Stirling essex - beta or gamma ?

[Tom Booth]

You could be right. I would have basically agreed up until yesterday, given my newly found "inspiration" that a regenerator is actually, perhaps, more for cooling. To take heat temporarily out of the picture during compression, rather than for just conserving heat necessarily.

I can say, at any rate, all my experiments that appeared to have the engine cooling slightly below ambient were LTD engines to which I had made the displacer VERY close fitting and retrofitted a regenerator in the sidewalls so the air flow from hot side to cold side and back was almost entirely through the regenerator.

Also with better heat containment and control, switching from an aluminum to pumice stone displacer for example. A high temperature engine that was difficult to get started with a propane torch with aluminum started and ran fine on a trimmed down tea candle with better heat retainment.

My main observation anyway is that the heat capacity of the working fluid is limited and the working fluid must expand and do work when heated. It does not appear to TRANSFER heat THROUGH the engine to any great extent at all.

Problems with overheating, heat soaking, heat loss, inefficient heat use generally, is not an issue having much to do with the working fluid but much more likely other materials containing the working fluid, conducting heat AROUND the working fluid rather than expanding it to produce work.

From what I've seen Essex engines are heat hogs. They need a lot of heat to start up and keep running. I imagine a big Essex with a regenerative displacer running on "heat of the hand". LOL.

Maybe a bit overoptimistic.

At least I would think the engine could potentially be much more frugal in its heat requirement with the addition of a proper regenerator.

Of course, it's just theory. Maybe I'll try building a small model Essex type model with a regenerator sometime to see if it performs as well as I imagine.

[staska]

So many time passed since my interest in essex stirling.

So - no, it is not a beta, it is hot end connected gamma stirling. Some better usage of working fluid compared to plain gamma.

[VincentG]

I'm not sure what really defines either, but by my logic it's a Beta for the following reasons.

1- Both piston and displacer share the same exact bore and axis of travel.

2- Most importantly, the displacer and power piston occupy the same space at various points of the cycle, a feature reserved for pancake Gammas and Betas imo.

3- If the power piston had a pass through linkage to displacer it would not even be a question...but is that what defines a Beta in the first place?

[Fool]

All betas are gammas, but not all gammas are betas. Alphas are different, and similar.

[matt brown]

I'm not sure what really defines either, but by my logic it's a Beta for the following reasons.

1- Both piston and displacer share the same exact bore and axis of travel.

2- Most importantly, the displacer and power piston occupy the same space at various points of the cycle, a feature reserved for pancake Gammas and Betas imo.

3- If the power piston had a pass through linkage to displacer it would not even be a question...but is that what defines a Beta in the first place?

Fool - take note, Vincent has this correct. Although both betas and gammas have displacers, the gamma hallmark is a distinct working cylinder. So, this makes the Essex a "hot" beta vs the common flavor. I've never been able to track down the origins of alpha-beta-gamma buzz, but this likely evolved from Graham Walker or Theodor Finkelstein in late 1960s. During the first Green Movement (1970s) all Stirlings had displacers and were driven off the 'cold side'. Back then, the later 'alpha' was simply known as Rider type/style.

[Fool]

I agree with calling the Essex a beta.

I was pointing out the similarity of the gamma beta debate ah, to the square rectangle classification. All squares are rectangles, but not all rectangles are squares. All betas are gammas, but some gammas have the displacer cylinders further apart than others.

A gamma is a displacer and piston combination. A beta is a displacer piston combination. The beta has both in a single cylinder. The gamma just has a larger separation and narrower connection. This is similar to a rectangle having two sides separated further. I'm not the first to mention this.

My point is the whole gamma verses beta debate is miniscule. The pancake LTD's sort of demonstrate this.

[staska]

Beta vs gamma vs alpha - just buy Allans book.

They are same, and could be transformed to same mathematically equal gas path. Except some betas with high "minus" volume.

But all else - yes.

[matt brown]

One major difference...hot gamma has more output for same regen than cold gamma and hot beta has more output for same regen than cold beta. Even with excellent regen, this is usually a big difference in overall efficiency. An alpha has the lowest regen and the best torque (everything else equal).

[staska]

One major difference...hot gamma has more output for same regen than cold gamma and hot beta has more output for same regen than cold beta. Even with excellent regen, this is usually a big difference in overall efficiency. An alpha has the lowest regen and the best torque (everything else equal).

Could i ask for source of this information ? Alpha have 1.41 more cc at 90 phase angle. Beeing all other equal. Gammas do.suffer from lowest working fluid beeing heated and putted to work. Or all extra dead space is cushion to absorb pur precise pressure. Add some valves to remove cold cushion - gamma will be same or better than beta.

But this is anothoer, and long discussion

This one is valved, hot end connected gamma:

http://hotairengines.org/open-cycle-eng ... ir-machine

[matt brown]

One major difference...hot gamma has more output for same regen than cold gamma and hot beta has more output for same regen than cold beta. Even with excellent regen, this is usually a big difference in overall efficiency. An alpha has the lowest regen and the best torque (everything else equal).

hot vs cold PP gamma.png (22.17 KiB) Viewed 4389 times

staska - I posted this somewhere on forum a while back. Note several things:

(1) m = gas mass (not moles) exclusive clearance and conduit volumes (added for clarity)
(2) graphic is shown as distinct events
(3) both have same regen
(4) both have 12m regen but each only uses 6m for output
(5) regen 'load' is (regen heat)/(input heat)
(6) whatever the regen load (requires calcs) it is doubled by only 1/2 the gas mass producing output
(7) this remains a major downside to any gamma or beta but moreso when 'cold' output
(8) Pmax is when PP is TDC, so torque remains an issue unless linear generator
(9) both use 6m for output, but hot PP has 2x the output due to 2x cold PP volume

A similar ideal alpha with distinct events will use all its gas mass to produce work. The major takeaway for regen cycles is that each cycle (rpm) requires 2 regen passes, so if you have regen=.9 PER PASS then you have regen =.9x.9=.81 PER CYCLE. Then you can factor this thru your regen load to discover why most consider Stirlings a joke. The more you study this stuff, the more you will understand why there's no 'working' Stirling except niche markets.

Now, simply digest all that and then consider typical out-of-phase issues that further sink any scheme...

[matt brown]

Could i ask for source of this information ?

I've been studying this stuff for 50 years...

Alpha have 1.41 more cc at 90 phase angle. Beeing all other equal. Gammas do.suffer from lowest working fluid beeing heated and putted to work. Or all extra dead space is cushion to absorb pur precise pressure. Add some valves to remove cold cushion - gamma will be same or better than beta.

But this is anothoer, and long discussion

This one is valved, hot end connected gamma:

http://hotairengines.org/open-cycle-eng ... ir-machine

I like the idea of valves, cams, etc...anything that reduces or eliminates the typical out-of-phase dynamics that plague common SE. However, 2 conventional issues remain inherent to SE (1) regen (2) input.

[Stroller]

When is air being vented to atmophere by the Wilcox engine? The first half of the compression phase?

[matt brown]

When is air being vented to atmophere by the Wilcox engine? The first half of the compression phase?

Yes, but I think first half of the compression piston stroke would be a better description.

The output per cycle was likely so low that it required a team of horses to spin up the flywheel prior starting. It's almost an open cycle Stirling where the "hot side" is almost a displacer. If the designers survived until the Essex, I wonder what they thought...

[matt brown]

staska - here's the hot/cold gamma comparison within same values where both gamma have same PP volume - enjoy

hot PP_1.png (23.11 KiB) Viewed 4359 times

[Stroller]

Yes, but I think first half of the compression piston stroke would be a better description.

Thanks, that is what I meant.

The output per cycle was likely so low that it required a team of horses to spin up the flywheel prior starting. It's almost an open cycle Stirling where the "hot side" is almost a displacer. If the designers survived until the Essex, I wonder what they thought...

It seems two horsepower was claimed. Maybe they were Shetland ponies?
So when does air get drawn back in? Surely not during expansion, when there will be positive pressure??