Displacer 90° out of phase why?

[Jack]

I don't understand how you get to the conclusions about the timing. I've been over the patent again and have a different understanding of it.

I just want to clarify that I'm not trying to prove anything here. I'm merely trying to provide more data to study your theory and am discussing the way to interpret this data.
At the moment it seems you think I'm looking at it wrongly and I think the opposite.
It's not clear to me yet who is misunderstanding this engine, it could be either of us.

[Tom Booth]

The article you posted concluded:

Summary of Findings Regarding the Ideal Phase Angle

The SWATT engine is a Stirling, however, it functions best with a phase angle that is significantly different from other Stirling engine configurations. It is not possible, at this time, to speculate as to why. What can be said is the ideal phase angle for SWATT is near 125°

Nothing more to say about it.

I disagree with calling it a Stirling. It's crap.

Admittedly this engine is, for whatever reason "different".

I've already gone over several reasons why that engine is irrelevant to this discussion.

I'm interested in why a normal standard Stirling engine performs best at a 90° advance and if that has something to do with the 90° offset of other damped driven oscillators.

That engine is not any kind of normal standard Stirling engine. In my opinion it's a total piece of junk. It throws half the heat away to the liquid coolant, the timing is basically completely backwards. IMO who ever designed it had no idea what they were doing. Personally I've never seen such a horrendous example of shoddy engineering. It's a wonder the thing could be gotten running at all.

[Jack]

Fair enough, you're entitled to that opinion.
I have nothing invested in this, was just trying to show some other info.
I don't think I understand piston engines and especially Stirling engines enough. It's still feels like crude old tech to me.

[Tom Booth]

Fair enough, you're entitled to that opinion.
I have nothing invested in this, was just trying to show some other info.
I don't think I understand piston engines and especially Stirling engines enough. It's still feels like crude old tech to me.

Aside from anything else, "resonance" is usually defined by the relationship in the STILL position.

Two pendulums for example. At the end of the swing while changing direction the pendulum is motionless.

If they swing together they are in phase, if the still positions are 90° apart, one in the center moving at high velocity and the other at the end of its swing they are "in resonance".

Same with reciprocating piston and displacer. The 90° offset is from the motionless positions.

When is a rotary displacer motionless? It never is.

IMO an alternative would be to relate it to the start of heat input as that is where most Stirling engine displacers would be motionless. Just before the displacer rises to let in heat.

But they "guessed" opposite and put the 90° offset 180° from where I would have thought it should be.

Their heat input is "retarded" 90° rather than "advanced" 90°

They did not incorporate any means for adjusting the timing the full 180° that would be necessary to achieve "resonance".

Their 90° offset is 90° AFTER the piston is at TDC when it should be 90° BEFORE TDC.

Apparently they are academics doing academic research or something and don't know the difference, I don't know, but an engine can run with the timing retarded. Not with much power and not "at resonance".

The valve port placement and timing for that engine does not permit heat input until well after TDC.

If the engine showed some extraordinary performance or power output or something it might be worth looking deeper into it, but I don't see any point in wasting a lot of time trying to figure out why their off timing dog of an engine won't run right.

There are so many things wrong with that engine, IMO, it's like trying to figure out why a plane crashed with no black box recorder. Who knows why that engine is "different". Even they don't venture a guess.

Well, I see a number of reasons. It's a rotary not reciprocating displacer timing is reversed by 180°. Heat input is screwy due to port location, to name a few.

[Jack]

You might be right, you might not be. It's your theory and I have no opinion about that.
I just think we can do better than a pulsating/resonating engine. I think we can make an engine that produces peak power all the time in stead of half or less.

But that might not be a discussion for this topic. I'll leave it out of this.

As you were haha

[Tom Booth]

You might be right, you might not be. It's your theory and I have no opinion about that.
I just think we can do better than a pulsating/resonating engine. I think we can make an engine that produces peak power all the time in stead of half or less.

But that might not be a discussion for this topic. I'll leave it out of this.

As you were haha

Generally speaking, precision timing is pretty crucial for all engines of any kind. No engine is going to run without proper timing of the ignition / heat input. Turbines are an exception.

The 90° offset on a Stirling engine never made sense to me, thinking in terms of an IC ignition engine. So I've done all kinds of things to try to make "improvements" but without being able to claim any real success.

I think the resonance of a "driven oscillator" in spring type systems provides a satisfying explanation and could help guide the design of better more efficient and powerful engines once understood.

Most research (including me previously) seems to be working against the 90° thing trying to change it rather than understand and working with it.

[Fool]

In engineering and physics, there is a tool called a free body diagram. It is a drawing of a single part of a machine with force arrows, vectors, added for how it interacts with the other parts of the machine. Vectors are the tools to add up forces in all three directions.

For example: a block on an inclined plane, a ramp. The block is drawn with a vertical downward pointing arrow representing gravity, labeled Mg. It has a normal force perpendicular to the bottom of the block pointing upward, and a parallel friction force arrow pointing up hill. From that, all the forces should add to zero, vectorially. That means the item is static, not accelerating.

The following link may be of interest:

https://en.m.wikipedia.org/wiki/Free_bo ... am#/search

Tom's bow and arrow would be reduced to a bow with a force pointing forward and two diagonally down to the point where fingers are holding the string. This would be static if held in a drawn position. All three forces would add up to zero. The bow is not moving.

When released the forces add up to Ma mass times acceleration. Dynamics in addition to statics. It would be the mass and acceleration of the arrow. The forces on the bow would remain until the bow's bend began relaxing. The pull back force would be replaced by acceleration of the arrow. For dynamics one of the forces is replaced by a mass accelerating. Equal and opposite reactions.

The same happens inside an engine. The pressure acts against an accelerating piston. No piston mass acceleration, no pressure.

[Tom Booth]

In engineering and physics, there is a tool called a free body diagram. It is a drawing of a single part of a machine with force arrows, vectors, added for how it interacts with the other parts of the machine. Vectors are the tools to add up forces in all three directions.

For example: a block on an inclined plane, a ramp. The block is drawn with a vertical downward pointing arrow representing gravity, labeled Mg. It has a normal force perpendicular to the bottom of the block pointing upward, and a parallel friction force arrow pointing up hill. From that, all the forces should add to zero, vectorially. That means the item is static, not accelerating.

The following link may be of interest:

https://en.m.wikipedia.org/wiki/Free_bo ... am#/search

Tom's bow and arrow would be reduced to a bow with a force pointing forward and two diagonally down to the point where fingers are holding the string. This would be static if held in a drawn position. All three forces would add up to zero. The bow is not moving.

When released the forces add up to Ma mass times acceleration. Dynamics in addition to statics. It would be the mass and acceleration of the arrow. The forces on the bow would remain until the bow's bend began relaxing. The pull back force would be replaced by acceleration of the arrow. For dynamics one of the forces is replaced by a mass accelerating. Equal and opposite reactions.

The same happens inside an engine. The pressure acts against an accelerating piston. No piston mass acceleration, no pressure.

I couldn't have said it better if I cut up all the words in a physics book and put them in a box and shook it up and dumped it out on the table.

[Fool]

Thanks.

[Tom Booth]

Thanks.

Your welcome.

But IMO you are just unduly complicating matters.

An oscillating spring system is essentially just an interplay between potential energy and kinetic energy. I chose a very simple, easy to understand illustration that depicts that.

Compress_20240613_220659_9821.jpg (16.21 KiB) Viewed 1561 times

Who knows what if any point you are trying to make, just some vague jab with a bunch of irrelevancies to confuse or refute something you pretty obviously don't understand.

A compressed spring or drawn bow represents potential energy. Released that potential energy becomes kinetic.

Simple as well as factual.

[Fool]

How come the bow, being pushed forward by the arm, doesn't fly forward with the arrow?

[Tom Booth]

How come the bow, being pushed forward by the arm, doesn't fly forward with the arrow?

It's fixed in position by being gripped tightly at the hand grip obviously.

What's your point?

[Fool]

It has nothing to do with grip. It is force and reaction balance. The arrow being accelerated forward has the equal and opposite reaction of pushing the bow backwards. The arm only has to resist a backwards push for the entire stroke. Then zero motion or force, except for gravity pulling the bow downwards.

This is easily proven by not gripping the bow as the arrow accelerates. The kickback and force holding it drawn are the same and doesn't stop until the arrow leaves the string.

This is easier to understand with free body diagrams. And vector addition.

The really cool thing about bows, and ballistas, is that the momentum of the moving/flexing bow, gets transfered to the acceleration of the arrow, so that the bow comes to a screeching halt just before the arrow leaves the string. This makes the bow more efficient than a catapult or slingshot where the arm or patch keeps moving forward after the mass leaves the pocket.

This is a result of the bow string vectors changing, all the way to vertical at the end of the throw. And why the bow pushes backwards until the arrow leaves the string, with the bow and string motionless.

[Tom Booth]

It has nothing to do with grip.

The point is it is held in a fixed position at arms length. Some people use a wrist strap so the bow doesn't jump out of their hand and so they don't have to grip it tightly for better control.

...

This is easily proven by not gripping the bow as the arrow accelerates.

Good luck with that.

Anyway I don't see the relevance.

Are you trying to deny that potential energy is converted into kinetic energy,? Because that's what it sounds like.

How does your long drawn out lesson in bow and arrow dynamics relate to the topic? Just another off topic derail into mostly incoherent rambling on a topic you know nothing about.

[Fool]

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.

You brought up the "long drawn out lesson in bow and arrow dynamics". I was merely adding the standard engineering tools to help in your "guessing".

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

My points is the draw force is replaced by the acceleration reaction, and the two still cancel.

"Are you trying to deny that potential energy is converted into kinetic energy,? Because that's what it sounds like."

I was explaining how force cancelation is replaced by mass times acceleration and force cancelation, as a means of converting spring potential energy into arrow kinetic energy.

Thought it would help in your analysis of how a pressure cylinder and piston might be analyzed. Since you were obviously having difficulty doing so.

Free body diagram of a cylinder. Forces:
1, Mass of cylinder times gravity pointing down wards.

2, Pressure times area pointing left towards the head.

3, Normal force from ground or frame pointing up.

4, Horizontal force from frame or ground, pointing opposite to the pressure force, to the right, and towards the piston.

5, Normal force from piston mass times gravity pointing downwards at the position of the piston.

These all balance because the cylinder doesn't move or accelerate.

Free body diagram of the piston. Forces:

1, Pressure force pointing to the right from the internal gas.

2, Mass of piston times gravity pointing downward.

3, Normal force pointing upwards from cylinder.

4, Pressure force pointing to the left toward the head from the outside atmosphere.

The up and down forces all cancel, because the piston isn't moving up and down. The left and right forces may or may not cancel. If they don't cancel, it results in the following opposing reaction:

5, Mass times acceleration of piston, in the direction of the residual force.

There is no 'drawing of the string' equivalence in a running engine. There can be, but, that would be a wasted form of over expansion and or over compression, and would suffer from hysteresis. There could also be an external force, such as initial flywheel push. The internal forces are caused by internal energy pressure differences from thermal energy input or rejection, also known as heat, and volume changes. Pressure differential and momentum interact to produce volume changes. Heat and string-draw are not the same thing, other than being totally different kinds of energy.

Gave you the chance to discover it for yourself. Sorry I had to be more detailed.

Free body diagrams are very useful for Stirling Engines, and many others engineering studies. I was offering the process to those that care.