The new member with first engine

Discussion on Stirling or "hot air" engines (all types)
loccd
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Location: Viet Nam
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The new member with first engine

Post by loccd » Wed Mar 30, 2011 8:29 am

hello everybody, iam just a baby in stirling engine, iam building a first alpha engine but not finish
- All made from aluminium and brass.
- Cool cylinder diameter = 16mm, long 39mm
- Power Piston has 2 rubber O ring -> i feel much friction
- Hot cylinder diameter = 24mm, long 70mm (include brass part)
- Displacer diameter = 22mm, long 40mm
- Flywheel in plan is 75mm (diameter) thick 10mm, brass
- Stroke in plan is 20mm for displace and power piston
Please tell me
- Can it work?
- How is about ratio of piston, displace and cylinders?
- Is there any problem if power piston without O ring (piston and cylinder are aluminium)
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Thanks!

onecycleDan1990
Posts: 22
Joined: Tue Jan 18, 2011 1:43 pm
Location: Massachusetts, United States

Re: The new member with first engine

Post by onecycleDan1990 » Wed Mar 30, 2011 2:53 pm

Welcome aboard Loccd..
your engine overall looks well made, and for the most part well designed.
However your engine as it is will not run. This is because there is too much friction generated by the O rings. I would make a new power piston without rings, make it a running fit, and cut oil control grooves in it. If proper clearances are used sealing will be adequate and friction acceptable. used I might also consider making the new power piston out of brass, as dis-similar metals have lower running friction. This should be a relatively easy job, considering what you have already done. It is a good initial design. Dimensions and size ratios are well within the norm, and with a low friction power piston I am sure it could run well when finished. An engine intended to run on a gas or alcohol burner would likely do well with a somewhat larger power piston, and the gap between the displacer and the bore should be smaller (one fiftieth to one hundredth of an inch is a good place to start), but your engine will run just fine with the current dimensions. Yours is very good work for a beginner; I have seen some very crude engines out there that still managed to rotate under their own power, they used tin cans and pipe for cylinders, bent wire for crankshafts, and party balloons for power pistons.

Remember not to get discouraged by failures. The great Andy Ross spent years before he got an engine to run, but later became one of the greatest amateur engine makers alive. If your engines don't work the first time, don't give up, change something and try again until it does. You should be proud of what you have done, you put your money where your mouth is and actually built something, which I have yet to do, but would like to.

I'd like to see some photos of it running when it's finished
Ps.
nice pictures, and the engine in those photos is a gamma engine (as opposed to an alpha).

Ian S C
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Location: New Zealand

Re: The new member with first engine

Post by Ian S C » Thu Mar 31, 2011 3:46 am

Loccd, the brass displacer cylinder will restrict the amount of heat that can be applied, if this becomes a problem, make a new one out of stainless steel, it will be quite happy running at a dull red heat for years.
Friction is the biggest killer of hot air engines, you might get away with taking the O rings out, and replacing them with plumbers teflon tape. Roll it into a string,then wind it into the grooves, you dont want two aluminium surfaces rubbing together, they actually try to weld them selves together, cast iron is probebly the best metal, you can run a CI piston in a CI cylinder. A steel or CI piston in a brass, or bronze cylinder is quite good, building thes things has taught me a bit about metallurgy, sorting out the best metals for each job.
There should be a ratio of 1.5:1,the displace being the larger. Yours should work,but there is too much space, you have 30mm space and a 20mm stroke, you only should have 1 to2 mm each end max.
The best dimention for the displacer is, length = 3 X diameter. Your diameter is OK but make it accurate because it must not rub on the cylinder.
Sorry I tend to go on a bit, good building. Ian S C

loccd
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Re: The new member with first engine

Post by loccd » Thu Mar 31, 2011 9:32 am

Hi all,
Today i make flywheel from acrylic 10mm thick, rods from acrylic too (just temporary to test). remove 2 Oring and use lubricant (i feel it better). After assemply, i can rotate flywheel easily , just a little friction, but it cannot rotate longer maybe not enough weight. When it is rotating, use finger cover the hole on left of the base , i can feel air is compressing. But when i burn it by alcohol 90, it can not work.
The problem i think is Ian SC said "there is too much space, you have 30mm space and a 20mm stroke, you only should have 1 to2 mm each end max". So i want to ask you that can i change the troke of displacer to over 20mm - 28mm, while stroke of power piston still be 20mm?
or The flywheel not enough weight?
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Ian S C
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Re: The new member with first engine

Post by Ian S C » Sat Apr 02, 2011 3:27 am

Yes you could increase the stroke of the displacer.
I'v been checking the volume of your cylinders. Power cyl = 4.02cc and the displacer 9,48cc, if you could increase the bore of the power cyl untill it is nearer to 6.75cc, it would be nearer to the 1.5:1 ratio that is the normal for this type of engine. If you could make the power cyl 20mm dia it would be near enough,another way would be to lengthen the displacer by 5mm and leave the stroke at 20mm, and lengthen the power stroke to 33mm.
personally I would be using some were between 10 and 15mm for the power stroke on an engine this size, and a proportional stroke for the displacer. I'v got a 2.25" bore motor that uses similar strokes to what you are trying on a motor with a fraction of the size.
Your flywheel might be a bit on the light side, on a motor with this stroke it will need a reasonably large flywheel, metal (not aluminium) about 100mm dia, its got to take the motor over to the next stroke, its easier with a short stroke (the motor will run faster too). Thats enough of me rambling on.
Oh, make sure there are no air leaks other than a minute one around the rod for the displacer. Ian S C

loccd
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Re: The new member with first engine

Post by loccd » Sat Apr 02, 2011 6:16 pm

and diameter of drilling hole from diplacer cylider to power cylinder is 5mm, i it ok?

Ian S C
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Re: The new member with first engine

Post by Ian S C » Sun Apr 03, 2011 3:31 am

5mm OK, thats about the size I use, and were a plug is required in the end I use 1/4", fine in steel, coarse in aluminium. Ian S C
Last edited by Ian S C on Wed Apr 13, 2011 5:31 am, edited 1 time in total.

loccd
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Re: The new member with first engine

Post by loccd » Mon Apr 11, 2011 8:58 am

New brass flywheel , diameter 84mm, thick 10mm, weight 450gr, still not running


power stroke is 14mm, is it need to reduce power stroke?

Aviator168
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Re: The new member with first engine

Post by Aviator168 » Wed Apr 13, 2011 10:13 am

Something does look right. Can you show us all the parts in a single photo?

This is what I got from your photos and video.

1) The transfer of the working gas seems to take place at the very bottom of the hot cylinder.
2) The crank rod of the hot piston goes in straight.
3) When you combine 1) and 2), it seems to be a gamma stirling.

If 1) is correct, your original spec does not make sense
Hot cylinder diameter = 24mm, long 70mm (include brass part)
- Displacer diameter = 22mm, long 40mm
- Flywheel in plan is 75mm (diameter) thick 10mm, brass
- Stroke in plan is 20mm for displace and power piston

loccd
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Joined: Thu Mar 24, 2011 7:20 am
Location: Viet Nam
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Re: The new member with first engine

Post by loccd » Wed Apr 13, 2011 5:17 pm

Aviator168 wrote:Something does look right. Can you show us all the parts in a single photo?

This is what I got from your photos and video.

1) The transfer of the working gas seems to take place at the very bottom of the hot cylinder.
2) The crank rod of the hot piston goes in straight.
3) When you combine 1) and 2), it seems to be a gamma stirling.

If 1) is correct, your original spec does not make sense
Hot cylinder diameter = 24mm, long 70mm (include brass part)
- Displacer diameter = 22mm, long 40mm
- Flywheel in plan is 75mm (diameter) thick 10mm, brass
- Stroke in plan is 20mm for displace and power piston
------------------------

Yes, it is a gamma stirling, i made mistake at the first post , sorry
* This is full spec now:
- Aluminium Hot cylinder diameter = 24mm, lenght = 70mm (include brass part)
- Displacer diameter = 22mm, lenght = 40mm
- Displacer stroke = 20mm
- Aluminium Power cylinder diameter = 16mm
- Power Stroke = 14mm
- Brass flywheel diameter = 84mm, thick = 10mm, weight = 450gr (is it too heavy?)
but not work, so iam considering some problem
1. Flywheel too heavy?
2. Ratio of 2 cylinders
3. Stroke?
4. Friction (when i rotate the flywheel by hand, it can self rotate 4 turns)
5. Air leak (just a little at the rod hole when i use air compressor to test in water)

Aviator168
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Re: The new member with first engine

Post by Aviator168 » Wed Apr 13, 2011 6:39 pm

loccd wrote: - Aluminium Hot cylinder diameter = 24mm, lenght = 70mm (include brass part)
- Displacer diameter = 22mm, lenght = 40mm
- Displacer stroke = 20mm
This spec does not seem right.
I would expect the displacer stroke to be very close to 30mm (70mm - 40mm).

Also. If you would, make the displacer diameter to be 23mm.

Ian S C
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Re: The new member with first engine

Post by Ian S C » Mon Apr 18, 2011 6:39 am

work out the ratio between the cylinders, 1.5 : 1, the revised power stroke is not too bad, you want a short stroke. Why on earth have you mounted the power con rod out the side instead of inline as you made it with the slot in the rod, you are putting a sideways force on the piston. You could also get rid of a lot of weight on that piston rod, you only should have a bit over the diameter in length in contact with the cylinder, FRICTION is what you'v got to get rid of. The brass flywheel should be OK, wish I could afford brass, mine are steel or cast iron, or anything I can get, one of them is the hand wheel from an old sewing machine. Ian S C

loccd
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Re: The new member with first engine

Post by loccd » Thu Apr 28, 2011 7:54 am

When burning and rotate the flywheel, i see piston move a little, i feel the hot volume is quite small. I intend to change the bigger hot cylinder, with bigger diameter about 32-35mm, of course diameter of displacer has to follow, everything not change. Is it ok?

Ian S C
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Re: The new member with first engine

Post by Ian S C » Fri Apr 29, 2011 3:09 am

Work out the volume of the power cylinder ie., area of the diameter X the hight of the open space when the piston is at the bottom of its stroke, then do the same with the displacer, the ratio for a good motor should be1.5: 1, the displacer being the larger, you could go to 2: 1, as you are restricted by the brass hot cap in as much as you can't run at red heat or you'll have a melt down. Get that con rod on the power piston sorted, its putting unneeded friction on the motor. Ian S C

loccd
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Re: The new member with first engine

Post by loccd » Fri May 03, 2019 5:04 am

Comeback after 8 years, convert some to cnc part
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