Displacer 90° out of phase why?

[Jack]

I used to think it had something to do with the regenerator. My thought was that it works as a timing enhancer. It basically starts heating and cooling the fluid sooner in the cycle.

But I never had the chance to experiment with that yet. Just a thought experiment.

[Tom Booth]

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.

Looks like a complete disaster to me.

First of all it appears they have the piston advanced 125° ahead of the displacer.

The displacer is supposed to be advanced ahead of the piston.

When the hot port opens and cold port closes the hot and cold regions are nearly evenly exposed.

The whole thing looks like just a nightmare of off timing and inefficiency.

So it looks as though the hot port doesn't open until the power piston is already 1/3rd or so past TDC.

So the hot port will still be open at BDC all the way through 1/3rd of the way into the compression stroke.

That's how it looks to me.

The whole thing is just a mess is how it looks to me.

But that's kind of the problem with rotary displacers anyway, but this thing just seems to really just be fighting itself a lot of the time.

[Tom Booth]

If it were possible, going only by the drawing provided, to have a 90° advance "at resonance" with the begining of heat input (start of the hot port opening) the power piston crankshaft would need to be attached where I've indicated by a green dot.

Compress_20240615_004830_0717.jpg (24.77 KiB) Viewed 1334 times

The location of the ports themselves though, also should be changed.

The original location shown would have the gas being heated for 1/4 revolution but unable to go anywhere because the port is closed and will remain closed for another 1/4 revolution.

Logically the hot port should be opening at the same time that the working fluid begins moving into the heated zone.

So the ports would need to be relocated to the locations where I've placed the Red (hot) and blue(cold) dots:

Compress_20240615_010055_5378.jpg (25.09 KiB) Viewed 1334 times

As it was, the port locations and timing adjustment allowance range completely ruled out any possibility of the engine achieving an "in resonance" effect.

Now possibly the drawing is not complete or I'm misinterpreting something, but just going by what I can see, that is my assessment.

The original timing is almost 180° out of time so the allowed range of timing adjustments don't even include the point where there could be "resonance" and even then the heat input does not coincide with the opening of the hot port.

[Tom Booth]

With the ports relocated, the power piston connecting rod would have to be relocated to where I've added an orange dot:

Compress_20240615_013230_0109.jpg (25.2 KiB) Viewed 1331 times

So as the hot port begins to open, and heat is starting to be introduced, the power piston would be "in resonance" 90° BTDC.

[Jack]

I don't know if that drawing is true to timing and all. Or just a schematic.
I think you should read the whole thing in the link with all the pictures.
It's just a bit unfortunate that there aren't any output figures except rpm.

[Tom Booth]

This figure 5 and the description in the text of the patent appears to coincide with the previous diagram exactly.

Compress_20240615_020204_4109.jpg (136.75 KiB) Viewed 1324 times

The text for that figure also reads:

The rotary valves are
positioned such that the hot valve is completely closed and the
cold valve is completely open for about another 90 degrees of
clockwise rotation.

So my interpretation seems right.

The hot gas is basically trapped behind a closed valve through the first 90° of rotation after the heating of the working fluid begins.

I might have once considered that a positive thing, to provide a blast of hot air all at once but the timing even for that is off and such a restricted flow would certainly interfere with any "natural resonance".

[Jack]

I don't know. They're ports, not valves, and it's still a fully open system. So the piston is always open to the displacer, the side just changes. This creates a flow direction, that's all.

The open port side changes when the displacer is half way between the hot and cold side.

[Tom Booth]

I don't know. They're ports, not valves, and it's still a fully open system. So the piston is always open to the displacer, ...

Well, I can only go by the patent description and my own experience with "ports" that are either open or closed by being covered by some moving or sliding part that opens and closes the port. Two cycle engines for example use ports, but such ports serve the same purpose as a valve.

The actual patent text quoted above describes them as "rotary valves"

The rotary valves are
positioned such that the hot valve is completely closed and the
cold valve is completely open for about another 90 degrees of
clockwise rotation.

And throughout the text of the patent they are described rather consistently as "valves".

A "port" is, in most engines where they are used, just a type of valve, either "completely closed" or "completely open" as described (underlined) in the quoted passage above.

You say the ports are "fully open" but the patent says "rotary valves" that are either "completely open" or "completely closed".

One or the other has to be wrong I would say. Either your description or the patent description. I'm afraid in this instance I'll have to favor the patent description and my own experience with engine ports and valves.

Sorry about that. I don't want to get into a debate about it. The patent photos, drawings and descriptions seem perfectly clear and unambiguous. The ports are "rotory valves" that are either "completely open" or "completely closed".

[Tom Booth]

Anyway, IMO, that is a kind of hot air or gas engine, but cannot, or should not be classified as a "Stirling" engine.

The presence of these long conduits and ports along with the reversal in the interpretation of 90° offset putting the piston 90° ahead of the displacer rather than the other way around renders "resonance" not just unlikely but actually impossible. A 90° resonance is completely outside the mechanical constraints of the engine.

[Jack]

Ok the ports or valves don't really matter. What I was getting at was that it doesn't matter as one of them is open at all times and there's nothing else stopping flow. So the power piston is always open to the displacer. Either with the hot or the cold port/valve. So I think it still is a Stirling engine. The ports/valves just determine a certain flow direction and are there to keep the design practical. They stop nothing but a flow direction.

That's how I see it at least.

[Jack]

In essence it's still the same thing. It shuttles around air from a hot to a cold side to power a piston. At any and all times during the cycle there's a full port/valve/conduit/opening to the power piston. It just changes sides. They had to do this because it's a rotary displacer, how else do you keep that connection open at all times?
I don't think you should draw any conclusions about the timing from the drawing/schematic I posted. More from the writing that accompanies it.

[Tom Booth]

Resonance has to do with the driving force. In a heat engine that would be expansion from heat input.

Page 4 of the downloadable patent PDF text makes perfectly clear that the rotary valves are either fully open or fully closed, except for a brief instant when they are both open.

That whole contraption is 100% outside the range of applicability for any kind of 90° driven resonance as discussed here.

You are of course free to think or conclude whatever you want, but IMO that thing is far far outside the realm of consideration for this theory. Interfering with the heat flow, forcing the timing with physical valves etc. is enough, but that engine configuration makes a driven spring system resonance actually impossible. The range of timing for heat input is 180° off. Completely opposite to a Stirling engine. The range of adjustment makes achieving resonance as under consideration here, physically impossible for that engine without MAJOR modifications. Probably the whole thing would have to be rebuilt from scratch.

A much simpler rotary displacer Stirling version could probably be made out of tin cans if someone wanted to experiment further

[Jack]

Rotary Valve Mechanism
Another design feature that is possible because of the rotary displacer is a rotary valve integral with the first displacer segment and the adjacent portion of the housing. This arrangement does not add additional moving parts, but it effectively directs the working fluid in the following way. The power cylinder has two ports, one in communication with the hot workspace through the hot port (see Figure 6) and one in communication with the cold workspace through the cold port. The cold port is not visible in Figure 6; it is obscured by the segment. Regardless, it is situated 180° from the hot port and lies on the same circular centerline in the side of the displacer housing. These ports are positioned immediately adjacent to the stepped profile groove occupied by the first displacer segment. 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. During isovolumetric heating (expansion), therefore, the hot working fluid is inhibited from moving through the cold passageway, even though pressure throughout the engine is the same. Similarly, during isovolumetric cooling (compression), the cold working fluid is inhibited from moving through the hot passageway.

So it's just a way of directing the airflow. There's no other limitation and it's not actually closing off the power piston completely at any time. Also the ports/valves are at exactly 180 degrees and the displacer discs are formed at exactly that as well. I don't know where you got the information that both ports are fully open together at one point, to me they overlap a bit but not both fully open. Even if they did, I don't think it would matter much as there's an open passage to the power piston at all times.

And for the phase angle, my opinion is that you're still fixed on the drawing I quoted. In the article they explain how they tested the 90 degree angle because that's what the literature states and how they found the 125 degree angle more efficient.

[Tom Booth]

Even supposing the working fluid (that is just begining to be heated maybe 35° BTDC it looks like, already past 90° "resonance" position) can travel up the open cold port/transfer tube, the engine is water cooled. The cold transfer tube is undoubtedly cold, I think it safe to assume, the hot valve/port/transfer tube doesn't open, isn't available until the piston is about 45° PAST TDC.

How much heat could be transfered to effectively influence anything before the hot port opens is questionable, but AT BEST, heat input can't begin at all until the piston is already past the "ideal" point of resonant response

At best it's about 50° off and in actuality it's more like 140° off.

As far as I can see, it is just not even possible at all to actually test how this engine would respond with a 90° advance because it is mechanically constrained to be 90° retarded and physically cannot be adjusted far enough in either direction to be set with a 90° advance.

The cold port and its passageway represent a heat sink in that they are kept cold by the engine’s liquid cooling system

I really don't know what your trying to prove with this but one oddball patent with so many probable issues does not nullify or invalidate the decades or even centuries the traditional 90° offset has been used and sworn by by many, in millions upon millions of Stirling engines.

I think I've given this one oddball so-called "Stirling" engine patent way more time and consideration than it deserves.

[Tom Booth]

...
And for the phase angle, my opinion is that you're still fixed on the drawing I quoted. In the article they explain how they tested the 90 degree angle because that's what the literature states and how they found the 125 degree angle more efficient.

Sorry to say but it appears these researchers did not understand what was meant by the 90° offset and tested using a 90° retarded rather than advanced setting as their starting position.

That is a full 180° out of time. Away from the "resonant" position.

I'm not going by your drawing, I've been over the entire patent.