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Converting Compressor to an Alpha Stirling Engine

Posted: Sun Feb 25, 2018 12:12 pm
by 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,

Re: Converting Compressor to an Alpha Stirling Engine

Posted: Mon Feb 26, 2018 1:46 am
by 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

Re: Converting Compressor to an Alpha Stirling Engine

Posted: Thu Mar 01, 2018 5:53 am
by cbstirling2
Has anyone any where actually been successful in converting an air compressor to a Stirling engine??

possible but not practical

Posted: Thu Mar 01, 2018 9:38 am
by 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.


Re: Converting Compressor to an Alpha Stirling Engine

Posted: Fri Mar 02, 2018 1:21 am
by 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

Re: Converting Compressor to an Alpha Stirling Engine

Posted: Mon Mar 05, 2018 1:51 pm
by 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.

Re: Converting Compressor to an Alpha Stirling Engine

Posted: Tue Mar 06, 2018 2:49 am
by Ian S C
Did you go to page 12?
Ian S C

Re: Converting Compressor to an Alpha Stirling Engine

Posted: Mon Mar 12, 2018 1:36 pm
by 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.