Displacer 90° out of phase why?

[Tom Booth]

Again. There is no heat in adiabatic compression.

You, as usual, don't know what you're talking about or are so fixated on WORDS you would argue a "German shepherd" is not a "dog" and neither are "canine"

adiabatic does not mean there is no "heat" or no possibility of generating heat by compression. It just means no energy crosses the system boundary in the form of heat. Adiabatic compression most certainly does create "heat" or an elevation in temperature, as is well known. In diesel engines and fire pistons for example.

Please stay off my threads if you don't mind. I'm so sick and tired of your ridiculous, petty argumentative and nonsensical troll posting.

You are only taking the work energy and storing it as internal energy, during a single stroke. Loss of work energy, stored as internal energy, indicated by temperature.

Yes, indicated by a rise in temperature. Raising the temperature of a gas causes EXPANSION of the gas. Expansion of the cas does WORK driving the engine.

Less work to output.

It seems you have about as much comprehension of engine operation as you have about refrigeration.

Completely clueless

Please stop disrupting my discussions with your interminable BS

No free lunch. No heat/no energy to output as work.

If you have cooling for half the stroke you will have used less work for compression, thus have more to output for the cycle. Of course, that is the Carnot Cycle.

PV diagram needed.

You are certainly living up to your name.

Please go away.

[Fool]

Sheesh, what a winer.

[Jack]

https://scholar.lib.vt.edu/ejournals/JO ... oster.html

With this engine they find the most optimal angle is 125 degrees.

[Tom Booth]

https://scholar.lib.vt.edu/ejournals/JO ... oster.html

With this engine they find the most optimal angle is 125 degrees.

Interesting.

I'm not sure how significant it is though. That engine is unusual in a number of ways. It has a rotary displacer as well as "ports".

Compress_20240613_121111_1976.jpg (36.67 KiB) Viewed 2191 times

Recall that the stepped profile of the segments exists for about 180° only (see Figure 3). Hot and cold ports connect to the power cylinder through passageways. The cold port and its passageway represent a heat sink in that they are kept cold by the engine’s liquid cooling system. These areas are also insulated from the hot workspace. The hot port and its passageway represent thermal energy input, being in communication with the hot workspace. When the displacer rotates through its cycle, it alternately blocks and opens the hot and cold ports.

I think the 90° phase "resonance" would have to do with the moment of actual heat input. From my scanning through the article so far, it isn't clear to me how this engine actually introduces heat, but I kind of suspect the opening and closing of "ports" and the necessity for passing the working fluid through various passageways between the actual "thermal energy input" and "hot working space" causes some disparity or delay between displacer position and actual heat input.

Hard to say if this actually contradicts or confirms the theory.

[Tom Booth]

Looking at what I assume would be the valve or port opening or uncovering mechanism on one of the displacer segments, this appears to be offset.

That is the open ports would not be directly 180° opposite to each other but actually offset by the width of the port opening.

Compress_20240613_131742_2807.jpg (21.08 KiB) Viewed 2187 times

Again, I'm not entirely sure how heat is actually introduced. But the port "cover", I assume to be the side of the displacer would not be fully open or closed a direct 180° opposite displacer rotation apparently.

[VincentG]

And I thought 90 degrees was bad enough...

[Tom Booth]

And I thought 90 degrees was bad enough...

I think maximum pressure would still develop near TDC.

A "spring system", if it is recognized that gas has compressibility or a certain "spring" quality, a spring needs to be "loaded".

Similar to a sling shot or a bow (as in bow and arrow). The elastic needs to be loaded before it becomes an effective source of propelling force.

So, if the working fluid is elastic in such a way then before it can effectively propel the piston it would need to be compressed or "loaded".

The force would still be released around TDC but the "loading" would begin 90° in advance when the compressive force is greatest, while the piston is traveling at its highest velocity to "pull back the bow" so to speak.

[VincentG]

The spring analogy is bunk. An engine is not a spring bouncing back and forth, it's more like canon being loaded time after time. An adiabatic bounce looks impressive, but it won't pull a trailer up a mountain.

[Tom Booth]

The spring analogy is bunk. An engine is not a spring bouncing back and forth, it's more like canon being loaded time after time. An adiabatic bounce looks impressive, but it won't pull a trailer up a mountain.

You do have to add heat as well.

I view it as like a baseball bat (added heat) meeting a pitched baseball (atmospheric "compression") the two forces meet and combine to propel the ball or piston.

Makes perfect sense to me.

[Tom Booth]

In other words, it's not just an "adiabatic bounce" or oscillation, it's a damped, "forced" or "driven" oscillation.

The damping is the friction and the load, the trailer that needs to be pulled. The driving force is the added heat.

I think this helps to explain why Stirling engines are so incredibly inherently efficient because all the energy "lost" or "negative work" during compression is utilized to "load the spring" or "pull back the bow" or sling shot and so recovered and utilized for expansion during the power stroke.

[Tom Booth]

As far as the engine in question, It is usually considered a characteristic of a Stirling engine that it has no valves. The valves introduce an added element of restraint and control over the movement of the working fluid.

In other words, the working fluid is not free to oscillate at its natural frequency but has no choice but to wait on the opening of a port.

Technically, I think some would argue it is not actually a Stirling engine in the traditional sense.

I still don't really know for sure the exact means by which the ports are open, the side of the displacer I pointed out previously in the other photo of the engine's internals does not appear to fully close the port but only covers half, so I don't know, there may be something else.

Perhaps it might be possible to increase that engines performance by adjusting the port location to ensure the heat input valve is fully open at the 90° advance point.

[Tom Booth]

If we relate this to a bow and arrow.

There are two forces involved.

Compress_20240613_220659_9821.jpg (16.21 KiB) Viewed 2139 times

Image source: https://legendarchery.com/blogs/archery ... ery-part-1

The mans right arm is pulling back on the bow string. The left arm is exerting force or resistance in the opposite direction.

I would liken the right arm pulling back to the force of compression. The left arm offering resistance or pressure in the opposite direction is like the expansion from heat addition.

The bow string in the relaxed state is the midway 90° point where both compression and resistance start.

The piston, of course, would be analogous to the arrow, to which both forces combined are ultimately applied (at about TDC).

It might be hard to imagine or conceptualize just how two forces apparently directly opposed to each other and exerting pressure in opposite directions don't just cancel each other out rather than combining to convert potential energy into kinetic energy, but that is the nature of an oscillating spring type system.

Actually, I guess you could say they do cancel each other out. Until released.

[Jack]

Looking at what I assume would be the valve or port opening or uncovering mechanism on one of the displacer segments, this appears to be offset.

That is the open ports would not be directly 180° opposite to each other but actually offset by the width of the port opening.

Compress_20240613_131742_2807.jpg

Again, I'm not entirely sure how heat is actually introduced. But the port "cover", I assume to be the side of the displacer would not be fully open or closed a direct 180° opposite displacer rotation apparently.

I once found a more detailed file with drawing for this engine. I'll try to look it up when I'm home again.
But if I remember correctly the ports do slightly overlap, which helps "clean" the piston of either hot or cold air.

In the test setup heat is introduced by a burner covering one half of the displacer body.

[Tom Booth]

...
I once found a more detailed file with drawing for this engine. I'll try to look it up when I'm home again.
But if I remember correctly the ports do slightly overlap, which helps "clean" the piston of either hot or cold air.
....

That would be good, thanks.

If it turns out there is something to this 90° driven oscillation theoretical connection, it would answer a question that's been puzzling and frustrating me for as long as I've known about the "traditional" 90° displacer offset "RULE".

As far as I've ever known it was arrived at purely by trial and error. It "just works" but I've never seen any explanation why.

I've said for a long time now that a Stirling engine LOOKS LIKE a resonating spring type apparatus rather than the classic flow through Carnot water wheel analogy, but the 90° resonance thing really clinches it in my mind. Mystery solved.

So why it doesn't appear to work or be applicable to this engine is a good question.

[Jack]

I had a sudden moment of clarity hehe, found the extra info.



https://patents.google.com/patent/US20110061378

They aren't so much drawings but very detailed pictures of the build-up.
Hope this helps.