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Stephenz is correct

stephenz wrote: ↑Tue Jan 02, 2024 1:57 pm
...Alpha compression ratio > Beta compression ratio > Gamma compression ratio.

This shouldn't require math or geometry calcs to grasp, just the fact of total volume/swept volume. I often premise stuff with "everything else equal (always a dangerous premise)" since I'm unsure as to how many guys are on top of certain issues.

Tom has a valid point that displacer volume is not as 'dead' as we often think, but the typical convention remains of relating all none swept volumes as dead volumes.

The main reason alphas hover around 2:1 'compression' ratio is nothing more than common 90deg phasing. But one must exercise care when comparing volumes...

stephenz wrote: ↑Tue Jan 02, 2024 1:57 pm
- Alpha will ALWAYS [have] a Vmin much lower than Gamma/Beta, due to generally smaller dead volume and 2 pistons phased by 90 degrees providing a much lower combined V1+V2. Compression Ratio is the ratio of Vmax over Vmin.

The first sentence is correct, but the second sentence is wrong...the 'volume ratio' is Vmax/Vmin whereas the compression ratio is more elusive (no worries here).

I don't think it's a good idea to compare alphas to gammas & betas, since the displacer drastically changes everything. However, assuming alphas hover around 2:1 compression ratio, here's what a gamma would require to match this...consider ideal gamma with no dead volume except 100cc displacer volume and 100cc power piston volume. Allow displacer dwell whereby 100cc displacer volume maybe be in 100cc hot space or 100cc cold space. After power piston expansion, the displacer moves all remaining hot gas to cold space. Now, the power piston compresses 100cc of gas to displacer cold space effecting 2:1 compression ratio. In this scenario, the displacer dwell allows the volume ratio to equal the compression ratio.

stephenz wrote: ↑Tue Jan 02, 2024 1:57 pm
There is really no argument to have, Alpha's don't just win because of the greater swept volume. they win because they don't have the immense penalty of a displacer being technically a dead volume since its movement does not change pressure.

Lastly keep in mind that for any engine any of us can build, the ratio of swept volumes will always favor displacers over pistons. That Vd/Vp = 1.5 which you find online so often is one of rare rule of thumb that actually works for anyone wanting to build an engine with a heater temperature in the range of 300-500 C.

My biggest concern with gammas & betas is their larger regen requirement...I haven't been able to scheme a gamma with less than 1.35 the regen mass per similar alpha.

I could diagram a 10/1 or maybe even a 100/1 compression Beta, but it couldn’t run without a 20/1 or 200/1 temperature difference. So there’s really not much point. It seems idiots are idiots — higher indoctrination just reinforces the bastion.

Bumpkin

matt brown wrote: ↑Tue Jan 02, 2024 9:03 pm ...
My biggest concern with gammas & betas is their larger regen requirement...I haven't been able to scheme a gamma with less than 1.35 the regen mass per similar alpha.

If I were to actually attempt this build, it would likely not have any regenerator. At least nothing of a steel wool mesh with air. Of course piston/displacer and cylinder wall surfaces act as a regenerator to a degree.

However a regenerator works between a cold volume of air and a hot volume of air, theoretically at least, so would serve no purpose in this engine. No cold volume, no cold heat exchanger, no cold piston. No heat "rejection". No "excess" or "waste" heat to store or recycle in a regenerator.

I could diagram a 10/1 or maybe even a 100/1 compression Beta....

This is the main point, and the subject of Tom's MODIFIED Beta. Yes, the math proves an Alpha has a higher compression than a Beta given similar sized pistons. But the provided math does not exclude a modified Beta from higher compression ratios. This entire argument has been an exercise in gaslighting.

Bumpkin wrote: ↑Tue Jan 02, 2024 10:05 pm I could diagram a 10/1 or maybe even a 100/1 compression Beta, but it couldn’t run without a 20/1 or 200/1 temperature difference. So there’s really not much point. It seems idiots are idiots — higher indoctrination just reinforces the bastion.

Bumpkin

Is a certain engine configuration physically possible is one issue. Will it run is something else.

At the start I said simply:

Anyway, conjecture aside, I've been pondering what sort of design could be used to eliminate the cold side, and it just dawned on me a minute ago that a Beta type engine is the most like an IC engine.

On compression, both piston and displacer drive the air down to the heating chamber, then the expansion pushes the power piston out, and the displacer just kind of follows along.

The modification I'm thinking of is simply to take away the water jacket or cooling fins and instead line the power cylinder with some insulating material to retain heat.

I've avoided the Beta design generally because I don't especially like the idea of having to have a connecting rod pass through the power piston, however, if you want to eliminate the cold side and eliminate dead air space and achieve high compression, I'm not sure there is any better design.

Just have to nix the cooling and instead retain the heat for power output as much as possible.

The whole idea of "eliminating the cold side" is considered an impossibility by many from the outset, but I've "proven" to myself at least, through admittedly amateurish and flawed Micky Mouse experiments, that
it's possible, but regardless of any lingering uncertainties I'm forging ahead with an application, after only a little over a decade of thinking and debating and general procrastination and doubt

The whole concept is out in left field somewhere, so why harangue over the details?

Compression ratio without a cold side is a contradiction in terms to begin with right? So I don't know why those with a set bias against the whole concept are bludgeoning me over such minor details as compression ratios.

Further, that hastily written introduction is an oversimplification. Certainly eliminating the cold side will involve a bit more than simply taking away the cooling jacket from a conventional Beta.

If cooling is instead supposed to take place via high compression and adiabatic expansion then of course some means of generating high compression is required which means a higher compression ratio, which means some further modifications.

Exactly how much compression could be increased or how much might actually be necessary to effect "over expansion" as a cooling method is an open question.

I suspect it could be a quite modest, almost inconsequential modification.

In my experiments with the little LTD no more modification than a slight increase in the throw of the power piston was necessary to effect an apparent slightly below ambient self cooling or "heat pump" cooling effect.


https://youtu.be/P11q-BAhvqk?si=i2_MV_ra0kp1RqQD

Quickly?

That was my intention. Turned out to be not so quickly.

Tom, I would suggest that you paint any surface you measure matte black, to get a much more accurate reading of temperature. Also, since you now have a dc motor connected by belt, run the motor with a battery and see what temperature gradients you can get.

VincentG wrote: ↑Wed Jan 03, 2024 8:46 am Tom, I would suggest that you paint any surface you measure matte black, to get a much more accurate reading of temperature. Also, since you now have a dc motor connected by belt, run the motor with a battery and see what temperature gradients you can get.

This is a different engine than the sunnytech the motor is on, that I'm hoping to rebuild. But yeah, I do want to see the thermal consequences of an actual load on the engine.

I've been suggesting for years that it, theoretically, could possibly have a cooling effect due to additional heat being converted to work to power the external load, but have never directly tested that hypothesis experimentally. It has been reported in the literature or in patents but I don't know of any actual experiments, axcept indirectly, measuring pressure. A load certainly results in a steeper pressure drop at BDC, seems to make sense there is a concomitant temperature drop. But pressure is easier to measure.


https://youtu.be/dvomod6SsA0?si=wWtUd87Gwi3N54gH

But is that due to "work"? or simply lower RPM so increased heat transfer? Remains an open question I suppose. Would repeating the experiment with cold side insulated or made of acrylic still produce the same pressure/temperature drop?

But is that due to "work"? or simply lower RPM so increased heat transfer? Remains an open question I suppose.

Imo it's mostly lower RPM due to work. I don't think it's possible to compare steady state pv plots under varying loads without a variable lift displacer. Otherwise, you are not able to maintain RPM over varying loads while keeping the same input temperature.

Imagine running one engine like this...
400RPM, 600k input, 10% displacer lift, "x" amount of load(perhaps unloaded completely at this point)

Then...
400 RPM, 600k input, 50% displacer lift, "x" amount of load

Finally...
400RPM, 600k input, 100% displacer lift, "x" amount of load

Standard thinking would definitely suggest that cooling requirements will go up with longer heat input.

The only other valid test with a constant displacer lift would be to measure torque v. RPM with a dyno pull similar to ICE, where the engine is allowed to run up through the full RPM under a fixed load.

VincentG wrote: ↑Wed Jan 03, 2024 7:11 pm

But is that due to "work"? or simply lower RPM so increased heat transfer? Remains an open question I suppose.

Imo it's mostly lower RPM due to work. I don't think it's possible to compare steady state pv plots under varying loads without a variable lift displacer. Otherwise, you are not able to maintain RPM over varying loads while keeping the same input temperature.

Imagine running one engine like this...
400RPM, 600k input, 10% displacer lift, "x" amount of load(perhaps unloaded completely at this point)

Then...
400 RPM, 600k input, 50% displacer lift, "x" amount of load

Finally...
400RPM, 600k input, 100% displacer lift, "x" amount of load

Standard thinking would definitely suggest that cooling requirements will go up with longer heat input.

The only other valid test with a constant displacer lift would be to measure torque v. RPM with a dyno pull similar to ICE, where the engine is allowed to run up through the full RPM under a fixed load.

All good suggestions.

I was just thinking of measuring the cold plate temperature with a thermocouple.

I've already done dozens of tests with no apparent, or no measurable temperature increase above ambient.

Of course I'm told that is just because the cold heat exchanger is doing its job of rejecting heat. But my understanding is that to have a heat flow there needs to be a temperature difference between the cold plate and ambient. You can't just "reject" 80% of the heat input using 0-∆T.

Well, so they say the engines are so so inefficient the amount of heat being transfered that needs to be rejected is miniscule so barely detectable.

That is contrary to theory. Less efficient means MORE waste heat not less.

Why do so many people have such a hard time believing that a heat engine that is designed to convert heat into work actually does convert heat into work?

Anyway, if I'm getting a cold side hovering around ambient then adding an external load should reduce the temperature in an unambiguous way BELOW ambient.

I'm looking for a refrigerating effect, like a heat pump.

It most certainly seems to be there IMO.

So if the cold side is insulated with, say, a dewar (vacuum) like a thermos bottle or something. Under that a thermocouple probe or two or more and the temperature drops on the cold side instead of climbing and getting hotter, I don't see how that can be "invalid'.

Refrigerators don't work without insulation.

I've run engines for three hours on water at a steady boil and nowhere for the heat to go but up through the engine and hardly any detectable rise in temperature above ambient. IMO the "refrigeration" effect is plain and clear, from about 212°F down to 80°F or so sometimes barely above ambient and sometimes below ambient, if you can believe the infrared thermometer. Of course that's "invalid" for some reason.

Yes, slowing down the RPM can theoretically increase isothermal cooling, but not BELOW ambient or below the "cold reservoirs'. Unless the cooling is a result of something other than heat conduction to ambient.

You can't have heat flowing from colder to hotter, so if the cold side is below ambient something "anomalous" is going on, by conventional theory anyway.

It's just what should be expected IMO. From a heat pump or refrigerator.

matt brown wrote: ↑Tue Jan 02, 2024 9:03 pm Stephenz is correct

stephenz wrote: ↑Tue Jan 02, 2024 1:57 pm
...Alpha compression ratio > Beta compression ratio > Gamma compression ratio.

This shouldn't require math or geometry calcs to grasp, just the fact of total volume/swept volume. I often premise stuff with "everything else equal (always a dangerous premise)" since I'm unsure as to how many guys are on top of certain issues.

Tom has a valid point that displacer volume is not as 'dead' as we often think, but the typical convention remains of relating all none swept volumes as dead volumes.

....

Just curious, but who says?

Who says it is "convention" to relate "all none swept volumes as dead volumes.". ?

In an Alpha the crankcase is a non swept volume.

It seems to me some people have a strange idea about what "compression ratio" actually means.

stephenz (and others ?) seem to imagine that compression ratio "does not take into consideration anything but geometry/dimensions." and "compression ratio is a geometric figure.... It has nothing to do with gas whatsoever." and that solid metal objects within the engine should be included in calculating compression ratio.

Sorry, but the gas or air inside the power cylinder(s) is the subject of "compression ratio" the air is the substance being compressed.The air space in the cylinder is what is being reduced during compression. It is not different, it does not change "depending on what book or paper you're looking at."

It is simply the space (volume) occupied by the working fluid before compression (BDC) and after compression (TDC) expressed as a ratio.

It is a very very simple and straightforward concept it does not require "2-3 years thermodynamics" indoctrination to comprehend.

https://youtu.be/5qH_ThYLD6Q?si=Q4r8SAafCgsXvRmE

Kind of important in regard to this discussion is the deck height.

In an Alpha there is no time when both pistons reach TDC simultaneously

https://youtu.be/TV5cCFceAc4?si=71LYBv-BtpyDT__0

When one piston reaches the deck, the other piston is well below the deck and vice versa. This HUGE "dead air space" never goes away. I don't know how it is not obvious that this arrangement reduces the compression ratio dramatically.

Why compress and heat up a gas then allow it to expand? What advantage is there in that?

It takes just as much work to compress the gas as you can ever get back by letting it expand again right?

Well, IMO, or theory, it is a matter of converting useless random molecular motion (or "heat") all of which cancels out, into useful linear acceleration that can be harnessed to drive an engine and produce "work".

In the "thermoacoustic theory of operation" thread I recently posted this video, which I think demonstrates the point.

https://youtu.be/djyA_8Qv7pU?t=89

I think Freiburger would enjoy the fact he's in this thread lol.

I'm confused Tom, are you trying to recover the heat generated by compression? Or just use compression to boost efficiency?

VincentG wrote: ↑Mon Jan 15, 2024 1:05 pm I think Freiburger would enjoy the fact he's in this thread lol.

I'm confused Tom, are you trying to recover the heat generated by compression? Or just use compression to boost efficiency?

Well, historically, IC engines took off when compression was used, or increased. Not sure anyone ever knew why, it just worked.

As a means of simply "generating" heat, I don't think that would make much sense as any heat generated requires work. Temperature increases due to the same energy occupying a reduced volume.

One thing mentioned in the Motor Trend video is by adding the heat while the molecules are crammed closely together the energy can be handed off from one molecule to the next much more rapidly than when they are spread apart. The "mean free path" is greatly reduced resulting in a more forceful, explosive rapid expansion.

The name of the game IMO is conversion.

You aren't so much "recovering" or "generating" heat (or molecular motion) as just moving it to a position where it can be converted.

Hot air molecules in chaotic random motion cancel each other out and are useless, for conversion to "work" (or organized, directed motion) regardless of how "hot" it may be.

By compressing all the gas into the end of a closed cylinder, when the piston starts moving away, releasing the gas, ALL the gas molecules start moving in the same direction to fill the space.

Essentially the idea is to concentrate as much heat as possible from all available sources down into a small area. The gas then "wants" to expand. So you leave it just one escape route, one avenue. From that point, all it can do is expand by driving the piston and doing "work".

The whole idea that the engine is somehow intercepting a "flow" of "heat" traveling from a "hot" to a "cold" reservoir, is a theoretical model that has produced virtually no improvement in these engines in 200 years.