Displacer hot space vs cold space study

[matt brown]

Review this post and mine just prior.

viewtopic.php?f=1&t=5543&start=15#p20013

This is the idealized gamma I meant and what you and Vincent were talking about in past regarding dwell via magnets or whatever means. I thought it was odd that you'd write of dwell so easily, so I thought I'd explore what effects it might provide (and glad I did).

[matt brown]

My deep dive on gammas is loaded with various parametric studies, but this cold space vs hot space stuff is a standout. All my stuff is via legacy techniques that Ericsson would recognize, no computer sims, online gas calculator, etc. Yep, that means it's slow, but this time gives me a better feel for stuff as it evolves (or devolves). This particular study evolved thru this sequence:

(1) 6v DPcyl with 6v swept vol and 3v PPcyl with 3v swept vol
(2) same except for DPcyl with 3v swept vol...UPPER 3v
(3) same except for DPcyl with 3v swept vol...LOWER 3v
(4) same except for PPcyl with 6v and 6v swept vol (aka, I doubled orig. PPcyl vol)
(5) same except for PPcyl with 1.5v and 1.5v swept vol (aka, I halved orig. PPcyl vol)

It's all about selectively gaming similarity, and I know one very sharp physicist (hey Bumpkin, remember Lee White) who thought this was total BS, especially after Allan Organ released Air Engines with a crazy $160 price (I was gifted a copy upon release). But, I'm more open minded than a physicist, so I can doodle away without getting all bummed out.

I later decided to add a crude "cold hole" to this study via massive increase in PPcyl vol with full sweep, but nothing amusing came of it (sorry Tesla fanboys). Then, just to round this group out, I decided to add a "hot hole" via massive increase in DPcyl hot space, and hit the jackpot !!! After a few days rest, I recalibrated my PVTm values to chase what became the OP graphic in this thread. The trick was choosing start values that would carry thru without any goofy decimals (no offense Goofy). This took nearly a week of chasing in circles, but I finally got it in a tidy set of values.

[Tom Booth]

Review this post and mine just prior.

viewtopic.php?f=1&t=5543&start=15#p20013

This is the idealized gamma I meant and what you and Vincent were talking about in past regarding dwell via magnets or whatever means. I thought it was odd that you'd write of dwell so easily, so I thought I'd explore what effects it might provide (and glad I did).

What I was saying there that I would say is mechanically impossible is to have the PP "wait at TDC".

What Vincent and I were discussing was displacer "Dwell".

A displacer is practically weightless and isn't driving the engine and could be, and sometimes is completely decoupled from the crankshaft. (Ringbom, magnetic etc.) So giving the displacer more "dwell" or wait time is not an issue.

Having the power piston stop and wait ?

But that was not my main objection. You might be able to engineer a power piston with dwell, using a cam system but supplying heat all the way to BDC leaves the cylinder full of hot air so the piston would not be able to return.

Unless you agree that all the heat input could be converted to external work output resulting in a pressure drop/vacuum, but you are arguing against that elsewhere. Or so it would seem. Right?

[matt brown]

What I was saying there that I would say is mechanically impossible is to have the PP "wait at TDC".

What Vincent and I were discussing was displacer "Dwell".

A displacer is practically weightless and isn't driving the engine and could be, and sometimes is completely decoupled from the crankshaft. (Ringbom, magnetic etc.) So giving the displacer more "dwell" or wait time is not an issue.

Having the power piston stop and wait ?

I agree, far easier and straight forward to achieve DP dwell than PP dwell. Martini tried reversing ringbom scheme where DP was mechanical while PP was FP, but I don't think this ever worked out (likely as you say due to driving vs driven). However, there's more than one way to skin a cat...

But that was not my main objection. You might be able to engineer a power piston with dwell, using a cam system but supplying heat all the way to BDC leaves the cylinder full of hot air so the piston would not be able to return.

Unless you agree that all the heat input could be converted to external work output resulting in a pressure drop/vacuum, but you are arguing against that elsewhere. Or so it would seem. Right?

This is where you losing me...an ideal gamma only produces power on the cold side of cycle vs an unideal gamma produces power on both. I'm chasing the best, undeterred by current crop of SE.

[matt brown]

Matt, I'm a bit confused here. Something I've been harping on from time to time is to consider the "neutral" state of a Stirling engine. I would consider graphic B4 to be the neutral state(3 bar, displacer and power piston in middle position). It seems you are counting the power piston volume as cold space here, but I'm not so sure this is accurate.

Except for the temperature gradient in the regenerator, an ideal gamma only has 2 temperatures: (1) a hot space, and (2) a cold space. If the PPcyl vol isn't cold space, what would it be ???

Graphic A2 shows the peak pressure state the engine will see as 6 bar.

Conversely, A4 shows the minimum pressure state the engine will see as 2 bar, where one might expect less.

Cycle A has 3:1 (extreme) P swing vs cycle B has 2:1 (extreme) P swing. Note, both A and B are "square" cycles where P after compression (stg 1) is the same as P after expansion (stg 3). As for 2 bar in A4, why should one expect less ?

I think it would be more realistic to count the power piston volume as half hot space and half cold space at graphic B4.

Huh...the volume is one thing, but there's also the gas mass "m" to consider.

But then to my way of thinking, a balanced Stirling engine with 3 bar at position B4 will only reach 5.62 bar at position A2. Thats 3 bar x 1.25(pp back to TDC) x 1.5(from B4 neutral state of 450k to 600k)= 5.62bar.

You'll have to unpack this a bit more for me (especially the B4 vs A2 part).