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Old 10-11-2018, 03:33 PM   #1
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Lots of interesting stuff on the forum lately about fuel cells, engine generators, silent IC engines, linear generators, etc.


The back of my mind has always bounced back to the linear generator concept as seeming to make sense. The "fuel" issues seen in fuel cell discussions lead to a why not the ability to use any heat generating source or fuel, which lead all the way back to the venerable Stirling heat engines.


Expanding the above, it then becomes a question of if you can take the rotating mechanisms out of a Stirling engine and make it a linear generator, and run it on anything from propane, gasoline, diesel, van waste heat, etc.


I have cast around in the past without a lot of decent information found, but I just ran across this Website page.


https://www.ohio.edu/mechanical/stir...ines/beta.html


As it turns out, the linear generator Stirling powered device has already been produced by some companies that are still in business.


The link above shows one and has lots of links to other websites of manufacturers that I haven't yet had a chance to look at closely or contact them.


There obviously have to be some reasons the principal hasn't been taken to more market yet, but it sure seems to fit the requirements extremely well. Simple, scaleable, any fuel, likely no temp restrictions, etc.


Los of reading to do, I think.


This is a 2011 article, so things could be a bit different by now.
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Old 10-11-2018, 04:00 PM   #2
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There's a Stirling engine on the RedHawk Energy site: Qnergy PowerGen Stirling Engine Generators - RedHawk Energy Systems, LLC

It looks too big. I'm not sure if the photos are of the 1.2kW or the 5.6kW model though.
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Old 10-11-2018, 04:14 PM   #3
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Yep, that looks like a Stirling linear generator. The links at the bottom of the page seem to say it is in the 3.8KW range, and don't indicate how much of that outside box is the natural gas handling stuff.


The original link mentioned units being made at as low a 35 watts. In the big picture of the "generate and store" crowd, that would give over 70AH per day and cover even most compressor frig users. That is 1/100th of the output of the 3.8KW unit, but the size certainly wouldn't reduce that much.


I think we are going to find more commercialized units than I originally expected, although they will likely be larger than many of us would need. Depending on the size of that 3.8KW actual generator, it would be a great one for the folks that need/want 24hr a day air conditioning.
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Old 10-13-2018, 09:42 PM   #4
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Interesting reading, thanks for the reference.
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Old 10-14-2018, 02:36 AM   #5
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In the beginning of this year I talked to CTO of Etagen, new company from Bay Area, as a result of free piston range extension email discussion with my friend in California. This is a very different thermodynamic cycle. http://www.etagen.com/technology/. I have no clue if downsizing of this technology is possible and if yes to what size.

Stirling cycle engine tend be much larger than comparable power IC engines, but they can be powered by practically anything.
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Old 10-14-2018, 02:45 AM   #6
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Quote:
Originally Posted by GeorgeRa View Post
In the beginning of this year I talked to CTO of Etagen, new company from Bay Area, as a result of free piston range extension email discussion with my friend in California. This is a very different thermodynamic cycle. http://www.etagen.com/technology/. I have no clue if downsizing of this technology is possible and if yes to what size.

Stirling cycle engine tend be much larger than comparable power IC engines, but they can be powered by practically anything.

Interesting stuff. "low temperature reaction between fuel and air" and "flameless" sounds like catalyst reaction to my non chemistry mind.


The Stirlings do likely have a size disadvantage, but in a linear it appears to less than in a rotational. The quieter, burn any fuel part is a huge advantage, though.
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Old 10-14-2018, 03:16 AM   #7
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Interesting stuff. "low temperature reaction between fuel and air" and "flameless" sounds like catalyst reaction to my non chemistry mind.


The Stirlings do likely have a size disadvantage, but in a linear it appears to less than in a rotational. The quieter, burn any fuel part is a huge advantage, though.
I am not sure about ignition and reaction, they are tight lip about it and I believe it is their core technology. Volume increase of reaction gases above water evaporation temperature is only 16% (C3H8 + 5O2 = 3CO2 + 4H2O > 6 moles to 7 moles/ Avogadro's law 22.4l/mole) Thermal gas expansion must play a big role. Reaction could start with laser pulses or catalytic. Time will tell about their success.

One of the major efficiency factors in free piston engine is elimination of piston side force resulting in dramatically reduce piston to cylinder friction. I still believe that free piston technology with prevail as electric cars range extenders, and perhaps some side migration to RV world could happen, unfortunately the RV small electric generator market is very small.
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Old 10-14-2018, 05:59 AM   #8
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The Stirling in the original link is a free piston generator in one of the examples, of course with external heat source. Marko's example is also, it appears.
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