Converting Compressor to an Alpha Stirling Engine

[gui_amuchastegui]

I bought a used twin cylinder to convert it into an Alpha Stirling Engine:

Figure 1 - whole compressor assembly

I removed the air intake filter of the both cylinder tapping the whole with a plug, and also installed a copper tube between the 02 air exit, as shown below:

Figura 2 - details of the modification done

Figure 3 - installation of the copper tube between 02 air exit


I didn’t want to make a lot of modification in the first run, so I didn’t install a regenerator and I made the cooler as simple as possible as shown below:

Figure 4 – bend plate to put some ice in the top


It is important to say that I didn’t open the cylinder so far to check the dimension, phase angle and everything like that. I know that is important, although from what I search, once I open the cylinder I will have to change the sealing gasket ($$), and I am trying to spend the less I can. Once again, I wanted to make a first try before going deeper in the details.

I put heat with a torch in the hot cylinder and ice in the cooler, as shown below:

Figura 5 - first test

I kept putting heat in the hot cylinder for more than 10 minutes and also trying to rotate the wheel hoping the engine would run. The temperature reach more than 200ºC in the hot cylinder and less than 40ºC in the cold cylinder (it was measured with a pyrometer).
Unfortunately nothing happened, actually in some point of the test the piston stuck in one position, probably because of the dilatation of the rings or piston.
In that time, I stopped doing the test and search for improvements that can be done in the engine.
I am going to list everything I am planning to do, and I would like to know if you guys have more ideas or can give me any direction to make this Alfa Stirling Engine runs.
1) Disassemble the engine to check the piston diameter, volume, phase angle and dead volumes.
2) Improve the friction of the engine:
a. There is a lot of friction in the engine, and I will check and possibly change the bearings, change the rings (I don’t know what type of rings would be better to install in that case)
3) Heater:
a. I know I have to install a heater, although I don’t know how can I design it.
b. Do you guys have any guide that could help me to design that?
I tried to reach any other work done related to converting air compressor to Stirling Engine. I found some jobs done in that area, although I didn’t see any one them with success. Do you guys see any problem or limitation by trying to convert a compressor in a Stirling Engine?
Any other ideas to improve this engine?
Best regards,

[Ian S C]

Gui, you have a good bit of work to do before it is even possible to get it to work. First the pison rings will be exerting too much pressure on the cylinder walls, but there is one important thing , and that is to remove the cylinder head from the hot cylinder and make an extended Stainless steel hot cap, the make a Heylandt Crown to fit on top of the piston. The pistons should be cast iron, with rings made of Teflon. You really need a new crankshaft with ball bearings on the main and big end bearings.
Ian S C

[cbstirling2]

Has anyone any where actually been successful in converting an air compressor to a Stirling engine??

[Alfista]

It is possible, there are examples, but it would be an easier conversion to a bash valve steam engine or even to an internal combustion engine.

[Ian S C]

Put V-twin compressor pump in the search box, and go right back to (12)2010.
A university in UK also tried to build one.
Ian S C

[cbstirling2]

I could only find one that was barely based off a Chrysler AC compressor. They had to rework so much, that they could have easily started from scratch.

[Ian S C]

Did you go to page 12?
Ian S C

[gui_amuchastegui]

We opened the compressor, and here is what we found:


Figure 6 - compressor head
The image above shows the 2 existents valves in the compressor head, that is useful for its works.
• Valves 1 allows the air flows inside the cylinder.
• Vales 2 allows the air flows outside the cylinder.
Considering that Stirling engine requires a closed circuit, we removed the valve 2 to allows the connection between the 2 cameras.

Figure 7 - valve 2 removed
We also measured the volumes of the cameras:

Figure 8 - image of the piston inside the cylinder

The results are below:
• Angle phase – 90º
• Piston Diameter – 63mm
• Lower Point – 66mm
• Upper Point – 0mm
• Cylinder Volume – 205738,2mm³ (205,7cm³)
• Dead Volume – 22,1cm³
Cupper Tube Length – 220mm
Cupper Tube Diameter – 9,525mm
L Connection Length – 90mm
L Connection Diameter – 9,525mm

The following considerations were made to take the decision if the Stirling Engine would be continued using the engine compressor:
• High Friction
The design of the crank shaft considers 2 bearing installed in just one side of the engine. That creates a bending moment, increasing the force reaction in the crank shaft, and therefore the friction.
o Piston rings – there is no piston rings or sealing, and that can possibly increase the friction.

Finally, I came to the conclusion that the engine has too much friction, and I am working on the design of a new Stirling Engine from scratch.

[tonyanderson]

I am currently building a sterling engine based on a Clarke V twin compressor

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[tonyanderson]

This drawing may be of interest

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[Tom Booth]

I am currently building a sterling engine based on a Clarke V twin compressor

That was the first type Stirling.engine I ever thought I might be able to build. Having previously seen some old V type compressor on an old commercial refrigerator before I knew what a Stirling engine was.

But then, when I thought about converting one I couldn't locate one anywhere. Not as scrap free for the taking anyway

Now 20 years or so later, I see they can be had brand new from various places like Harbor Freight or Tractor Supply, Home Depot etc.rather cheap, as replacement heads for shop compressors. From about $100 for 3 horse power and $200 for 5 HP.

Don't know about the quality, but if it could be easily converted to a Stirling engine, it seems worth buying one.

Over time my idea became to get two and run an actual air compressor with the Stirling engine using the heat of compression as a heat source to run the Stirling engine and cooling by Air Cycle Refrigeration to cool the Stirling.

Excerpt from: http://www.douglas-self.com/MUSEUM/POWE ... irfrig.htm

COLD-AIR REFRIGERATION

It is not possible to make a vapour-compression refrigerator using air because air cannot be liquefied at any reasonable temperature and pressure. (The conditions are quite different in machines specifically dsigned to liquify air) Therefore little or no reduction in temperature occurs on passing compressed air through a throttling valve. Instead work must be removed from the compressed air by making it drive a reciprocating engine or turbine. The use of an expanding engine is not merely a cunning way to reduce the power required to drive the process; it is essential for it to work at all. The work from the engine is used to help drive the compressor, improving the efficiency, but an air refrigerator can never be as efficent as vapour-compression refrigerator; it may not be 1/10 as efficient. Refrigeration engineers prefer to talk in terms of Coefficent Of Performance (COP) rather than efficency because it often comes out as greater than unity, and 'efficencies' of better than 100% have a long and dishonourable association with perpetual-motion nutcases

.

"Remove WORK from the compressed air" ? To produce refrigeration?

Huh?

I guess I'm guilty of being a "perpetual motion nutcase"

Because, air refrigeration requires a load to "convert heat into work".

So, typically with air-cycle refrigeration the cold is produced by using the compressed air from the air compressor to drive the air compressor itself to compress the air, which reduces the load on the compressor.making the compression much easier and more efficient. This is called "bootstrapping".

As the intent of refrigeration is to make cold, all the heat generated by the process is thrown away. Just like a modern refrigerator.

All that heat pouring off the back of millions of household refrigerators. Makes me wonder. There oughta be a better way.

The cold produced by an air-cycle refrigerator can be extreme. One reason they aren't practical. The air gets much too cold for ordinary household use. They are still used for flash freezing and Cryogenics.

So in theory, the Stirling engine could be bootstrapped by the air cycle refrigerator, not only mechanically but also thermally.

The extreme cold from the air cycle cryo-cooler would allow the Stirling to utilize ambient heat, as well as the heat from compressing the air.

Sounds crazy, perhaps. But Nicola Tesla put forward the same scheme around 1890 and published an article on his "self acting engine" in 1900.

He worked on actually building it for years but never succeeded and finally gave up I guess, but continued to believe it could work until the day he died.

Many of his inventions were just spinoffs, components of that one grand project to get "free energy" from the thin air.

He actually considered it a way to harness solar energy, not "perpetual motion". A way to just wring the solar heat out of the air for mechanical power or to run a generator.

Having studied it, I can't really understand why it wouldn't work, though putting it all together would be quite a feat of engineering.

[tonyanderson]

Well, finally got round to testing it at last and it did very nearly run un-assisted. I was spinning it it up with a drill on the crankshaft bolt and using plenty of heat, the tubes glowing red near the top. This was at atmospheric, the strange thing was that it seemed to be more reluctant to run on it's own when pressurized to 1 bar. Not what I expected.
Any ideas?

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[staska]

Please provide you geometry data - will make some simulation run for you.

Btw thsi guy was able to make it. https://m.youtube.com/channel/UCe3fCFq8H2cVzbVA-_lzO6Q

[tonyanderson]

Many thanks Staska,
Bore 63.5mm
Stroke 45mm
Swept volume about 200cc
Dead volume about 220cc
Compression ratio about 1.6:1
Hot side about 700 Deg C cold side about 20 Deg C
Static torque required to turn crank 0.9Nm at stiffest point (this may be the problem?)
Most of the basic dimensions can be seen from the drawing in the earlier post.
Let me know if you need any more data.

[staska]

Heater cooler tube length, diameter internal and numbers. Regenerator size and fill..