywheel.

The air/heat/kinetic energy flow is so narrow and focused there is a greater transfer of energy to the piston in relation to piston/engine diameter so that there is little excess heat to have to get rid of.

Something like hydrodynamic levitation.

https://youtu.be/mNHp8iyyIjo

I suspect that laminar flow would only give useful amounts of boost if the engine is running at very high speeds due to air having little mass.

Here's an interesting little gadget.
https://en.wikipedia.org/wiki/Vortex_tube

Separates compressed air into hot and cold streams.
I know it's got my little brain wheels turning.

[Tom Booth]

I was intrigued with those vortex tubes years ago, even going so far as to build one myself.

It did work. Not great, but I did get noticably cold air out one side and hot (warmish rather) out the other.

Not a great way to create a temperature difference to run a Stirling engine though, as it takes a 15 amp shop compressor to make the compressed air to operate the vortex tube to create a very tiny localized temperature difference that maybe could run an LTD Stirling, that would not have the power to run more than an LED light, maybe.

[Tom Booth]

I suspect that laminar flow would only give useful amounts of boost if the engine is running at very high speeds due to air having little mass

I'm not so sure about that. The narrow orifice would increase velocity. Similar to hydrodynamic levitation. It doesn't work without a narrow orifice. But, of course, it's just a theory.

Laminar flow makes the stream through the nozzle that much more focused, like a laser compared with a flashlight, but who knows?

I'm not sure where the term "laminar flow Stirling" originated, but I assume there is some reason for it, providing a clue to how the engine works.

If the theory is correct, that provides some direction as far as possible improvements. Like steel wool is probably not that effective for reducing turbulence. Perhaps a bundle of narrow tubes, like the straws would give better performance. The distance between the "regenerator" and orifice, diameter of orifice, shape etc. Could have an influence on the laminar flow stream.

https://youtu.be/8I7EHb0XlJI

These same engines are also sometimes called "thermo-acoustic" but I don't think that is an original term and personally I find no evidence of these engines operating on any "acoustic" basis.

[Tom Booth]

There is a rather obscure and difficult to understand situation about gas and energy exchange that makes this laminar flow significant.

The energy of a gas is kinetic energy which is heat.

If a gas is "hot" and transfers heat to a surface the gas drops in temperature, but for a gas, velocity is also a measure of kinetic energy, so when a high velocity gas stream transfers energy to a piston, the gas also drops in temperature.

As a focused laminar flow can more effectively transfer kinetic energy to the piston, it also results in greater cooling. For a heat engine that means greater efficiency, or more heat converted to "work".

It is a strange idea that the heat added to a gas can not just cause motion in a piston, but actually BECOMES that motion, but apparently that is the case. The heat added to a heat engine that causes the engine to move, becomes that movement, and the "heat" disappears and the result is that in moving the piston, by whatever means, pressure or velocity, the gas looses heat.

[Tom Booth]

Another advantage of laminar flow, I think, is just that the kinetic force of the expanding gas molecules is highly organized and directed for maximal direct impact on the piston.

Ordinary expansion of a gas in a cylinder is pretty much completely random. Some molecules might be traveling towards the piston but others are traveling away and there may be all kinds of random collisions with each other and also with the cylinder walls. Like this: (please excuse the crude drawings)

IMG_20200625_204923743_resize_49.jpg (32.33 KiB) Viewed 5264 times

Laminar flow through an orifice, on the other hand is fully focused. All the molecules are aligned and moving in the same direction and are focused for maximum impact only on the piston and do not impact each other or the cylinder walls hardly at all.

As the piston is driven out, a high pressure stream is maintained to drive the piston while an actual partial vacuum is forming outside the focused stream.

As the heat energy becomes exhausted at the maximum throw of the piston, there is, I think, quite likely, an allready fully formed vacuum to begin pulling the piston back, even before, or without additional cooling due to heat transfer or conversion.

IMG_20200625_205001534_resize_76.jpg (62.57 KiB) Viewed 5264 times

[Tom Booth]

Also, a laminar flow continues with full force and impact, even after the energy or pressure that formed it is cut off.

So, does the expansion of gas in a laminar flow Stirling through the orifice continue to drive the piston out even as a vacuum is forming in the chamber behind it?

https://youtu.be/SKIescbcg9c

[Sockmonkey]

I was intrigued with those vortex tubes years ago, even going so far as to build one myself.

It did work. Not great, but I did get noticably cold air out one side and hot (warmish rather) out the other.

Not a great way to create a temperature difference to run a Stirling engine though, as it takes a 15 amp shop compressor to make the compressed air to operate the vortex tube to create a very tiny localized temperature difference that maybe could run an LTD Stirling, that would not have the power to run more than an LED light, maybe.

I'm thinking in terms of using it to improve the efficiency, rather than being the power source.