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Hi.

Does essex engine configuration belongs to beta or gamma type of stirling engine ?



For me it looks like more beta, because it is possible to reduce dead volume on compression stroke - power piston can follow into displacer area like in beta type ?

Staska, it resembles a BETA type, just that the hot end is at the other end from normal, different, not too sure about the cooling which is just as important as the heating. Was a motor built and run from this design?
Ian S C

Yes, it does run. And there are kits in normal price: http://myfordboy.blogspot.com/p/the-ess ... ngine.html By original it was adverted as 1/40th hp engine. Or 1/10hp if double cylinder ?

http://books.google.com.au/books?id=iOA ... es&f=false

It had a lot of interesting videos on page too. I had contacted with author, it does not disclose any dimensions for calculating any raw data. It looks like be 4x3 cm bore and stroke for displacer, taken from this photo: http://2.bp.blogspot.com/-5ydrHlD-Q9U/U ... cs+010.jpg and to know that Flywheel diameter is 6"

For me it is perfect kinematic to be made from any two cylinder engine with 180 bended crank shaft and pushrods, and to allow small pressure without sealed crankcase.

Does any-one have any ideas ? Does essex stirling engine is the answer to question about typical 1/1.5 ratio of power piston to displacer found in normal gamma engines with cold expansion space ?

Interesting info :http://arc.aiaa.org/doi/abs/10.2514/6.1994-3952 or http://papers.sae.org/929026/

Quote:

It was demonstrated by analytical means, that the specific work obtainable from a Stirling type engine, with separate power and displacer cylinders, having the power cylinder connected to the hot zone of the displacer cylinder is, for typical operating conditions, about twice that obtainable when the power cylinder is connected to the cold zone.

Ahh yes, but has it been proved practice, analytics is one thing, but hard metal is (sometimes) another.
Ian S C

Yes.

http://www3.nd.edu/~me463d18/Files/Dere ... esting.pdf

With essex, it should be even better - we could negate any dead space with common swept volume. But - gamma gives posibility to make thin-tube heat exchanger for hot end without additional piston ring...

"academics" http://papers.sae.org/929026/, http://arc.aiaa.org/doi/abs/10.2514/6.1994-3867 , http://arc.aiaa.org/doi/abs/10.2514/6.1994-3952 (i even bought last one) says up to 1.6-1.7 more power from.

But - it is possible what in real engine with have 100 watt minus 30w = 70 watt for friction, for heat side vork extraction we have 170 watt - 30 watt - 140w

I recall reading about a scientist that was exploring a remote cave, and discovered an un-listed animal that had six legs. By the rules of animal study, it was an insect, with the number of legs being the most important characteristic above all others.
However, it "looked like" a spider.

It ate like a spider, it reproduced like a spider. It injected venom into its prey with tiny fangs, just like a spider. It was indistinguishable from being a spider by every possible metric...except the number of legs. The fellow argued with his university, and they settled on calling it a "wingless fly", because the rules for nomenclature are well established now.

After examining the Essex for a while, I am convinced it is a Gamma, even though the displacer and power piston both use the same cylinder (from opposite ends). I say this while still accepting that it does have some characteristics of a Beta.

I say this because from my perspective, one piston is a power piston, and the other is a loosely-fitted displacer, which allows pressure to surround it equally, with its only job being to force the working gas back-and-forth between the hot and cold areas.

That being said, I am looking for examples of an Alpha that uses one cylinder (similar in appearance to the Essex) but the two pistons interact from either end, with a regenerator in the center. Pics courtesy of "myfordboy", with his lathe being a "Myford" brand tool.

staska wrote: ↑Wed May 28, 2014 2:00 pm
For me it looks like more beta, because it is possible to reduce dead volume on compression stroke - power piston can follow into displacer area like in beta type ?

Very interesting. I had thought as much, but not having the actual engine I wasn't completely sure.

I'm wondering if any Essex engines incorporated a regenerator or inline type regenerative displacer. That is, a displacer with a built in regenerator component.

I've debated the usefulness of a regenerator in my own mind for a long time. Logically I couldn't see the benefit. Experimentally however, it seemed to make a difference, but I couldn't figure out any good reason why it seems to provide some kind of power boost.

I think I may have finally figured it out, maybe.

viewtopic.php?p=22527#p22527

Anyway, I'm thinking now that the Essex WITH REGENERATOR, could effectively implement a kind of regenerative "heat storage and retrieval", perhaps better than other arrangements.

Rather than the displacer merely uncovering or exposing the hot cylinder walls, a regenerative displacer could effectively increase heat input by exposing the hot cylinder walls while simultaneously releasing heat from the regenerator.

A regenerator would likely also absorb and store additional heat to help cool the working fluid for the return stroke.

AFAIK however, no Essex engine ever employed a regenerator or regenerative displacer.

Kind of reminds me of my old "hot potato" engine
Or the more recent "Ringbom" type actuated "hot potato"

viewtopic.php?p=22527#p22527

Both are Essex type single cylinder opposed piston but with regenerative displacers and lacking the mechanical arm arrangement of the Essex.

In the lower image, the elevation in pressure from the approaching power piston pushes back the regenerative displacer, Ringbom style, exposing multiple heat exchange surfaces.

staska wrote: ↑Sun Jun 08, 2014 11:58 am Does any-one have any ideas ? Does essex stirling engine is the answer to question about typical 1/1.5 ratio of power piston to displacer found in normal gamma engines with cold expansion space ?

If you're asking about the stroke lengths, it's around 1:0.6 displacer/power-piston ratio according to the data given for this half scale model in the video description.
https://www.youtube.com/watch?v=38hNrAg2dT4

Here's a partially dismantled twin:


2" Bore
7 1/4" Flywheel

Due to the thin brass walls(.015") of the main tube, displacer and power piston, the original Essex has pretty effective regeneration without any additional dead space or flow restriction. I'll try to film a thermal video to show this later.

VincentG wrote: ↑Tue May 07, 2024 7:10 am Due to the thin brass walls(.015") of the main tube, displacer and power piston, the original Essex has pretty effective regeneration without any additional dead space or flow restriction. I'll try to film a thermal video to show this later.

True to some degree I guess. But a "regenerator" that depends on the annular space between the displacer and cylinder walls, I would think, is losing much of the heat to be regenerated to the surroundings.

I might make the cylinder less conductive, ceramic perhaps, to retain heat and a regenerative displacer having the regenerator through the center. The outside of the displacer also non-heat conducting.

The Vuilleumier heat pump patent for example shows the regenerative displacers:
5 & 6 are the displacers
7 & 8 the center regenerative portion.

With such an arrangement the sequestered heat is much more effectively preserved as opposed to the outer walls of a metal cylinder.

Imo the Essex works so good with such a simple design because it makes no attempt at traditional "regeneration" and instead makes an attempt at minimizing thermal mass.

I would wager that any attempt at adding on a traditional regenerator would lower specific power output.

Again, imo, in practice, most gains seen from a regenerator actually come from its ability to reduce convection losses and in some cases prevent the displacer itself from heat soaking.

Do I know what I'm talking about? Probably not.