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Talk:Stirling engine/Archive 6

< Talk:Stirling engine
Latest comment: 3 years ago by 71.84.136.105 in topic Efficiency
Archive 1 ← Archive 4 Archive 5 Archive 6

thesis statment

Latest comment: 11 years ago1 comment1 person in discussion

The technical explanation was exemplary, but I pity the non-technical person trying to figure out how this engine differs from, say, an auto engine. It's sometimes hard for a technical person to simplify at the beginning and not reflexively use technical jargon in an initial explanation, but doing so in this article would increase its value a lot. Pb8bije6a7b6a3w (talk) 14:30, 27 November 2012 (UTC)

Yes, the cycle-principle could be said more concisely, at the top of the article; and then, after that, the actual engine-operation principles for Alpha, Beta & Gamma could be explained more completely.

The article has immense detail, but seriously lacks prompt, concise and complete exposition & explanation.

Hot to cold cylinder ratio

Latest comment: 10 years ago1 comment1 person in discussion

The relative sizes of the hot and cold cylinders appears to be important. Could the equations or ratios be added? Andrew Swallow (talk) 17:35, 28 August 2013 (UTC)

The Battle Of Danzig - Corridor IC - Germania Rested.

Latest comment: 10 years ago1 comment1 person in discussion

'n' pairs of pistons at a given phase difference can be arranged with interconnecting exhausts and temperature variants. this does not constitute a unique engine.


engine cycle postulates:

spark for fuel-air is assumed to drive the isochoric power stroke.

fuel injector for compression reciprocating is assumed to drive the isobaric power stroke.


the case closest to that of an isobaric-isochoric system, if achieved - will be efficient.

ASG

117.238.252.143 (talk) —Preceding undated comment added 08:34, 15 September 2013 (UTC)

Efficiency

Latest comment: 3 years ago2 comments2 people in discussion

This article states that the "theoretical thermal efficiency [of the Stirling engine] equals that of the hypothetical Carnot cycle". Yet other sources, such as here, state otherwise. Is this an error? Arbitrarily0 (talk) 23:53, 24 September 2013 (UTC)

The ideal Stirling Cycle has the same efficiency as the Carnot Cycle.

But a different "ideal" Stirling Cycle has been propoposed--one with the isothermal processes replaced by adiabatic processes...argued-for by a claim that the actual Stirling's compression & expansion are more nearly adiabatic than isothermal.

So it just depends on what you mean by "ideal". Most sources seem to agree in calling "ideal" the cycle with isothermal compression & expansion, probably because that's indeed ideal, and it's the intention of the Stirling.

The Stirling Cycle with adiabatic compression has been called the "Adiabatic Stirling Cycle", and that seems a much better name for it, to avoid confusion with the more-ideal, sought-for, Ideal Stirling Cycle with its isothermal compression & expansion. — Preceding unsigned comment added by 71.84.136.105 (talk) 05:29, 15 January 2021 (UTC)

Thermoacoustic cycle

Latest comment: 9 years ago1 comment1 person in discussion

Though it is not the main topic of the article, I found the paragraph about the "Thermoacoustic cycle" intriguing. But I think a sentence is probably imprecise, that is "High-amplitude acoustic standing waves cause compression and expansion analogous to a Stirling power piston". I don't think standing waves play a role in the compression phase here. They should be limited to expansion (piston out). Then air loses energy, cools down and the piston is brought back. In other words, the temperature difference at one end of the cylinder originates a (imprecise) standing wave which is corrected and amplified in the resonator and once powerful enough it can strike the piston. The returning low-power (standing) wave pushes air through the cold heat exchanger where it experiences a small pressure drop, gives off heat and its volume is reduced so that the piston can move back... 

 — Preceding unsigned comment added by 79.31.206.129 (talk) 17:45, 12 March 2015 (UTC)

External links modified

Latest comment: 8 years ago1 comment1 person in discussion

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Latest comment: 8 years ago1 comment1 person in discussion

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Alpha configuration

Latest comment: 3 years ago6 comments5 people in discussion

I believe the alpha configuration should not be featured so prominently in the description of the working of Stirling engines for multiple reasons: 1) is not the traditional one, Robert Stirling always built Beta/Gammas if I understand it right. 2) it's very little featured among the commercial models, in fact I couldn't find one. 3) even from a theoretical standpoint an alpha configuration seems very unattractive, for example its two cylinders, as working cylinders, are equivalent to one with intermediate phase and cross section only square root of two bigger than one of the two, the swept and work displacements are the same, and more. The really generic configuration of a Stirling engine is the gamma, of which the beta is a special case with added constraints and alpha is another one with more constraints and so many drawbacks that almost nobody employs it. Discussing with friends, learning about the engine for the first time, I have noticed that they all struggle to understand it taking the alpha as a paradigm. Using the gamma is a lot easier.

Reply:

Yeah? Then explain to them why,during the power-stroke, the Beta has the heat-sink removing heat from the air that's expanding to push the work-piston. It seems that there'd be some loss of efficiency due to the heat-removal, by the heat-sink, from the expanding air.

Oh yes, and you might also want to explain to them how it is that the hot air, in in the hot-region, is able to flow around the displacer, to take part in the expansion against the work-piston, and yet, when the displacer moves, to displace air between the hot and cold regions, it forces that air to flow through the regenerator.

The Beta-Configuraration isn't well-explained. The Alpha-Configuration is completely straightforward, with all 4 of the approximate Stirling-Cycle processes being accomplished by the motions of the two pistons operated by the crank. — Preceding unsigned comment added by 71.84.136.105 (talk) 05:51, 5 January 2021 (UTC)

I propose to change the article to reflect this.

Reply:

You'd need to give better reasons, &/or cite sources for what is otherwise just your personal evaluation. 

but please comment I am not an expert, just  a reader.

— Preceding unsigned comment added by 82.56.177.242 (talk) 08:04, 17 May 2016 (UTC)

I've never come across an Alpha configuration engine but I haven't really been looking. I agree, if they exist, they are pretty rare. However, the configuration is probably not as unattractive as the drawing would imply. The drawing shows the two cylinders operating on a common crank. This illustrates the principal clearly. In practice, though, if one was being made, it would probably have two separate cranks, set at 90 degrees to each other, with the cylinders mounted parallel to each other.

Reply:

In the NASA Stirling project's automotive Stirling Engine for the Chevy Celebrity, that Alpha-Configuration had 4 cylinders (that is, 2 pairs of cylinders) in a V-arrangement, with the 4 pistons all using the same crankshaft.

The important characteristic of the alpha configuration is that there are separate hot and cold cylinders acting on the crankshaft in 90 degrees phase to each other. In terms of power/weight ratio, it would probably be less efficient than the beta or gamma configurations, but it has the advantage of simplicity and, hence, reliability. Another advantage is the fact that, the hot and cold parts being completely separated, thermal insulation between the two can be much better. Power/weight ratio is not one of the Stirling engine's big advantages, anyway. --Roly (talk) 08:51, 17 May 2016 (UTC)

What has to be at 90 degrees for effectiveness in a sinusoidal engine are not the two cylinder movements but the pressure and volume variations which is achieved with a work cylinder separate from the displacer. By sharing the two functions necessary for an engine to work between the two cylinders it makes unnecessary and inefficient compromises . The 2 functions are the one of extracting mechanical energy from the engine via the work cylinder and the one of heating and cooling the fluid, the task of the displacer in the other configurations. You must agree that for the first function the two cylinders are equivalent to one whose cross section is √2 of the cross-sections of the individual cylinders and whose phase is 45 deg from each one of the two. It's a consequence of the two pistons being connected at the same crankshaft and being exposed always to the same pressure. It can be seen more clearly imagining to increase continuously the relative phase between the two equal cylinders from 0 to 180: at 0 the 2 cylinders are in phase and equivalent to one twice the cross-section and at 180 they don't do any work on the gas, the gas volume remains unchanged in time at the turn of the crankshaft. The situation changes smoothly going from one extreme to the other and 90 deg is right in between. This has serious consequences: 2 pistons instead of one, more friction losses, a rigid phase delay of the wrong amount. There are many other drawbacks of the alpha, which is why you never see it: a rigid ratio between swept work volume to displaced volume, potential overheating of the seals of the hot cylinder, just to name two. On the other side in the gamma configuration, of which from this perspective the betas are a subset, shuffling the gas around and extracting work are decoupled functions being performed by separate devices, the piston and the displacer. All the previously mentioned issues disappear. — Preceding unsigned comment added by 82.56.177.242 (talk) 13:09, 20 May 2016 (UTC)

  • Alphas are rare because most Stirlings are low power toys and at that scale a displacer is easier to make work than a static regenerator.
The important point, and why they still deserve prominence, is because they're how Stirling first conceived the engine - using a regenerator. This should be explained in a history section. We also need a better image. The impression here is that "An Alfa [sic] is anything at 90º", which is both wrong in itself (it's regenerator not displacer which matters) and it also leads to confusion with a Gamma. By phasing the crankpins you can make either of these as either parallel or V engines.
I would agree though that an explanation of the basic principle probably starts most simply with a Gamma, as does a description of available engines today. Andy Dingley (talk) 09:21, 17 May 2016 (UTC)

I believe the issue of the regenerator is an independent issue, it can be present or absent in all configurations. It's true that toy engines are rarely alphas but that's because alphas can't have a large swept volume compared to the work piston swept volume. At low temperature differences it is practically a requirement. Look at LTD engines, toys or otherwise. As far as the alpha being the way Stirling conceived the engine I don't think so, look at the original patent, it's a beta, that is a gamma with a displacer the same cross section of the work cylinder http://www.stirlingengines.org.uk/pioneers/pion2.html At the end I think that classifying various designs in the 3 categories of alpha, beta and gamma is unnecessarily confusing. It complicates the issue of explaining how the engine works for a beginner, it doesn't help a more sophisticated discussion, it's not complete anyway since it leaves other categories out. Does any body know where does it come from? Has it ever been recognised by any authority of the field? I propose to eliminate it from the article. — Preceding unsigned comment added by Omblauman (talk • contribs) 10:17, 22 May 2016 (UTC) 82.56.177.242 (talk) 13:52, 20 May 2016 (UTC)

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Latest comment: 7 years ago1 comment1 person in discussion

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External links modified

Latest comment: 6 years ago1 comment1 person in discussion

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References

Latest comment: 6 years ago3 comments2 people in discussion

A published paper can be referenced. So can reports in local newspapers. Andrew Swallow (talk) 22:36, 17 April 2018 (UTC)

Yes, depending on the reliability of the authors and publishers. Is there something specific you are concerned about? —DIYeditor (talk) 22:57, 17 April 2018 (UTC)
My comment was aimed at the person whose addition you removed, DIYeditor, on the grounds it did not have a reference. The optimal shaft length being dependant on π could be useful in other implementations. Andrew Swallow (talk) 01:05, 18 April 2018 (UTC)
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