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You have to respect what Koichi did. He pushed the envelope of what was considered acceptable. It just needs to be pushed even further IMO.

I should really take a month off work(in my dreams lol) and get some of these projects done. And speaking of projects....

I still have plans for a true 55 gallon engine build. Only now I am plotting a much lower temperature design in an alpha configuration. Just for fun, here is a teaser pic of another engine I am slowly working on. It uses two 30 gallon drums as the power pistons and is loosely based on a rider alpha design. It stands roughly 8 feet tall and has a bore of 19" and a stroke of 14". It's operation will be based on that of a gravity bong. Google that if you don't know lol... 2 55 gallon drums will serve as the hot and cold cylinders. Pvc pipe will communicate air between cylinders. Heating and cooling of the gas will be aided by the open water and the full surface of the 30 gallon drums. It's constructed of recycled automotive and tractor parts. The wooden frame was just easy and fast, long term plans would use concrete. It can be scaled up almost endlessly and requires no real machining. 2 feet of water head will limit internal pressure to 2psi, so it will be low compression and slow moving.

VincentG wrote: ↑Sun Apr 07, 2024 11:01 am
I still have plans for a true 55 gallon engine build. Only now I am plotting a much lower temperature design in an alpha configuration...It's operation will be based on that of a gravity bong...

One of these on steroids ???


which goes waaaay back, per


Note Peter Tailer credit (the thermal lag guy) back in 1990 (Scientific American). Beware that this basic scheme has some hidden issues as Bumpkin pointed out awhile back, somewhere.

Jeez, I had to dig deep for these...lol

Good stuff Matt, I was not aware of this patent. I tried searching for similar designs, but I didn't even know what to call it.

I thought about building a small model, but two things stopped me.

1: I'll be limiting my tinkering time with small "toys" until the weather gets cold again. I'll focus on large scale engines until then.
2: This design does not lend itself well to small models. With about .5psi from 1ft of water head, a small model just isn't tall enough.

hi,
i built a sodacan version in the 1990ties.
without a drain. result: condensed water in the connecting tube. bubbling noise after few minutes, and stop running after ¼ of an hour. so, the drain is the most important detail in this design.
regards, michael

Thanks for posting Waldschrat. I was a bit concerned about that but I'm hoping the large air flow will take care of any issues. I'd like to avoid a drain as I'd like to fill system with monophonic gas for very low temperature performance.

Don't suppose you have any pictures? How did it run? What temperature diffential?

1" of XPS insulation below the heat plate. Still have to source thin closed cell foam insulation to line the inside of the drum with.

The foam ring extends just above the heat exchanger and will seal against the bottom of the displacer when needed.

What's the water temperature ? I don't remember if you mentioned this earlier in thread.

Nothing set in stone at this point. Probably around domestic hot water temperatures near 200 degrees.

Added silicone sealant between the bottom insulation and the concrete to prevent air from getting cooled down between the two.
Also attached the displacer contact ring with silicone. I decided to leave the pockets going down around the hot water pipes open to get some extra heat exchanger area and hot reservoir volume. I did however add aluminum can as a radiant barrier to the concrete.
Welded stainless studs to the pipe flanges.
Ready for the heat exchanger.
At this point I think initial testing will be done with no cold end so I can get some early data open and closed cycle before I invest any more time and money building another heat exchanger. Looking forward to testing adiabatic expansion with an insulated "cold end".

Any suggestions or testing requests?

Do you have the power piston finished?

Are you still using a break diaphragm?

I have not done anything yet regarding the rotating assembly. I do still plan on using the brake diaphragm.

After assembling the heat exchanger in the chamber, I had a leak due to the test hole I forgot to weld lol. Ended up just welding stainless tubes to the bottom of the heat exchanger to greatly simplify the sealing process. Much less prone to failure like this. Fun fact of the day, this heat exchanger is made from an old NYC phone booth.


The top of the exchanger without mounting holes. Now it is just secured to the flanges with silicone. The water tubes will also be sealed to the pipe on the bottom of the chamber.

I think it's satisfying seeing one of the displacer discs laying on the bottom sealing ring and completely blocking off the heat exchanger.

Can't believe it's been almost 3 months since an update.

I've finished the chamber enough for some preliminary testing. The results, though on paper don't look great, are actually excellent. The first thing I did was let hot water(150F) from the kitchen sink run through the engine for about 20 minutes with the displacer elevated. This was to test how much heat is conducting through the body or the gas, and going on to raise the temperature of the chamber. The answer is essentially none. The chamber was only a few degrees higher than ambient surfaces in my sunny kitchen.
Then I tested to see how hot the surface of the heat exchanger was getting. 100 degrees F, but that can't be, so I painted the stainless steel surface with black primer and saw 135F. These thermal scanners are tricky and really can't be trusted for precise work at all, but good enough for now. Then I re-assembled and put ice on the top plate. There is so little thermal bridging that the ice froze to the top plate for some time. The surface of the top plate(tested both top and bottom) was about 30F. The walls of the chamber remained at about 80F.
The displacer travel was about 1.5" for this test, which is about 3200cc of swept volume. The actual volume is about 500cc more than that, until I put insulation on the chamber walls and fit the displacer to it.

In reality the area of the chamber walls is greater than the hot and cold plates, so they are acting to reduce the Tmax and Tmin by a large percentage. Figuring that the average Tmax is more like 105F, and the Tmin 60F, the expected pressure gain is just over 1psi. The uninsulated walls are likely bringing those temps even closer than that. This is evident by the fact the chamber does not go beyond a few degrees over ambient with the displacer elevated for extended periods. The thin steel walls of the chamber are enough to easily dissipate the heat moving through the gas.

I saw just over .25psi in testing. With well insulated chamber walls and a snug fitting displacer, I think this will rise significantly. Recall that an MEP of 2psi is my target for one horsepower at 600RPM. Refer to post 1 and 2 in the link to see how little pressure gain I believe is needed for decent power when the power piston is near or bigger than the displacer chamber. viewtopic.php?t=5638

I'm still looking for the right insulation for the inside of the chamber walls. It must be closed cell, smooth, and easy to work with. A roll of disposable coffee cup styrofoam is what I need. More updates to come.