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AlexK
10-09-2011, 05:19 PM
My son and I have build a Grizzly horizontal Stirling engine.
The problem is that it does not want to work with a regular alcohol burner.
It takes a Map gas torch to get the heating cylinder red hot to keep it going.
There is no too much friction. If you flick it with no heat it'll rotate 5-6 times before stopping.
Cooling cylinder and cooling piston have pretty good fit. When oiled there are no visible air leaks between cooling piston and the cylinder.
But heating piston was machined pretty loose inside heating cylinder. There is a gap between cylinder and piston about 1.5mm
The inside surface of heating cylinder is pretty rough too.
Is it OK? I am thinking about machining a new heating cylinder on a lathe.
Part #21 in this manual - http://cdn0.grizzly.com/manuals/h8101_m.pdf

My questions:
What material should I use? Aluminum or steel?
How thick the heating cylinder wall should be? The kit's cylinder has very thin - 1mm walls Should we try to get it as thin as that or a little thinker wall is OK too?

Thanks,
Daniel & Alex

duckman
10-09-2011, 05:42 PM
If you have a gap of 1.5 MM it will never run that's about .060". :D

The Doctor
10-09-2011, 06:03 PM
You need to minimize friction.

The "heating piston" is the displacer, 1.5mm clearance should be OK. Inside surface of heating cylinder not critical.

Ed

ammcoman2
10-09-2011, 06:57 PM
The cooling piston or power piston should be the best fit you can achieve without binding.

The other thing to bear in mind is that these engines have very little power. Therefore all sliding surfaces should be clean and dry especially this cooling cylinder/piston. If oil is to be used on the other parts then the lightest grade instrument oil (Starrett?) you can find should be applied sparingly.

You could try putting an insulating gasket between the flange # 21 and the body to minimise transfer of heat. You could try cooling the heating cylinder (displacer) fins as a test. On the one I made (Jerry Howell's Vicky Victoria) this gasket is 1/4" thick tufnol (I can't remember for sure about the material though - it's been a while).

Finally verify that there are no air leaks anywhere in the sytem. It should be a closed loop system.

All the best.

Geoff

gary350
10-09-2011, 07:22 PM
I have built several sterling engines.

Small engines have small power so it doesn't take much friction to keep the engine from running.

The sterling engine is a closed system. Air expands and pushes the power piston in the first 1/2 cycle. Air contracts and sucks the power piston back in the second 1/2 cycle. If you have ANY oil inside the closed system its smokes and expands all the time so the second 1/2 cycle can never suck the power piston back. Clean the whole engine with carburetor cleaner. Use graphite for a lube. Moving surfaces need to smooth as possible.

If the piston is made of a different metal than the cylinder wall they can expand at a different rates when heated. When the engine gets hot if the clearances get larger the engine looses power because it is leaking gasses past the piston. If the clearances get tighter then you have more friction. Use your machinist hand book to look up the expansion rate of different metals and try to use metals that expand at about the same rate. Put .010" piston ring grooves in all your pistons 1/8" apart. Grooves are .010" wide and .010" deep but there are NO RINGS. These grooves act like piston rings because they cause pressure drops at several places along the piston. Grooves can be half round shapes. I wish I could remember the technical name for these grooves I could look it up and give you a link so you can read about them.

In places where you can use oil be sure to use extremely thin oil. Thick oil will over power the tiny engine.

A little engines can be very tricky to get it to run. I see your engine has a beam with 2 rods. I would make the beam and rods as light weight as possible. Make it out of aluminum to reduce weight and mass. Drill the beam full of holes or mill it in the shape of an I beam to reduce weight. Reduce the weight of the piston too.

Some extremely small engines have a counter weight on the flywheel to lift the piston. The counter weight is on its way down when the piston is on its way up. The counter weight has to make the weight of the piston equal zero weight. Probably all you need is to make the rod on the side away from the piston heaver so it counters the weight of the piston. You can drill holes in the beam on the piston side to reduce weight on that side. Unhook the rod from the crankshaft and work on it until it balances.

I love a good challange some of these engines can really strain your brain but its all common sense and basic science.

Here is a link to 4 of my sterling engines with videos, sound and photos.

http://www.ebay.com/itm/180735651609?ssPageName=STRK:MESOX:IT&_trksid=p3984.m1559.l2649

SGW
10-09-2011, 07:53 PM
I've built exactly one Stirling engine (Jerry Howell's "Miser") so what I say about this may be total rot, but I'll give my thoughts. Believe them at your peril. :D

The two big enemies of a Stirling engine are friction and air leaks.

Stirling engines require "little or no friction" to be an order of magnitude less than any other "little or no friction" situation you may be familiar with. As an experiment, I suggest you remove all the oil. Don't oil anything. Even the lightest oil can cause way too much drag. You say you are oiling the power piston and cylinder. That may be the problem. Use powdered graphite as a lubricant and don't overdo that, either. Ideally, when the cylinder is held vertically the piston will slide through easily under its own weight, but if you close off the bottom of the cylinder the piston will sit on the column of air and not leak. That is hard to do.... Did you lap the cylinder bore so it is smooth, round, and to-size? The piston/cylinder need to fit each other well enough so nothing else (e.g. oil) is needed to get an airtight seal.

Is the engine balanced? That is, with both ends of both cylinders open to the atmosphere so nothing gets pressurized, when you spin the engine by hand does the flywheel stop randomly, or is there a particular stopping point it seems to favor? It should stop randomly. I see nothing in the instructions that mentions this, and it matters.


My take on it, anyway....

bob ward
10-09-2011, 08:28 PM
If you've not been there, there are vast amounts of info on Stirlings and indeed many model engines here.

http://www.homemodelenginemachinist.com

Bob Fisher
10-09-2011, 09:17 PM
I've also built the "miser".My engine would not run at first, tracked it down to the crank pin which was not EXACTLY square to the flywheel. the power piston is graphite and the cylinder is cast iron. A good fit is critical and NO oil is needed and should be avoided. Mine runs fine on the heat from a night light bulb, really gets cranking with a little more heat. Bob.

AlexK
10-09-2011, 11:04 PM
Bob, where did you get graphite for the piston?

AlexK
10-10-2011, 02:17 AM
Geoff,

where can I find these "insulating gaskets" or material for it?

Thanks,
Alex


The cooling piston or power piston should be the best fit you can achieve without binding.

The other thing to bear in mind is that these engines have very little power. Therefore all sliding surfaces should be clean and dry especially this cooling cylinder/piston. If oil is to be used on the other parts then the lightest grade instrument oil (Starrett?) you can find should be applied sparingly.

You could try putting an insulating gasket between the flange # 21 and the body to minimise transfer of heat. You could try cooling the heating cylinder (displacer) fins as a test. On the one I made (Jerry Howell's Vicky Victoria) this gasket is 1/4" thick tufnol (I can't remember for sure about the material though - it's been a while).

Finally verify that there are no air leaks anywhere in the sytem. It should be a closed loop system.

All the best.

Geoff

SGW
10-10-2011, 07:06 AM
You can probably find any kind of gasket material you want at www.mcmaster.com

ammcoman2
10-10-2011, 09:26 AM
When I bought the original plans and a kits of "hard to find" parts from Jerry at NAMES, the gasket was made from a brittle white material. Of course I broke it while machining to size and had to find a replacement.

I had built a router base plate from clear Lexan a year or so prior to this project so I made the insulator from the original black router base. I think it is that phenolic impregnated cloth material but I can't remember the name. It comes in brown as well. Perhaps someone could remember what it is called.

Geoff

ammcoman2
10-10-2011, 09:29 AM
Jerry Howell's site http://www.model-engine-plans.com/ has graphite rod in two different diameters. The cost is reasonable.

Geoff

Bob Fisher
10-10-2011, 09:51 AM
Just a note on machining graphite, it is messy!Be careful not to track the dust through the house. Don't ask me how I know this.Bob.

gary350
10-10-2011, 11:09 AM
Geoff,

where can I find these "insulating gaskets" or material for it?

Thanks,
Alex

Aluminum and copper roof flashing both make excellent high temperature gaskets. If you don't have gaskets on you engine then that may be part of your problem. You can buy this at Lowe's, Home Depot, and any lumber yard it comes in many different size rolls. The aluminum is easy to cut and it is working great for me.

If you need a harder thinner gasket aluminum soft drink cans work fine.

EVguru
10-10-2011, 12:05 PM
where can I find these "insulating gaskets" or material for it?


Aluminum and copper roof flashing both make excellent high temperature gaskets. If you don't have gaskets on you engine then that may be part of your problem. You can buy this at Lowe's, Home Depot, and any lumber yard it comes in many different size rolls. The aluminum is easy to cut and it is working great for me.

If you need a harder thinner gasket aluminum soft drink cans work fine.
Aluminium and copper hardly count as insulators though!

Traditionally Asbestos sheet was the material of choice (I have an old 1960's Model Engineer article on building a similar engine). Today the best performing material would probably be a machinable ceramic like Macor. It's expensive, but sometimes turns up surplus very cheaply.

ironnut
10-10-2011, 12:08 PM
As stated by previous posters, Stirling engines have a very modest power output. Friction is the enemy, and poor fits and alignment will cause a lot of grief. Stirling engines depend upon the heating and then cooling of the confined air (working gas) inside of the engine. The displacer shuttles the air between the hot and cool sections of the engine, alternately heating and cooling the air. Hot air expands pushing the power piston out of its bore and cooling pulls it back in.

I built this one for my dad a number of years ago. It will run for about 20 minutes while sitting on a cup of hot water. It will run a bit faster if you put an ice cube on the top surface. The chamber is about 5 inches in diameter separated by a ring of polycarbonate sealed with O-rings. The top and bottom plates of the chamber are 1/8" aluminum. The displacer is a disk of rigid foam insulation. The power piston is 3/8" diameter CRS running in a bronze cylinder, oil lubricated. The flywheel is a ring cut from a piece of water pipe and the spokes bronze welding rod. If you look closely on the second picture you can see a small piece of lead glued to the inside rim of the flywheel to balance the rotating parts (2 o'clock position). The main spindle bearing was a actuator bearing from a 3" hard drive and the crank bearings for the displacer and power piston, miniature ball bearings from an old computer tape drive.

The design is loosely based on an article in an old issue of Home Shop machinist. I was surprised that it still ran quite nicely after it had been sitting in my dad's house for several years. I think I used 3-in-one oil to lubricate the piston and the guide for the displacer rod.

gordon

http://i1121.photobucket.com/albums/l515/FEnut/IM001385Small.jpg

http://i1121.photobucket.com/albums/l515/FEnut/IM001365Small.jpg

Bob Fisher
10-10-2011, 07:24 PM
Nice looking engine Iron, looks like a Miser but more simple to build. Part of the fun of building the "miser" was the tapered fluted support column and the fluted power cylinder.The flywheel, with 5 tapered spokes, also fluted along the rim add visual impact. Just an exercise in machining skills .I am now recalling buying the plans and the hard to find bits from Jerry Howell at the NAMES show about 15 yrs. Probably the most fun building than any other engine for me. Bob.

AlexK
10-13-2011, 02:28 PM
We filed off probably 30% off the connecting rods, hinges etc.
Degreased the piston/cylinder and lightly lubricated it with graphite.

It would barely run with my map torch on full and heating cylinder red hot. But when I add a little bit of turbine oil onto the wall of cylinder it runs runs pretty well. I guess it means I have air leak that is getting sealed by oil.

SGW
10-13-2011, 04:54 PM
Yeah, that piston/cylinder fit is extremely critical. Ideally, lap the bore parallel and round, then machine and lap the piston to fit.

Could you change to a graphite piston, if it isn't one already? It's self-lubricating and can be brought to final size by holding a piece of flat paper bag against it while it is rotating in the lathe.

gary350
10-13-2011, 06:11 PM
As stated by previous posters, Stirling engines have a very modest power output. Friction is the enemy, and poor fits and alignment will cause a lot of grief. Stirling engines depend upon the heating and then cooling of the confined air (working gas) inside of the engine. The displacer shuttles the air between the hot and cool sections of the engine, alternately heating and cooling the air. Hot air expands pushing the power piston out of its bore and cooling pulls it back in.

I built this one for my dad a number of years ago. It will run for about 20 minutes while sitting on a cup of hot water. It will run a bit faster if you put an ice cube on the top surface. The chamber is about 5 inches in diameter separated by a ring of polycarbonate sealed with O-rings. The top and bottom plates of the chamber are 1/8" aluminum. The displacer is a disk of rigid foam insulation. The power piston is 3/8" diameter CRS running in a bronze cylinder, oil lubricated. The flywheel is a ring cut from a piece of water pipe and the spokes bronze welding rod. If you look closely on the second picture you can see a small piece of lead glued to the inside rim of the flywheel to balance the rotating parts (2 o'clock position). The main spindle bearing was a actuator bearing from a 3" hard drive and the crank bearings for the displacer and power piston, miniature ball bearings from an old computer tape drive.

The design is loosely based on an article in an old issue of Home Shop machinist. I was surprised that it still ran quite nicely after it had been sitting in my dad's house for several years. I think I used 3-in-one oil to lubricate the piston and the guide for the displacer rod.

gordon

http://i1121.photobucket.com/albums/l515/FEnut/IM001385Small.jpg

http://i1121.photobucket.com/albums/l515/FEnut/IM001365Small.jpg

I have been wanting to build one of those low temperture stirling engines. It is interesting if you set it on a hot cup of coffee the engine runs in one direction. If you set to on a cold soft drink can then the engines runs in the opposite direction. Where did you get your plans? I have a photo in a book that shows a low temperature stirling engine with a counter weight for each piston.