Stirling cycle machines, appropriate technology and design ideas

[Tom Booth]

I've been seeing this curious engine for sale online a lot lately.

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Very inexpensive. It seems unusual in that it is a very simple bullet design, like a typical "thermoacoustic" or glass test tube type engine but with a stainless steel cylinder, so, presumably it should be able to take very high temperatures.

There is no displacer, just a power piston and (?) I don't know what's inside. A steel wool regenerator perhaps? Maybe a choke between the power piston and regenerator?

I tried pulling off the stainless steel nose as soon as I got it, but it wouldn't budge. Not sure if forcing it too hard would damage something so decided to try running it instead.

As I kind of suspected, it took a generous supply of heat to produce any signs of it wanting to run at all. A tea candle did nothing for it.

So I took it down to my workshop and gave it a blast with the propane torch.

It had quite a lot of compression. Even when cold this engine is unusually difficult to turn over due to the high compression. Glass piston and cylinder.

It pretty much took getting the cylinder glowing red hot with the torch to get the engine to run, but when it did finally run and get up to speed the torque was quite good in that I was able to apply some break to the flywheel and the engine could still run.

Anyway, it is so simple in construction and yet capable of handling extremely high temperatures, I thought it might be a good candidate for this radial engine running on a rocket stove chimney concept. The basic engine design that is. Even this exact model, if someone wanted to buy a half dozen or however many.

I have a feeling there might be some room for improvement as well but I think these engines would work.

The engine seems to run about the same regardless of where the flame is applied to the cylinder; middle or end, but seems to slightly favor the middle, but mostly just seems to love a lot of red hot heat.

Now that I know it will run, I'm still curious to see what's inside.

[Tom Booth]

Well, it came apart fairly easily after all. Just needed a bit more force.

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Pretty much what I thought, stainless steel wool in the nose:

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But a little unusual in that it is a very small little ball and completely jammed all the way down into the very end not closer in near the central orifice.

Forward side of orifice:

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Back, power cylinder side:

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[Tom Booth]

Flywheel and base removed, showing the basic simplicity of the engine:

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[Tom Booth]

Seems quite willing to run "free piston".

I have to say, it starts up much faster and runs with a lot less heat this way.

https://youtu.be/PEhvHg-Gruk

[matt brown]

So Matt, do you seriously believe putting two of these together and filling one with hot and the other with cold water would produce some sort of motor.

Definitely not DIY unless you have a Bill Gates bank account, however, it's worth studying (I can't find any grant meister action). At least it solves most of the classic HAE issues and the typical side seal issues that plague georotors (Wankel, StarRotor, et al).

https://pfspumps.com/blog/pros-and-cons ... ompressor/

Scroll down on this link to the pros & cons, especially noting:

isothermal LRP.png (21.33 KiB) Viewed 5326 times

I figured someone must have 'tried' this, so a quick patent check turned up US4984432A from 1991

https://patentimages.storage.googleapis ... 984432.pdf

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and thar she be...

15 yrs ago, I nearly bought a Hydrovane compressor to play with when the scrolls were gaining traction. If unfamiliar, google Hydrovane for another WTF moment. BTW the relatively massive motor on typical liquid ring pump is due to vacuum app where the effective COP is so nasty...like trying to suck chrome off a Harley (as the lab guys used to say).

[matt brown]

And let's not forget my favorite rotary engine aka the Elbow Engine...

https://www.youtube.com/watch?v=3eFmMi4eHCI

Smokey Yunick brought this 'water pump' back from obscurity in the early 1970s with the 10 cylinder 135 deg banked Oliver-Yunick steam engine (see Popular Science Dec. 1971)

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[Tom Booth]

Interesting patent. It claims it could work as an engine rather than a refrigeration device. I'm still skeptical, but I haven't given the patent a thorough reading so I don't understand how it is supposed to work as an engine even in theory at this point.

I came across this while browsing around:

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Michel Cam Engine: 1921

Image from this page: http://www.douglas-self.com/MUSEUM/POWE ... cam-IC.htm

This was a very real engine design and apparently had several advantages over a crank engine. Notably the rotating cam could have high torque by increasing the number of lobes working similar to gear reduction.

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https://oldmachinepress.com/2014/02/24/ ... l-engines/

[Tom Booth]

Another rather interesting attribute of this Michael engine is that it can be stacked.

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A Michel engine with four groups of three opposed-piston cylinders. This engine had a total of 12 cylinders

https://oldmachinepress.com/2014/02/24/ ... l-engines/

This engine however had three crankshafts rather than cams.

[matt brown]

Interesting patent. It claims it could work as an engine rather than a refrigeration device. I'm still skeptical, but I haven't given the patent a thorough reading so I don't understand how it is supposed to work as an engine even in theory at this point.

Most 'banked' rotary schemes are Brayton or Ericsson and liquid ring would be Ericsson. Just think of the liquid ring as common vane pump where a compressor pump and an expander pump are cross coupled thru a counter flow heatX. In this manner, there's no phasing issues, heatX has constant HP side and constant LP side, and the liquid rings supply heat source & sink. They have 10 bar liquid ring compressors already, so it does appear possible. What I'm suggesting is that this basic mech might be able to be further optimized for an engine. We live in an ICE piston world, so most guys are clueless how the common vane pump works. It's not enough to simply say that the segment volumes change...it's the pressure differential "across the vanes" that hides the magic. The fixed 'vanes' of the liquid ring pump might allow a more optimized 'vane' design than common blade style.

Once you discover the liquid ring pump, you have to ask, just who are all those georotor nut jobs trying to fool ???

[matt brown]

I came across this while browsing around:


Michel5 anim.gif


Michel Cam Engine: 1921

Image from this page: http://www.douglas-self.com/MUSEUM/POWE ... cam-IC.htm

This was a very real engine design and apparently had several advantages over a crank engine. Notably the rotating cam could have high torque by increasing the number of lobes working similar to gear reduction.

Hey, Vincent, there's your ring cam. Maybe more torque due to more power strokes per rpm, but sliding past those cam 'peaks' will be grossly inefficient (and quickly destroy cam). Most 'novelty' comes from a failure to fully understand many competing issues. Anything that slides sucks, just consider a Scotch Yoke vs common slider-crank.

[VincentG]

There ya go Matt. If we look to a mechanical diesel fuel injection pump we have cam driven pistons as well, either rotary(swash plate) or inline(camshaft). I guess you could seal long conrods that extend outside of the pump and operate pistons. They are capable of long maintenance free service life. Heck that's how a pressure washer works too...We would have to study the friction losses to efficiency gain vs. Slider crank. But my feeling is that it adds too much complexity to manufacturing in the diy setting. Are we still concerned about manufacturability? It's numero uno on my list.

Your mention of the gerotor pump has me thinking of the possibility of turning a twinscrew air compressor into an engine.

[matt brown]

https://www.youtube.com/watch?v=AWQCEppxRxk

This is my favorite HAE, the original Rider (SE alpha). These puppies have some unique features like the pistons 'rings' which are leather O-rings fixed atop each cylinder. This allows both cylinders ID to have an unmachined pipe finish vs both pistons OD which are machined (easier to machine an outer surface than an inner surface). My current project is upgrading this basic engine with some...slight of hand. It's amazing what you can overlook for years until the right 'altered state' kicks in...

[Kaoron]

I've been seeing this curious engine for sale online a lot lately.

Nice find! It looks a lot like what I had in mind trying to devise a list of supplies for a diy prototype. Basically I thought one could use CO2 canisters for the heating chamber, glass tube for the expansion chamber, epoxy putty piston, and a finned copper sleeve to act as a heat exchanger on the cold side.

[Tom Booth]

I was curious to see how the linkage might work with just an outer ring connecting the pistons together as originally proposed (without any cams or lobes).

I had some things left over from other projects that seemed like they might give a rough idea.

At first I tried just a direct connecting rod between piston and outer ring, but it became clear immediately that some kind of elbows would be needed.

Probably also some kind of guides or springs or something to keep things relatively centered and in position, but overall, it seems like it could work.

I'm thinking that some kind of common connection joining the pistons together would help smooth out the often erratic behavior of the "free piston" type engine.


https://youtu.be/UtvSLHjf2tw

[Tom Booth]

Not sure how the video went sideways, but I like it better this way:


https://youtu.be/KLRaDSJoRfs