I give up

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I give up

Postby brian_clayton2000 » Thu Nov 06, 2008 8:01 pm

I see lots of explanations and reasons why a larger Stirling is not
efficient, would be too large, too expensive, etc...

But I see no "failed" projects. No one horse stirlings the size of a
city bus.

But I do see interesting things, like the 5hp Stirling built in
Bangalore or something. I called sunpower by the way, they will
design and build and 5 hp or so Stirling for 12,000 to 14,000 dollars
or so.

After finally realizing success on my tin can sized Stirling, and
finding pretty much no information or large projects on the internet,
I decided to build one for myself. I might fail. It might not work.
Then at least everyone can have a picture of what will not work.

I already started. Scrounged up a very large acetylene tank out of
the barn behind the shop. Its about 14" in diameter, and stands about
5' high. Looks about right. Did I mention I am not and engineer?
Drained the rest of the gas out. Must have had a lot left in it, the
tank turned icy on the outside. I hope I didnt have a deposit on this.
Unscrewed the valve, it was easier than I thought it would be.
Filled the tank with water, hoping this would be the best way to purge
the rest of the gas. Turns out, when I cut the top of the tank with a
torch, it didnt blow up, so I guess it was. I cut the tank right
below the weld joint for the top of the tank, so now I have a long
cylinder with a nice bottom in it.

I want a wood fired deal, even though somebody said that would suck,
because...well, why not? So, after a great deal of thought, careful
planning, and engineering (about 5 minutes of sitting on my stool and
staring at it), I decided to cut a access door in the lowest part of
the side. Why? To get the ashes out of course! The hole is about 6"
by 6" and extends about to the middle of the tank bottom. Later I
will box it in with 1/4" plate and make a door. Lucky for me, the
bottom is welding in, and the joint leaves about a 1/4" or 3/16 lip on
the inside where the bottom slug is slid into the tank. Looks great
for holding a fire grate. So, I dug out a piece of walkway grating
left over from another project, and using the top I cut off for a
pattern, cut out a circle and trimmed it until it slid down the tank,
and sat on the lip. Oops, need a fire door.....cant get wood in
otherwise. No problem. Fire up the torch, careful measuring and
plotting.....nice square opening. Great, even if I stop now, I still
have made a really heavy duty fire barrel.

After some precision measuring with my craftsman tape measure, I
decided to make the displacer section 14" by 20" long, so that means I
need to cut a circle out of some plate and weld it in 20" from the
top. I should have some drop left, when I make the top plates, so
that can come later. After some careful deliberation, I decided top
make the displacer piston 13.5" long, and use 6" for stroke. Being
that I am really impatient, I wanted to get started on the displacer
cylinder. So, I cut out some 20 gauge steel with the plasma arc into
a strip 13.5" by 44". The length was figured 14" x pi, plus a little
extra. I thought the shop down the road had a roller, to form my
tube, but they couldnt do one that small. So, being that I am
impatient, I marked out 40 or so lines, one inch apart, and bent it
the the brake, each line about 10 degrees or so, to form a tube. It
doesnt look too bad, At first I wanted it too be smooth on the sides,
but now I think that the "bent" sides will add some strength to the
displacer piston. For the jig to weld the seam up, I think I will
take some plywood, and cut some 13 1/2" holes in it, and slide a few
over the tube, to keep it straight while I weld the side up. I
stopped fooling with it while I worked on another project in the shop
today, but I did decide to do a Scotch yoke drive (sort of), that I
think will be super easy to build. I did manage to bum some 12mm
chrome plated shaft material today, look like it will work great for
the displacer rod, and being ground rod that is triple plated (like
hydraulic cylinder rod), it should run smooth in a bushing and seal.
It came from some work that was done at a local papermill, some part
they replace every year. Something about coating on paper, I dont
know, I just know I have 10 foot of the stuff for free.

A few things I have decided, but may yet change.

I want a atmospheric pressure engine or one that can pressurize itself
with a onboard pump. (like the 5 hp deal)

I think I will make 2 power pistons/cylinders, pretty much just
because I have 2 short pieces of 3 1/2 DOM tubing that will work
great, and I dont have anything else handy that will work for a
cylinder. Well, I do have some leftover sleeves out of of the race
motors, they are a 4.125" bore, but the wall thickness is only about
.090 or so. But, I do have some pistons already that out fit them...
so who knows.

Water cooling? Very probably. I am just not going to bother with
making a water jacket until (if) I get it to run.

I decided on a variation on the scotch yoke, just because it fits into
my idea. After realizing a walking beam would be huge, I had thought
about a chain driven rhombic.....but the scotch yoke came to me in a
brainstorm this evening, so hey....sounds good to me.

Dont care how much it weighs
Dont care how big it is
Dont care if all it does is make enough power to run itself (it will
make a cool looking heater)

If you respond, please only helpful input. Lemme say this. I am
doing this for fun. Sitting in the same shop is a 2800 hp twin turbo
2005 mustang pro mod I built from scratch, I have a decent machine
shop. I am a competent fabricator. Part of my job is to piddle with
stuff like this. Wheeeeeeeeeeeeeee.........lets have some fun! I
will post some pics when I figure out how.
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Joined: Thu Nov 06, 2008 7:01 pm
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Last Name: clayton

Response to I give up

Postby bptdude___2569 » Thu Nov 06, 2008 11:04 pm

Your writing is wonderfully entertaining as well as actually detailed. It was like reading a project by Red Green!

OK, so, here is my constructive only tips, for whatever they are wortth.

1. # water jacket

Just believe me, if you want to try something that might work.
If you have neglected the cooling end, you will be trying to use only the hot end to move the displacer. To do this, you will need the heavy flywheel every thinks is required, to get past the dead stroke zone.

If you supply equal temperature difference, but drop the cooling end to a usable work supplying temperature, the displacer will be pulled on the cooling cycle, as well as pushed on the heating cycle.

So, find a giant stainless steel tank, from behind somebody else's barn, put it between your well and your pressured water tank, if such a thing is legal. No air need be in this tank. As you use water in the house, this tank will maintain lower temperature.

The cool end of the Striling is sealed into two holes cut with that handy torch into the stainless steel tank and the Stirling is stuffed through like a sausage.

When you run the Stirling in the moring, and everybody starts to take a shower and put the laundry on, the Stirling will gain more power, or maybe just run at all.

2 -

You forgot the regenerator. I'm the guy who keep pushing the theory that next generation Stirlings will have the regenerator removed, so please believe me when I say you should have one.

It will lower the required temperature difference but also, unknown to most, act as a preassure storage much like an inductor in the circuit. Ignoring that last sentence, most people would fill the middle of the tank with plain clean steel wool. Pull it apart very loose and stuff it in like attic insulation for almost the middle third of your tank, betweent the hot and cold end.

One bad effect of the regenerator is making the work capacity low, but you in your case, you don't care. Don't waste the power, you will get some.

If you forgo the water jacket, at least weld a collar of bizarrre looking window sized sheet of aluminum, mounted along the length of the cool end of the cylyder. Use a large fan made of a light piece of plexiglass, that will blow air over the cooling fins. This will be attached to the displacer, and if you are tricky may also act as a flywheel.

The displacer pushing the air over the cooling fins will increase the power of the engine, which then blows more air. The feedback cycle will limit out shortly, but still, every bit helps, and wouldn't that make the furnace even cooler looking?

If the fan sucks fresh air over the cooling and pushes it over the hot end, so as to push hot air into your house, it may slightly cut the power of the engine, but have a built-in blower fan for hot air distribution.


Best of luck.
We will see it on YouTube, right ?

- Joe McLean
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Response to I give up

Postby bptdude___2569 » Thu Nov 06, 2008 11:12 pm

I hate when I forget something.

So, how to you stuff steel wool in the center of the cylinder if your displace is there, moving back and forth?

Not sure, but maybe tighten the fit between the displacer and the walls without causing friction. This will actually make the cylinder ride better, ignoring the need for air passage for the Stirling process.

Instead, think maybe of this.
In the center of the displacer, cut a hole of some size you have to pick, and put the loose steel wool there, for a displacer. You will have to fool with displacer size, so be prepared. That will be the tweak thing to play with, to get the engine to move.

Best of wishes and luck.
Let us know, many of us wish we were as handy and destructive as you!


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Response to I give up

Postby bptdude___2569 » Thu Nov 06, 2008 11:28 pm

I just can't stop....
This is fun..

Now, I hope you really didn't cut the ash box and fire door in the hot end. If this thing is a Stirling, you need to keep the cylinder air tight.

You heat from the outside, as in you need to find an old wood stove, again cut a hole like you did for the water tank, and put the hot end of the sausage through the wood stove.

To be clever, and use one of my free design tips, do this. Drill as many holes as you can, without destroying the strength of the cylinder. Run re-rod, the stuff they use for concrete construction, through these holes. Maybe run the cylinder through the wood stove, THEN fill the holes, air tight with furnace epoxy, with the re-rod, so you can leave lots of re-rod hanging out on both sides. Obviously this is to speed heating .

And, for an advanced design tip, cut the tank in half, and epoxy in a ring of material, like stone, that transmits heat a lot less than the steel of the cylinder.

OK, OK, I'll stop for the night.
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Response to I give up

Postby brian_clayton2000 » Sat Nov 08, 2008 5:52 pm

Thanks for the CONSTRUCTIVE input Joe.

Lemme run over your responses, and that will sort of tell you where the project stands.

Water Jacket. I had already planned on a water jacket, I just had wanted to wait until the project was further along (as in turning over at least one time by itself) Basically, I has planned on "sleeving" the outside of the tank -lets say a 16" tube, split lengthways, fitted and the seams welded back up, giving about a 1" clearance around the inner cylinder. My problem is that I dont know if the cooling water will work better running the entire length of the displacer cylinder, or just to try to cool the "cold" side. Best I can gather, you only want to heat and cool the air moving the the engine, so I came up with a interesting Idea. Dont know if it will work, but its something to think about. Lets say a flat coil of 3/8 tubing, fixed to the top of the displacer cylinder. Thru this tubing, you run your cooling fluid. The tubing would be arranged to allow some airflow, but try to keep clearances to a minimum to reduce dead space. Now, coat the inside of the cylinder and the displacer with a insulating coating. (I have some thats like a thick paint, its used in very high temp, 1200+ f, applications in industrial applications, like the outside of boilers and calciners. It insulates very well for what it is. The heat exchanger is of course left unpainted. Although the cylinder walls would not be conducting heat away, they would also not be conducting heat into the air (in theory). The idea is that you would heat and cool only the air (Keeping heat transfer at a minimum). Just tossing it around....
Running spring water is a non issue.....spring behind the house puts out 58 degree water, at the rate of a million gallons a day. Right now it is set up to run a 16 foot high 2 foot wide waterwheel.

Regenerator. Dont know yet. I have been told that need one. I have looked at a million different Ideas. I really cant grasp the idea you are trying to tell me right now.....

Well, sort of...I understand the "tube thru displacer piston, steel wool" idea, just not the first one

Fire door/ash box. Dont worry, I cut out a disk to weld inside the tube to make a new bottom for the displacer cylinder, in fact I have already bent and started welding in the tubes for the heat exchanger. My best guess....I mean design. Picture this. 14" diameter about 4' tall tube standing upright. The first 3" or so the the ash area, followed by a grate. The next 20" is the fire box. This is followed by a plate welding in, containing my heat exchanger tubes, creating the new bottom of the displacer cylinder. This basically leaves me with a 14" x 20" displacer cylinder. On the very top I am making a flange, like a steam or water pipe, with a ring of bolts to bolt down a flat plate that will hold the crank, flywheel, power piston/cylinders, etc...

I have some picures, lemme see if I can post them here.

Thanks for all the help, and advice.

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Response to I give up

Postby brian_clayton2000 » Sat Nov 08, 2008 6:02 pm

I cant seem to post picures, but I stuck them on my MySpace page...look at album "Stirling project" http://www.myspace.com/mancomesaroundsoon
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Response to I give up

Postby bptdude___2569 » Sun Nov 09, 2008 5:40 am

Oh, you said such a nice thing about my silly attempts at ideas, and I can only imagine all the experts who told you a thousand reasons why you are not doing it right... Now I have to comment like that.

You last posting shows such skill, if anybody is going to build a cool homebrew Stirling, you certainly are on the list.

But .... that said... *cringes*

I saw the pics on your myspace, and I don't know what the heck you are building, but I do not see how this thing is even close to a Stirling.

A Stirling is an airtight container of gas that has hot on one end, cold on the other, and uses the expansion and compression of the gas in a back and forth occilating cycle to produce work.

Since you have already cut the tank, with a firebox on the bottom, all I can suggest is the following.

Get more cylinders of the same type, and they will be mounted to incrase the stack height. The height should be taller than your house for starters. Use a wind turbine up the center of the stack to take the moving exhaust heat to turn it.

Think of a way to get some of the mechanical energy OUTSIDE the stack. For your feedback loop, use some of that mechanical energy to blow air into the firebox, to make it as hot as a blast furnace and help push the air up the stack.

Hopefully the steel won't melt! :)

WARNING: keep this stack so far from anything that will catch fire, even if the stack tower falls over in any direction.

Use the remaining mechanical energy recovered to drive an air fan to blow how air off the stack into the hot air heating system of your barn or whatever.

You basically have invented a turbine hot air furnance that will heat tremendously more than a simple wood stove. There are other wood furnaces out there, but yours will require not electricity and burn hotter, though not sure how the efficiency will work. If you chop your own wood, who cares, really about that.

I may not understand what you are doing as far as Stirling, but please consider you may not understand the Stirling cycle.

# ya buddy, Joe
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Response to I give up

Postby bptdude___2569 » Sun Nov 09, 2008 5:58 am

I always think of something else, after I post things.

All this assumes a continuation of my previous post about turning your idea into a wood fired turbine.

OK, to extract the mechanical energy...
Up the stack you install a fan blade turbine, or even multiple on a center shaft running up the stack. Up past the top turbine, you simply have a mount for the shaft. Keep the weight as light as possible.

Run the shaft down through the firebox floor, into the ashbox. You may want to create a second chanber below the ashbox, it doesn't have to be tall. Down there you do two things.

1. Mount the other end of the shaft, of course, in a yoke that will allow it to spin still.

2. Get a motorcycle chain and sprocket, or something like that, to be able to take the shaft power outside to a mechanical device.

You can use the mehcanical energy to make electricity!

As a feedback loop, if you want to get fancy, use sheetmetal to go around the lower portion of the stack, open on the top and the bottom being the feed into the firebox for burning air. This will preheat the air to go up the stack. The Stirling brothers actually did something like this before they invented the Stirling engine.

If you ever built this, please put a video up on the web.
Be sure and record the sound!
*huge grins*

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Response to I give up

Postby bptdude___2569 » Sun Nov 09, 2008 6:01 am

and now we will have to end this thread, since we have diverged away from Stirling engine designs.

Unless you can convince people you really are building a Stirling.
We will get the "off topic" warning, which is fair.
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Response to I give up

Postby brian_clayton2000 » Sun Nov 09, 2008 7:52 am

Whoa cowboy......look at this. Simply one of those "hey, I can make that"
My idea is a little different, but the same basic idea.


I even like the music...
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