free displacer beta

Discussion on Stirling or "hot air" engines (all types)
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fullofhotair
Posts: 265
Joined: Sun Aug 05, 2012 6:28 am

free displacer beta

Post by fullofhotair » Sat Sep 15, 2012 8:48 am

I was trying to think of a way to connect the displacer but keep a beta,with a diaphram power piston totally sealed.By being totally sealed you could use helium,there wouldnt be the friction of the rod rubbing on the seal etc.I looked at free piston engines.They time themselves.So why does the displacer even need to be connected? Couldnt a small spring on the hot end be used to return the displacer?What am I missing? Everybody wouldnt go to all the trouble of making seals and crankshafts if it wasnt necessary.

Longboy
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Location: Tucson, AZ

Re: free displacer beta

Post by Longboy » Sat Sep 15, 2012 10:43 am

Asked and answered by...."yourself"! However in relating a free piston design to a mechanically connected Beta might be your miss. Most would not consider it a troubleing feature, this pushrod through a gland method, if you end up with a tried and true running model. A somewhat hybrid free/mechanical Stirling design with this spring operating the displacer would most likely not be consistant in timing in the Stirling cycle for the following reasons: heat and friction. Heat being component failure of the spring and friction in the displacer interaction against the spring, the enemy of Stirling operation. Its a stretch for a modeler to gain benefits with an enclosed system using Helium.......the engineering costs of developing a Helium system best left to commecial intrests and this is why crankshafts are nessesary!

fullofhotair
Posts: 265
Joined: Sun Aug 05, 2012 6:28 am

Re: free displacer beta

Post by fullofhotair » Sat Sep 15, 2012 11:38 am

Longboy, thanks for the response. I understand the limitations of using metal springs how about an air spring? Can you think of a way to incorporate that? The reason I mentioned the helium was because Approtechie mentioned he was using helium in one of his engines. His engines are designed for thirdworld applications and are pretty basic. I dont remember him saying it did or didnt improve the preformance.

Ian S C
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Re: free displacer beta

Post by Ian S C » Sun Sep 16, 2012 2:41 am

A better idea for that sort of thing is more like a GAMMA motor, the displacer has a thick rod, not sure of the correct ratio for its diameter, but about 1/4 of the diameter of the displacer works for me, these are called Ringbom motors, one of the early ones that is well known is called Tapper, the powr piston is connected to a crank, and flywheel. At the moment I an working on a rebuild of another type similar, except that it has a heavy power piston supported by magnets (like poles repel), no crankshaft. The magnet attached to the piston passes through a coil ,and works as a linear alternator.
With your idea the displacer rod will have to pass through the diaphram, as it would through a piston, and both sides of the diaphram/piston are in the area requiring pressurisation. I think I'll have to stop and think about this. Ian S C

fullofhotair
Posts: 265
Joined: Sun Aug 05, 2012 6:28 am

Re: free displacer beta

Post by fullofhotair » Sun Sep 16, 2012 5:50 am

Thanks Ian, What I want to do is make a stirling engine that will run a small evaporative cooler.With my limited skill level I couldnt have hoped to do it till I saw Approtechies and Junkies engines on U-tube.These diaphram power piston engines seem to have enough power to move some air and still have enough left over to pump a little water over the aspen pad.I wanted to make the engine a little simpler by being able to eliminate the crankshaft and just use the flywheel to time the power piston.I looked at the Thumper and Ringbom.So the large rod in the displacer and the capped cylinder in the power piston work as an air shock. That should be something I could make.I could still keep the displacer doing double duty as a regenerator couldnt I ? Are there any reasons I shouldnt use this set up as compared to the attached displacer? Is the ringbom an inheritantly inferior engine?

Ian S C
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Location: New Zealand

Re: free displacer beta

Post by Ian S C » Sun Sep 16, 2012 11:48 pm

The displacer of a Ringbom motor is in the same propportions as the one on a BETA or GAMMA motor, the thick displacer rod is actually another piston that controls the movement of the displacer by the change in pressure created by the power piston. If you get it right, you might do as I did, Mk1 of my stove top fans was a Ringbom, and appart from a bit more noise, it was too powerfull for its perpose, the Mk2 vesion is a GAMMA motor, and much more sedate. Ian S C

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