Author Topic: V twin air compressor to Alpha Stirling engine conversion  (Read 30381 times)

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GoVertical

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V twin air compressor to Alpha Stirling engine conversion
« on: July 09, 2010, 11:13:30 AM »
I started a new project. I am trying to convert a V cylinder air compressor into a Alpha Stirling engine.
After taking the heads off and spinning it by hand and relating to videos I have seen of working engines there seems to be to  much friction caused by the piston rings.  The construction of all the compressor parts appear to be Iron, including the pistons.  I have to open the crank case to see if the bushing can be replaced with sealed bearings, maybe that will help reduce the friction.  Over coming the friction caused by the piston rings seem to be the biggest problem. Any ways getting the compressor out of the box is always a good start.    



« Last Edit: July 09, 2010, 11:20:18 AM by GoVertical »
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GoVertical

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Re: V twin air compressor to Alpha Stirling engine conversion: Update
« Reply #1 on: July 09, 2010, 08:32:21 PM »
Before removing the heads and removing the crank shaft I noticed a lot of air entering and existing the crank case when I was spinning it by hand. There is a lot of back pressure caused by the pistons.  I am going to try to replace all the bearings with sealed bearings and leave the crank case open. This should remove some of drag and maybe the it will run using dry lubricate and the original Piston rings.
   The cylinder heads have two ports. Both can be used to pass the gas between the cylinders. Using a dual regenerator configuration should reduce drag and may help the Stirling cycle. I always enjoy taking stuff apart. I hope I can find the time to put this one back together. Cheers
 


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« Last Edit: July 09, 2010, 08:35:51 PM by GoVertical »
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GoVertical

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V twin air compressor to Alpha Stirling engine conversion: Up date
« Reply #2 on: July 10, 2010, 01:06:35 PM »
Completed disassembly of air compressor for Alpha Stirling conversion.

Removing the large bearing from the crank shaft proofed to be very difficult. After the three jawed gear puller was in place I almost snapped the box end wrench trying to remove the bearing.  I tried to heat the center of the bearing using the Sun and a magnifying glass. It did not work.  It required a couple of good hits with Thor's magic hammer aka "the SLEGDE" on the end of the gear puller to get the bearing to move. I should be able to replace the crank shaft bearings with sealed bearings.  Unfortunately,  there is no way to add sealed bearing to the piston push rods. But there are groves that can be filled with dry lubricate when it is time to reassemble.  The cylinder heads and reed plates can be hollowed out so heating and cooling tubes can be added to the hot and cold cylinders. I feel the piston rings add to much friction, so I have decided to try the high temp epoxy and dry lubricate piston ring idea.  I will need to fabricate a mold to add the epoxy to the pistons, then grooves can be added to the epoxy and filled with dry lubricate.   




« Last Edit: July 10, 2010, 01:09:56 PM by GoVertical »
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GoVertical

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Update: V twin air compressor to Alpha Stirling engine conversion
« Reply #3 on: July 11, 2010, 02:04:12 AM »
Completed concept drawing of Reed Plate and Cylinder Head modifications.  Removing un wanted material from the Reed Plate and Cylinder Head will allow for installation of heating and cooling tubes. Displacers can also be added to the tops of the pistons. As always making the concept drawings is the easiest part. Know the real fun begins, fabrication. At the very least it is a opportunity to improve my machining skills. Cheers
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Ungrounded Lightning Rod

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Re: V twin air compressor to Alpha Stirling engine conversion: Update
« Reply #4 on: July 12, 2010, 04:18:32 PM »
I like the idea of using a V-twin compressor for the foundation of a stirling.  B-)

If the rings have a lot of friction perhaps they aren't properly lubricated after the compressor sat around a while.  There should be little friction there or the compressor would have burnt out, much like an engine with a bum oil pump or low oil.

How hot will you be running it at the piston level?  Can you get away with replacing the rings with something like delrin?

Before removing the heads and removing the crank shaft I noticed a lot of air entering and existing the crank case when I was spinning it by hand. There is a lot of back pressure caused by the pistons.

I think that, when it's running as a compressor, that air acts as a "spring" to store power in the down part of the cycle to help on the up part.  This evens out the load on the motor.  Your stirling will probably not be self-starting if the crankcase remains sealed.  If you vent it, be sure to minimize the airflow restriction, which would be a power loss.  Beware of evaporating out any lubrication with that air.

Quote
  I am going to try to replace all the bearings with sealed bearings and leave the crank case open. This should remove some of drag and maybe the it will run using dry lubricate and the original Piston rings.

Quote
The cylinder heads have two ports. Both can be used to pass the gas between the cylinders. Using a dual regenerator configuration should reduce drag and may help the Stirling cycle.

Or just hook 'em to a common regenerator.

You could also put in an extension on the cylinder with a big port.  (You'll probably have to put an extension on the displacer cylinder anyhow.)

GoVertical

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Re: V twin air compressor to Alpha Stirling engine conversion
« Reply #5 on: July 13, 2010, 03:11:54 PM »
Greetings, the air compressor is new out of box. Thanks for pointing out that the rings should be lubricated.  I have seen two types of design, one with a closed crank case using oil in the crank case and one with a open crank case using sealed bearing on the crank and piston push rods.  The Philips Stirling engine used a closed crank case with oil.  This approach is the easiest to fabricate but I am concerned about blow by. I have read that hot O2 can mix with oil and explode.  They used a condenser chamber on the cold side of the engine to collect any blow by  oil and moisture  that may pass the piston rings. I plan on added a pressure relieve valve from a hot water tank rated at 150 psi to try to avoid any problems. The air compressor has a pressure release valve for the crank case and if the sealed area above the piston is at a higher pressure than the crank case apparently it increases torque and may aid in keeping oil from entering the area above the piston. This project is a first attempt and I plan on proceeding making the modifications for the hot and cold cylinder heads with the closed crank case just to see if it will operate, I can always make changes at a later date. Thanks again. Best regards. All comments welcome.
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harley1782000

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Re: V twin air compressor to Alpha Stirling engine conversion
« Reply #6 on: January 09, 2011, 07:01:50 PM »
Kind of curious if you have gotten any farther on your project???  Really interested in seeing if it works.

Jim

tanner0441

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Re: V twin air compressor to Alpha Stirling engine conversion
« Reply #7 on: January 10, 2011, 05:37:54 PM »
Hi

For the conrod bearings look at jet ski engines they use caged needle bearings on the crank and piston ends. On all the engines I have worked on they have always been very easy to turn by hand.  Probably be the same on snow mobiles.

You could try lubricating the bores with spray PTFE...

Brian.