Stirling engine made from scroll expander

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Response to Stirling engine made from scroll expander

Postby bptdude___2569 » Mon May 04, 2009 6:39 am


wow...

Robert is ramblig a bit!?
Well, I have rambled before, but I think he does not understand the unique properties of a Stirling, he does not understand we are here to promote that particular engine design, and he has some fear of exploding oils that is beyond reason.

:)

I suppose a better question would be if a scroll expander type displacer/piston would help a Stirling design.

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Response to Stirling engine made from scroll expander

Postby davidha » Thu Jul 02, 2009 5:44 pm

Looking at an old thermodynamics text with a schematic for a Stirling power cycle, it looks like a heated scroll expander piped to and from a cooled scroll compressor might work. Why not use air as the working gas? Of course the in-between pipes will need to make a heat exchanger for regeneration. By the way, each scroll unit will have a fixed scroll and an orbiting scroll, and more than one moving part to define the orbit. We also need a linkage to deliver power from the expander to the compressor. No, I have not made one, but I would like to.
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Response to Stirling engine made from scroll expander

Postby stan.hornbaker » Sat Jul 04, 2009 8:27 am

Two scroll expander/compressors interconnected do not constitute a Stirling engine out of date textbooks to the contrary. The fluid (gas, usually air) in a Stirling undergoes repeated cycles of heating-expansion, cooling-contraction producing an amount of mechanical output energy in the process.

A two scroll machine would be less efficient than a standard type Stirling.

A scroll expander running as a "Solar motor" would be problematical at best it it would run at all.
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Response to Stirling engine made from scroll expander

Postby davidha » Sat Jul 04, 2009 9:39 am

My old text makes no mention of scrolls, none in the entire text. It shows a heated expander and a cooled compressor connected by flows through the regenerator, and briefly explains the Stirling cycle (with p-v and T-s diagrams). It seems that regular pistons were assumed instead of scrolls.

As I understand scrolls, from diagrams, animations and texts from the internet, they are an ingenious way to compress and expand a gas. Their efficiency is a function of how perfectly they are built to match the mathematical curve. With a tight enough tolerance (and/or use of a sealing lubricant) very high efficiencies are possible. But looking at modest power production and plenty of space in a stationary application, and with a substantial heating load, low efficiency (even very low efficiency) works for me.

We have a high temp and a low temp, what is the simplest effective heat engine we can build? Maybe it involves two scrolls and a regenerator? Maybe it is not technically a Stirling?
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Response to Stirling engine made from scroll expander

Postby stan.hornbaker » Sat Jul 04, 2009 2:57 pm

The simplest implementation of any device is usually the best. Avoid any complications to avoid the disappoint of failure.

Go to StarSpin.com and click on Stirling engines. Select Jim Dandy #6 to see a 2-1/2 HP Stirling engine run on wood.

Andy Ross of Ohio build several Stirling engines in various configurations. His book is no longer in print.

John Erricson built commercial versions of a modified Stirling engine to pump irrigation water in the west around the turn of the last century. Also build a huge side wheeler ship driven by a hot air engine of his design.

Stirling Energy Systems is touting a new iteration of an improved solar dish technology to drive a Stirling engine located at the focus of the dish. See: http://www.stirlingenergy.com/pdf/2009-06-23.pdf

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Response to Stirling engine made from scroll expander

Postby vladsabin » Wed Dec 16, 2009 5:49 pm

This topic acurred to me, because I work with scroll compressors and I try to understand perhaps more about physics that are involved in such a machine.
The truth is I had these day's the idea to try to build a scroll engine based on a scroll expander, that would would work on any known fuel(combustible) that exists. I am speaking of an engine that would work, from my point of view, as an invertet ventilator system. If my air ventilator works as an compressor, than my engine would work in the oposite way as a dynam using the shape of the van.
The main idea is to use the scrolls compressor mobile part shape, like a wind mill that transforms energy of the moving gas(due to expansion) for creating working force.
Of course using an shock expansive gas as gazoline type fuel would probably result in the the destruction of the scroll, perhaps a redesigning of the scroll compressor would solve this problem. I mean the redesigning of the scroll in the way that it would enable the expansion gas to be used in the most efficient way posssible, whithout creating shocks in the system and almost any expanding energy not to be dissipated in a shock. For this you would need an a shape that is similar to the scroll compressor but wich goal is to calm down the energy of the shock and and transform it along the spiral into working force.
The oiling system of such an engine would be the second bigest problem, but still it can be solved. As well as the fact that this engine would need to have a friction area between the mobile and fixed scroll which would result in an, most probabily, imposibilty of designing an hermeticly closed space between the two scrolls.
PS: Sorry for my english :P
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