Modified "Hot" Beta engine

[Tom Booth]

...
...There is nothing in it for me here, I'm merely trying to contribute to this community.
...

Let's try an experiment, If you want to contribute to the forum community and have the education and background, there is a "New Topic" button and about 1600 other threads in here that the "pseudoscientist", and "perpetual motion nonsense" members like me have never posted on.

Start some educational threads or whatever on whatever topics you would like, you can also "bump" threads to the front page by simply posting to them.

I give you my word I will never post on any thread that you start or "bump" up to the front page, unless of course it is one where I am the OP.

On top of that, I'll make it easy for you. I'll take a vacation from the forum, so now it is all yours, you are free to reshape it however you like.

So far you have only "bumped" my "Pseudoscience" to the front page. Personally I would like to see some more, better topics by a well informed and knowledgeable scientist such as yourself.

You have the entire forum to reshape however you like.

Enjoy.

[stephenz]

now what?

now-what-2.png

now-what-1.png

edit: dummy numbers I used for dimensions happen to be the dimensions of a working engine, by the way.
Dead volume: includes the volume of everything that is not variable (i.e. that is not swept)
tell me you still don't see how Alpha's have greater compression ratio...

Start some educational threads or whatever on whatever topics you would like, you can also "bump" threads to the front page by simply posting to them.

../..

You have the entire forum to reshape however you like.

2 threads is all I have I think and more than I need.

And before you go, you asked for the math, so have a go at it.

[VincentG]

Unless I'm missing something...

Total positive displacement for the Alpha= 350
Total positive displacement for Beta/Gamma= 175

This is a perfect example of why there can really be no apples to apples comparison. This leaves us with the base geometric design limitations of the Alpha v. Beta/Gamma. This can be solved with a dwell mech on the Alpha, but now we're in a different ball park all together.

[stephenz]

it's apple to apple as it gets - the pistons and displacer have the same dimensions, and volumes are very comparable. The extra compression you get from an alpha is where its potential is; at the cost of a more difficult design (there is no cold piston, and sealing a hot piston is no easy task), and even less intuitive machine.

[Tom Booth]

now what?
now-what-2.png
now-what-1.png

edit: dummy numbers I used for dimensions happen to be the dimensions of a working engine, by the way.
Dead volume: includes the volume of everything that is not variable (i.e. that is not swept)
tell me you still don't see how Alpha's have greater compression ratio...

Start some educational threads or whatever on whatever topics you would like, you can also "bump" threads to the front page by simply posting to them.

../..

You have the entire forum to reshape however you like.

2 threads is all I have I think and more than I need.

And before you go, you asked for the math, so have a go at it.

Thanks,

Just at a glance, maybe you can help me out with something. What is this:

Resize_20240102_145754_4293.jpg (36.67 KiB) Viewed 2486 times

It appears at first glance that to get the Alpha volumes you are adding the volume of the cold cylinder and hot cylinder (V1+V2) AND the total volume Vt ? To get the volume V ??


Is this the equation you put into your program or spread sheet or whatever that is because the total volume in this graph seems extremely exaggerated.

Resize_20240102_145754_4149.jpg (66.27 KiB) Viewed 2486 times

For example, at crank angle 175 V2 is zero on the chart. And V1 is about 75

0 + 75 does not equal 225.

The volume Vt appears to have been trippled.

Are not V1 and V2 already in cubic centimeters?

That should be simple addition V1+V2=Vt

Not: V=V1+V2+Vt

Not entirely sure what you are doing there.


EDIT: I see, the last quantity in that equation is "dead volume" or Vd not "total volume" or Vt

Back to the chart, is the apparent tripling of the total volume due to the addition of dead volume?

If so that seems like an awful lot of dead volume in your Alpha. Triple the actual working fluid volume?

[VincentG]

The problem is that you've set an artificially fixed parameter of volume ratio on the Beta/Gamma to make a comparison to a physically fixed parameter for an Alpha. That's fine to make your case, but a bit of a stretch to use it to prove someone else here definitively wrong.

[Tom Booth]

The gamma and beta charts are similar but the total volume appears to be only doubled rather than trippled.

[stephenz]

The dead volumes are listed in the top left corner of the spreadsheet. they are based on an actual working (gamma) engine not some random numbers.
Beta has smaller dead volume to compensate for the lack of transfer tubes (5 cm3 in that engine).

"tripling" the volume due to dead volume is not something I understand here. The dead volume is equal to sum of all non-sweeping volumes: cooler volume, heater volume, regenerator and any other transfer tubes/clearances, etc. The optimal dead volume is the volume at which cooler, heater and regenerator volume will yield the least amount of losses. This is where the iterative process of the analysis takes place. It's a significantly non trivial step to go through. Every time you change a parameter you change the optimal parameters. So you keep adjusting parameters in an iterative manner until you converge to results, and in the even given you've done enough iterative steps you should end up with values are close enough to being optimal.

On this particular engine, cooler volume is 27cm3, heater volume is 73 cm3, regenerator volume is 35 cm3, transfer tube is 10 cm3, equaling 145cm3 of dead volume. I very generously reduced the total dead volume by 25cm3 on the Beta numbers, where 10 cm3 is probably all that was needed since the transfer tube is the only part that wouldn't be needed if this engine had been a Beta instead of a Gamma. As for the Alpha, the dead volume I used the same 145 cm3 which is vastly exaggerated for an Alpha considering the flow rates will be greater due to the increased swept volume but then again, a smaller figure would only prove my point further: Alpha compression ratio > Beta compression ratio > Gamma compression ratio.


as for you, Vincent, you now have both the equations and the spreadsheet. You can literally redo this yourself, verify my work, and punch in any number you want to see how things change. Your main point being:
- the Alpha has more swept volume, since it has 2 pistons.
- but the Alpha does not have the penalty of the displacer (which geometrically acts as additional dead volume).
- Alpha will ALWAYS 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.
- reducing the size of the pistons on the alpha will not reduce compression ratio if you keep the dead volume realistic.

If you don't believe that, then feel free to reduce the size of 2 pistons in the spreadsheet, (either by surface area or stroke - doesn't matter) and make sure you reduce the dead volume by the same amount, and run the numbers again. You'll see that the compression ratio of the Alpha is still well over 2.0.


I've done the work for you guys, provided the numbers.

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.

[stephenz]

The gamma and beta charts are similar but the total volume appears to be only doubled rather than trippled.

now-what-3.png

there is no tripling anywhere, for 3 sets of data, the equation is the same: V = V1 + V2 + Vd

[stephenz]

re-create the spreadsheet, come on this can't be that hard.
you got everything now, prove my math wrong.

you see that orange straight line on Gamma and Beta? there. That's what hurts Gamma and Beta. That's what makes Gamma the worst in compression ratio.

Does it matter? no.

It's still IMO the best platform to experiment on because it's by far the easiest to design around, machine, etc.

This thread is about high compression ratio and experimenting some new design. Awesome great, I'm genuinely all for that. No engine configuration will give you easier access to high compression ratio's than Alpha's. Beta's will need some kind of valving/solenoids are alike. Beta's kinetics are a Pita to manufacture.

[Tom Booth]

...

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.

....

Maybe this has something to do with it.

I do not treat the displacer as "dead volume", by the mere fact of its existence taking up space. Not if it is either solid or hollow but completely sealed.

It is not "technically a dead volume".

If it is a regenerative displacer of steel wool I could see considering it mostly dead volume, but that is a big if, and the Beta design I have in mind would most definitely have a solid or hollow sealed displacer, so I would not consider that "dead volume" as far as compression ratios are concerned.

[VincentG]

If you don't believe that, then feel free to reduce the size of 2 pistons in the spreadsheet, (either by surface area or stroke - doesn't matter) and make sure you reduce the dead volume by the same amount, and run the numbers again. You'll see that the compression ratio of the Alpha is still well over 2.0.

If you track the gas mass of a standard 90 degree Alpha with equal size cylinders, you'll see that this compression ratio doesn't actually play out so well.

[stephenz]

If you track the gas mass of a standard 90 degree Alpha with equal size cylinders, you'll see that this compression ratio doesn't actually play out so well.

compression ratio is a geometric figure. I mentioned this a couple of pages ago. It has nothing to do with gas whatsoever.
Don't confuse ratio (i.e. volumetric compression ratio) and pressure ratio.

Don't get me wrong, I am not saying Alpha's are the same solution. They may be, but they're definitely not when it comes to me personally. The engineering challenges lying with Alpha's are to me much greater than Gamma's or even Beta's.

[stephenz]

Maybe this has something to do with it.

I do not treat the displacer as "dead volume", by the mere fact of its existence taking up space. Not if it is either solid or hollow but completely sealed.

It is not "technically a dead volume".

If it is a regenerative displacer of steel wool I could see considering it mostly dead volume, but that is a big if, and the Beta design I have in mind would most definitely have a solid or hollow sealed displacer, so I would not consider that "dead volume" as far as compression ratios are concerned.

It doesn't matter how you call it, the displacer swept volume is constant with the crank angle (that straight lines on the chart). It doesn't matter how it seal, it only matters that it does not contribute to the variation of the engine's volume vs crank angle. This is because all sides of the displacer piston see the same pressure (minus the negligible difference due to the displacer rod).

[VincentG]

compression ratio is a geometric figure. I mentioned this a couple of pages ago. It has nothing to do with gas whatsoever.
Don't confuse ratio (i.e. volumetric compression ratio) and pressure ratio.

This is simply not true for an ECE hot air engine and is fundamentally the single most misunderstood aspect of them.