V-twin compressor pump...

[vile_fly]

Well, the alpha engine has a 2:1 compression ratio I intend to take advantage of for the purpose of improved heat rejection. Any dead space thwarts that. The compression ratio will not be temperature dependent, like in the case of the beta engine. All the other alpha designs do the same thing. In the case of the beta engine, dead air space won't make too much difference because it has a 1:1 compression ratio that is dependent on the heat rise. I will be playing with several cylinder head designs, and will try this out just in case NASA is wrong.(it could happen) This will probably stir up a ton of debate, but I think I got the alpha engine figured out. You would probably lose me on the gamma design completely, Ian. I haven't built too many stirling engines, and it shows.

[vile_fly]

Found a solution in the hardware store while I got out of the house and all the savage tubing in it.
Here's a link to the screen shot. Teflon and graphite valve packing. Found in the plumbing section and it was cheap.
Now, my pistons need not worry about sealing. Ha.

The size "2-151" PTFE O-rings I had bought earlier barely fit right and were a smidge to big. The next size down would be way worse a fit, so I was stuck for a while. Then I realized I was an idiot. If the oem piston rings can run the end gaps......so can these ridgid ptfe rings. I just have to cut them, and use the rope packing on the top ring land.

[vile_fly]

So now, I need not worry about piston rings...the the 3/32" width of the rope seal is a perfect fit. I just had to run it around the ring land twice. Up front is the 2-151 ptfe o-ring in question.
Ah. forgot to post the link to the ptfe and graphite seal packing.
http://www.hardwareandtools.com/Danco-8 ... 61367.html

[vile_fly]

Now, I will show you what most of you already know. Ring sealing is not merely a function of ring material and the land width, but deals with where the gas will go. A top compression ring has a bevel on the top INNER part of the ring. This allows gas pressure to that normally pushes the ring down to get behind the ring so the it can push outward on that ring as well. This promotes a good seal when positive pressure is at the top. I know, your thinking that you can't use piston rings in a small stirling engine, and I agree. But this is not a small engine.

Drilling gas ports in the top of the piston just behind the ring land promotes an even tighter seal. This is how nitromethane dragster engines keep such high combustion pressure sealed in the engines. This can also cause excessive wear on that ring, but it is very effective. This trick is used to keep low-drag sealing rings to seal even when at higher pressures. If I have sealing issues, I will implement this design modification. The stiff ptfe rings I bought should handle this just fine.

[jaket]

hi, I'm new here, but i have been following stirling engine designs.

so little comment on this V kompressor idea. First of all when I first saw it, i thought this is just how it should be done. it looks so engine like. but after some thinking my thoughs are that if it would run, the output would be really slow. and i almost doubt that can it run at all.

if you consider the cylinder volume, I considered it to be ~close to soda can volume. I took a soda can and taped a plastic clear bag over the opening to see how much air is expanded when the can is heated with flame. the air expansion is very small, plus it heats slowly as the can is so big. you could measure the pressure generated by the heating and see how much pressure(from compressor) is needed to rotate this kind of engine. I doubt it is not enough.

if you compare this to other working stirlings, they usually use soda can size where the displacer moves and power cylinder is a lot smaller as the air volume change is so small that it needs a small piston to take advantage from it.

I surely hope this kind of build could work and make usable power, but at this point i cannot see it.


JT

[bowie]

Fly, thanks a ton for that Danco link, that was exactly what i was looking for and its so cheap compared to mcmaster. You really machine well, I wish I had that kind of skill.

[vile_fly]

Oh, I am a lousey machinist....no doubt about it. But flies are great scavengers. Heh. A thread should be started on scrounging parts so we can exchange our parts supplies.

[bowie]

Oh, I am a lousey machinist....no doubt about it. But flies are great scavengers. Heh. A thread should be started on scrounging parts so we can exchange our parts supplies.

Well, you're a good at both and I agree, a parts list is a good idea. I have my mcmaster lists up to this point.

I am taking the next 3 days to learn how to flux core weld so i can finish the displacer and housing cylinder. I like to build as I go. Actually 90% of the work so far has been done with a simple dremel. I am pretty excited about building some welding skills though.

So far this is what I have:

new001.JPG (119.03 KiB) Viewed 8446 times

-The regenerator is a modified inline fuel filter with 6 copper microchannels filled with stainless steel wool. Tubing is high temp reinforced silicone. The bottom of the regenerator has a flat face to mate with a waterblock that will be powered via waste heat (explained below)

-Cold side heatsink is a modified cpu fan modified with a copper heatsink that nests inside the cold cylinder head and sealed with a carbon buna-N gasket. The fan on the heatsink will be powered by waste heat collection via DC peltier tec modules.

My heat source is a rocket stove with a special flue that will accomodate the heating cylinder. The added bonus is that I can still use propane as well through the wood feed. At the top of the rocket stove will be a peltier tec generator that supplies DC to the powered waterblock and cold side heatsink fan.

-The Displacer is a 2"OD x 1.87" ID stainless steel tube, filled with stainless steel wool around a spacer that nests on a 1/4" threaded rod that will screw into a threaded bore in the piston. I havent cut it yet. In that pic, I put the tube into the bore just to get a sense of form.

Still left to do: connect displacers to existing pistons, stainless steel wool, fabricate displacer housing cylinder.

I have an axial flux alternator waiting for install if everything works out. It weighs within 3 oz of the orig flywheel.

PS. Where is Dave? He started this thread but disappeared? We would love to see how far you've gotten!

[jaket]

looks impressive, so you have displacers in both cylinders?

I think this method to attach the hose is better than that german industrial stirling(picture couple of pages back). as here the tube is connected below the dispacer, so any air travelling has to go past the displacer. in cold cylinder this already cools the air and in hot it reheats the air. I think it should works as inbuild regenerator.

I think the power of this engine http://www.youtube.com/watch?v=5pdqDQwe ... ure=relmfu is result of this inbuild regeneration, as the air has to go past the displacer to the top of the cylinder, but in this it only happens in hot cylinder, so if it happens in both cylinders, it should be more efficient.

I think the displacers should have quite close tolerance to the cylinders as any extra air space acts as a airspring preventing the pressure from getting higher. the less unnecessary air space, the less pressure buildup is lost.

I hope the silicon connection tube is not too flexy. hard tube plumming with copper or other metal tube could be better, as it doesn't expand or contract.

I think it would be nice to have pressure gauge to see what kind of pressure is building up when it's heated.

JT

[jaket]

http://journals.tubitak.gov.tr/engineer ... -98073.pdf

found this great article/testing stydy of similar engine. they got it running, but power was quite low.

great testing data anyway about working pressure efects and design points.

[vile_fly]

As mentioned in my previous post, the stroke on the research paper engine is too long to develop any decent RPM performance in my opinion. As you will observe, the regenerator is too small. Using the surface area of the displacer piston is effective.....for a heater or cooler, but is nonfunctional as a regenerator. No heat is actually stored without a decent regenerator that has no thermal short circuits.....hence the plastic or stainless tubing leading up to it.

Engineers miss the obvious many times in my experience....such as using two different sized wires leading to a fuel injector when we all know current is constant in a series circuit. This screw-up made it to production for 5 years. What a waste of copper. I can cite hundreds of other examples if you like.

[Ian S C]

vile fly, I agree about the design of the research engine, They need to halve the stroke, if they want some revs out of it, I find that the highest power out put is usually at about half of the free running maximum speed of the motor. I have fairly simple/crude equipment for measuring torque and rpm, but no means of measuring temperature. With atmopheric pressure motors I think barometric pressure is worth taking into account.
I see that they realised that both sides of the engine should be pressurised, it would be interesting to see the results of testing a modified motor, same capacity,ie., larger bore shorter stroke, and pressure equalisation. Same heating and cooling, same gas,etc,etc, I think the figures might be quite different. Ian S C

[vile_fly]

Well, it looks like a change of plan for the heater tubing. More like change of flare. Sorry guys, I have to use a true ISO bubble flare that is flattened out a bit so that it will seal better and be less sensitive to changes in angular contact. This thwarts my universal compatibility plan. The flattened bubble flare is formed by my expensive Mastercool flaring tool when use it at maximum hydraulic force.
I have some work to redo, it seems.
In the meantime, I have obtained an automotive a/c evaporator core for my cooling system. Sure, it's big....that's to insure I remove all the heat I can. If it is too much, I will switch to a regular heater core that I have.

flare change2.JPG (119.92 KiB) Viewed 8367 times

[Ian S C]

Another heat exchanger/ radiator is the unit from a car heater, or one of our lads uses a VW oil cooler. I'v got a couple of units out of domestic air conditioners. Ian S C

[vile_fly]

BAH! More delays!
My chinese mini-lathe has blunted alot of my cutting tools because I overworked it a bit. Basically, it loosened up on me. Now, I have to take it all apart and re-zero every adjustment there is so that I can have my sanity back. I will probably take the time to improve a few things on it while it is torn down. So, that has to take priority over the stirling engine. I also have to fabricate more cutting tools, also. It is also time for me to start mowing the lawn every week, so that cuts into my time and energy. Maybe if I try a little agent orange, I won't have to worry about the wretched lawn ever again.
My mini-mill machine time has been momentarily taken up by a fuel injection adapter project. It is now done, and I can continue with the stirling engine.....I hope.
The other obstacle is the relentless flow of estrogen from my girlfriend. She's always been jealous of my machines, and conspires to stop my evil plans of world conquest with this engine. "What? You? Sex? Now? Oh, no.....not agaIn! Ack! No, I will not put that silly thing on! Augh! Stop biting me! You degenerate savage! You'll pay for this!" (another tool blunts itself on the lathe during all of this)