Stirling Engine Advance

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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ladajo
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Stirling Engine Advance

Postby ladajo » Wed Jun 15, 2016 5:48 pm

I thought this interesting, and only a matter of time.

http://www.khou.com/features/san-antonino-man-has-engine-that-gets-100-mpg/242673922

Any heat source will do, say a polywell perhaps? Sterling efficiency makes it a prime replacement candidate for traditional heat engine approaches.
They have even been looked at for orbital power generation using hot rocks. I need to refresh myself on the current TEG efficiencies in contrast. Albiet with TEG, you get to lose the moving parts part of the argument.
Last edited by ladajo on Wed Jun 15, 2016 7:29 pm, edited 1 time in total.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)
What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

KitemanSA
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Re: Sterling Engine Advance

Postby KitemanSA » Wed Jun 15, 2016 7:01 pm

FYI:
Sterling is silver
Stirling is engine.

ladajo
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Re: Stirling Engine Advance

Postby ladajo » Wed Jun 15, 2016 7:30 pm

Fixed, thanks! I did not notice my error.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Tom Ligon
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Re: Stirling Engine Advance

Postby Tom Ligon » Wed Jun 15, 2016 7:48 pm

I was thinking that was an error.

The article is vague about just what the advance is, or how they're using it with a TEG. I would think they ought to beat the pants off existing thermopile TEGs if you don't mind the bulk and moving parts.

It did prompt me to look up Stirling engine kits again. I sure waste a lot of heat up the chimney on the wood stove.

I had a co-worker who left our lab to go work for a Stirling engine start-up back around 1980. I never did hear anything from it.

Tom Ligon
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Re: Stirling Engine Advance

Postby Tom Ligon » Wed Jun 15, 2016 7:55 pm

The fine print on this toy (in the e-bay ads for it), says it is not intended for use on a woodburner stove top. However, it ought to work.
http://www.pmmodelengines.com/shop/sola ... -engine-6/

But this one is for wood stoves:
http://www.gyroscope.com/d.asp?product=VULCANSTOVEFAN

Not that converting the Fisher Baby Bear is going to produce a 100 mph stove. But I have been contemplating an improved heat exchanger for the stack. Using a Stirling fan for the circulation would make a lot of sense, and the speed should rise with flue gas temperature.

Diogenes
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Re: Stirling Engine Advance

Postby Diogenes » Thu Jun 16, 2016 11:16 pm

ladajo wrote:I thought this interesting, and only a matter of time.

http://www.khou.com/features/san-antonino-man-has-engine-that-gets-100-mpg/242673922

Any heat source will do, say a polywell perhaps? Sterling efficiency makes it a prime replacement candidate for traditional heat engine approaches.
They have even been looked at for orbital power generation using hot rocks. I need to refresh myself on the current TEG efficiencies in contrast. Albiet with TEG, you get to lose the moving parts part of the argument.




I find that story quite annoying. I thought of that idea back in the 1990s, and i'm sure a lot of other people did as well. Coupling a Stirling engine to a generator is not an idea I would consider particularly brilliant, and the article also makes a mistake on the efficiency of a regular internal combustion engine.

The rule of thumb that I have always heard was that a gasoline engine achieves a maximum theoretical efficiency of 35%, a diesel 40%, and a Stirling engine something along the lines of 45%.

An Otto cycle engine in a similar configuration (driving a generator while running at a constant speed. ) would only be a little less efficient, and a diesel in the same configuration would be almost as good.

If optimized through the usage of the Miller cycle, a diesel might be indistinguishable from a Stirling in terms of effeciency.


Where the Stirling would show a marked improvement is in reduced weight and simplicity. No noxious chemical exhaust system, no cooling system, and lighter materials useable for construction.


I give the guy props for actually building something though.
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
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Diogenes
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Re: Stirling Engine Advance

Postby Diogenes » Thu Jun 16, 2016 11:24 pm

Tom Ligon wrote:I was thinking that was an error.

The article is vague about just what the advance is, or how they're using it with a TEG. I would think they ought to beat the pants off existing thermopile TEGs if you don't mind the bulk and moving parts.

It did prompt me to look up Stirling engine kits again.



I built a low temperature Stirling out of pieces of a hard drive and other bits of junk. I used an eyeglasses hinge as my connecting rod. It worked pretty good on a cup of hot water, but I never got it down to that few degrees differential.



Tom Ligon wrote:
I had a co-worker who left our lab to go work for a Stirling engine start-up back around 1980. I never did hear anything from it.



Not enough benefit to make it worth the trouble I expect. High efficiency yes, but low power unless you build it really big.

Regular engines put something like 800 psi on the piston surface. Stirlings are considerably lower pressure, so you have to build power with area and repetition.
‘What all the wise men promised has not happened, and what all the damned fools said would happen has come to pass.’
— Lord Melbourne —

ladajo
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Re: Stirling Engine Advance

Postby ladajo » Fri Jun 17, 2016 2:28 am

There is also a new rotary coming on the market. It is a reverse configuration wankel. So the rotor is lobe shaped (like the wankel casing), and the casing is a tri-lobe. They have built this one as well, and are now ramping up development for cars/truck applications. I think it would also do well as a gen/or hybrid unit, especially if you used a turbo to capture exhaust gas energy as well.

I have always liked rotary engines, and think this one is even better. Not sure on efficiencies. It also made me think of an adapted gas turbine design. At the end of the day, it is always suck-squeeze-bang-blow.

http://www.popularmechanics.com/military/research/a15233/liquidpiston-darpa-contract/

http://liquidpiston.com/
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Tom Ligon
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Re: Stirling Engine Advance

Postby Tom Ligon » Fri Jun 17, 2016 4:04 am

My understanding or Wankels is that their compression ratio is poor, and the odd combustion chamber shape produces an uneven burn. They make good power for their weight but they tend to be inefficient.

Makes Shadow 200 run like a bat out of hell, though.

An inverted Wankel ... wouldn't that be a bit like the Gnome radial, where the whole engine turned and the crankshaft stayed stationary? Those had horrible gyroscopic effects. But rotating Stirlings have been used to move the cylinders from heat source to sink.

ladajo
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Re: Stirling Engine Advance

Postby ladajo » Fri Jun 17, 2016 12:37 pm

All they did was change the geometry, not the rotating center. I think the liquid piston design gets a better burn as a result. This change also allowed them to go with static seals, vice the rotor wipers on the wankel. The other thing is the fluid flow management looks much more interesting, and to me, more gas turbine like. I am thinking of it in those terms, and feel some design seeds germinating in my mind in this regard to take it one step closer to turbine world.

Did you watch the tech videos? Both live action and the sim videos were interesting. They have also tested a diesel version, with no plugs. Seems that they are getting sufficient compression to pull that off.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

DeltaV
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Re: Stirling Engine Advance

Postby DeltaV » Fri Jun 17, 2016 3:48 pm

The big problem with most rotary engine/pump designs (including Wankel and related) is "line" seals, instead of the more desirable "area" seals.

The one thing reciprocating piston engines have going for them is the option of adding as many piston rings as needed to get compression.

There is nothing new about Stirling engines in cars (goes way back). With limited info available, it sounds like this guy is scavenging waste heat from the already efficient, constant rpm, generator-spinning Stirling, for thermoelectric supplementation.

ladajo
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Re: Stirling Engine Advance

Postby ladajo » Fri Jun 17, 2016 4:11 pm

The big problem with most rotary engine/pump designs (including Wankel and related) is "line" seals, instead of the more desirable "area" seals.

The one thing reciprocating piston engines have going for them is the option of adding as many piston rings as needed to get compression.


And this is where I think Liquid Piston has cracked the nut, so to speak. By redesigning the rotor and chamber, they can now add fixed position seals to gain on compression as well, just like piston rings, except they are part of the 'cylinder' wall, vice riding on the 'piston'. Very clever.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

Tom Ligon
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Re: Stirling Engine Advance

Postby Tom Ligon » Fri Jun 17, 2016 4:24 pm

DeltaV wrote:There is nothing new about Stirling engines in cars (goes way back). With limited info available, it sounds like this guy is scavenging waste heat from the already efficient, constant rpm, generator-spinning Stirling, for thermoelectric supplementation.


I uncovered a problem with using thermoelectric devices this way while working on a Peltier cooler design this week. I was thinking of using a Peltier device for both heating and cooling, using a PID controller, but then I started thinking about the structure of these things and realized they are probably inherently sensitive to thermal fatigue. I looked it up, and they are. With severe thermal gradients applied, MTBF runs from a few thousand to a few tens of thousands of cycles, and even with 30-second cycle time on a pulsed-output temperature controller, life expectancy would be low, maybe a day or two. With devices of this sort used as a TEG, on a cylinder with reversing heat flow, TEG life might be down in the minutes.

You need a steady gradient across these things to achieve long life.

http://www.sscooling.com/thermoelectric ... -2-2-2-2-2

ladajo
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Re: Stirling Engine Advance

Postby ladajo » Fri Jun 17, 2016 4:39 pm

I have seen the ones used in camping stoves to provide auxillary power for charging. I wonder how long they last given the heating cycles from normal stove use?

http://www.bioliteenergy.com/products/biolite-campstove

Thanks Tom.
The development of atomic power, though it could confer unimaginable blessings on mankind, is something that is dreaded by the owners of coal mines and oil wells. (Hazlitt)

What I want to do is to look up C. . . . I call him the Forgotten Man. (Sumner)

DeltaV
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Re: Stirling Engine Advance

Postby DeltaV » Sat Jun 18, 2016 4:34 am

ladajo wrote:And this is where I think Liquid Piston has cracked the nut, so to speak. By redesigning the rotor and chamber, they can now add fixed position seals to gain on compression as well, just like piston rings, except they are part of the 'cylinder' wall, vice riding on the 'piston'. Very clever.

But the Wankel's epitrochoidal geometry still restricts seal placement to the "cusps".

A spherical geometry lets you spread out the sealing surfaces, e.g. --

Image

But spherical does not, by itself, rule out line seals, e.g. --

Image
Last edited by DeltaV on Sat Jun 18, 2016 4:58 am, edited 1 time in total.


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