Rotating Power Cylinder Ringbom
- Thread starter fcheslop
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fcheslop
Well-Known Member
Hi Jim, its all magic n mirrors :}
The engine uses the Ringbom principal but due to the rotating cylinder becomes a marginal thing at best. The passage way for the hot air is a bit long and convoluted and the pivot is an air leak point. It was nearly a runner for ages just no cigar until I contacted Huib Visser who had made one . The displacer shaft and bearing and the rotating power cylinders shaft and bearing had to be made from hardened steel and a lapped fit. Standard reamers give too much clearance soo a tool makers reamer was made 0.0003 undersize and the parts lapped with tooth paste all I had.
My shop is basic but with patience it was possible
A link for Ringbom basics
http://www.stirlingsouth.com/richard/thump21.html
The engine uses the Ringbom principal but due to the rotating cylinder becomes a marginal thing at best. The passage way for the hot air is a bit long and convoluted and the pivot is an air leak point. It was nearly a runner for ages just no cigar until I contacted Huib Visser who had made one . The displacer shaft and bearing and the rotating power cylinders shaft and bearing had to be made from hardened steel and a lapped fit. Standard reamers give too much clearance soo a tool makers reamer was made 0.0003 undersize and the parts lapped with tooth paste all I had.
My shop is basic but with patience it was possible
A link for Ringbom basics
http://www.stirlingsouth.com/richard/thump21.html
Mr Heslop - Sir! I am impressed!
What a lovely mechanism to watch! You are certainly demostrating high precision and low friction with your model making. A couple of idle thoughts: (but being "idle" they may have missed the obvious.)....
K2
What a lovely mechanism to watch! You are certainly demostrating high precision and low friction with your model making. A couple of idle thoughts: (but being "idle" they may have missed the obvious.)....
- I wonder if a lip seal on the shaft would have simply had too much friction - and alternative to your High precision boring and lapping process? As lip seals provide a knife edge for sealing - and are lubicated with oil - the friction is very low. The pressure on lip seals is low but increases with pressure on one side - so should retain -1 bar gauge (vacuum) in one phase while allowing higher pressures in the other phase - leak free. But is one side of the piston at atmospheric pressure? I don't understand enough, but if the average pressure rises above atmospheric, does it work better? - or not at all?
- Could you make the shaft smaller to reduce friction - and leakage? - As the air pumps through the centre of the shaft, of course you don't want to restrict gas flow, but maybe there is some scope?
- If the support post were made from something other that a large section of shiny aluminium, would heat losses (hence pressure loss?) be reduced between the displacer cylinder and the working cylinder? Maybe made from a Tufnol product? - Or a shiny aluminium tube (if that's how you want it to look) with minimal material bearing housings and pipework (insulated?) connecting the displacer cylinder and the bearing? - I think the efficiency should go up with reducing the heat lost "in passage" between the displacer and power cylinders. Please can you advise, as I'm not an expert with Stirling's cycle?
- I bought a "Chinese" model Stirling engine, and managed to melt the glass displacer tube... but never managed to get it to run. I guessed that the piston seal - just wasn't a seal. I assume that is critical? But the displacer is just wire wool. Does MORE wire wool, more densely wound, make a better displacer? Does a larger flywheel help?
K2
fcheslop
Well-Known Member
Hi K2, hmm how to answer
Agreed a lip seal may be a better alternative but does the friction not increase as the pressure increases. Also Im a tight wads and like to make everything I can
The air passage way is lined to reduce heat loss . I had some machinable ceramic in my swag stash from the days when I had to do that dirty four lettered word.
The Sirling engines from the land of who flung dung seem to have improved as the early one had power pistons that fitted like an arse in on a pot . I have rebuilt a few over the years
The piston on this engine is graphite so very little friction but more importantly no or little expansion an often missed point on these engines. The cylinder has a stainless liner fitted that may not be obvious in the pics and again very little expansion when heated.
Ive not used wire wool as a displacer but would think it would give a bit of regeneration so would think less would be better but have no practical experience. The only time Ive used wire wool was in my Thermo acoustic engine built to Jan Ridders drawings and it works better lightly packed.
Friction and air leaks just kill these engines and as you found putting extra heat just makes for more grief as I found out myself
The original builder of this rotating style engine just shows a pick as a teaser in one of his books . Recently found out he is a precision tool maker with a fully equipped shop hmmm
The world of hot air engines is pretty friendly in general and most will swap ideas or give pointers when needed although for me language is oft a problem as it seems to be of more interest in the Netherlands and Germany than in the UK
I like a wee challenge although often doubt my sanity building these wee engines .All good fun though
Should you need another test tube I may have one in my stash just shout up.Once the lock down is eased I could chuck one over youre wall or leave it at the Sundrland0
Cheers
Frazer
Agreed a lip seal may be a better alternative but does the friction not increase as the pressure increases. Also Im a tight wads and like to make everything I can
The air passage way is lined to reduce heat loss . I had some machinable ceramic in my swag stash from the days when I had to do that dirty four lettered word.
The Sirling engines from the land of who flung dung seem to have improved as the early one had power pistons that fitted like an arse in on a pot . I have rebuilt a few over the years
The piston on this engine is graphite so very little friction but more importantly no or little expansion an often missed point on these engines. The cylinder has a stainless liner fitted that may not be obvious in the pics and again very little expansion when heated.
Ive not used wire wool as a displacer but would think it would give a bit of regeneration so would think less would be better but have no practical experience. The only time Ive used wire wool was in my Thermo acoustic engine built to Jan Ridders drawings and it works better lightly packed.
Friction and air leaks just kill these engines and as you found putting extra heat just makes for more grief as I found out myself
The original builder of this rotating style engine just shows a pick as a teaser in one of his books . Recently found out he is a precision tool maker with a fully equipped shop hmmm
The world of hot air engines is pretty friendly in general and most will swap ideas or give pointers when needed although for me language is oft a problem as it seems to be of more interest in the Netherlands and Germany than in the UK
I like a wee challenge although often doubt my sanity building these wee engines .All good fun though
Should you need another test tube I may have one in my stash just shout up.Once the lock down is eased I could chuck one over youre wall or leave it at the Sundrland0
Cheers
Frazer
fcheslop
Well-Known Member
Should have also said. An increased crankcase pressure will increase engine power as would using a better heat conducting gas. Then it would have to be sealed and again frictional forces would increase.
On a small coffee table toy like this it would all become pie in the sky its just a toy too amuse this locked in nutter
Keep well
On a small coffee table toy like this it would all become pie in the sky its just a toy too amuse this locked in nutter
Keep well
Thanks Frazer. Most interesting. I'll get my engine out and start investigating!
K2
K2
fcheslop
Well-Known Member
Just be careful as they are addictive. My home is full of the bloody things.
cheers
cheers
Rocket Man
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Ringbom engines have a floating displacer piston. Displacer Piston needs a large diameter rod out through the head. The rod that extends our of the head acts like a piston also it lifts the displace piston up when air pressure increases inside the engine. When air pressure inside the engine increases it basically blows the displacer piston UP until it stops at the head. When pressure in the engine drops vacuum sucks the displacer down with the help of gravity. Small piston diameters are harder to make the engine run because pressure changes inside the engine are very small. It is much easier to get a 2" diameter piston engine to run than a 1" piston. Tolerance must be very close as already mentioned. Engine works best if displacer is made of very thin light weight metal, aluminum .030" thick. I have a 2" power piston with .0002" cylinder clearance. It is best to use cylinder & piston that both have the same expansion rate so when engine temperature changes piston diameter changes at the same rate as cylinder bore diameter. I used cast iron cylinder and aluminum pistons they both have different expansion rates my engine does not run well until it warms up to a certain run temperature so all the clearances stay at .0002". I have a 2.000" power piston, 1.750" displacer piston, the displacer rod is 1.000" diameter. My power piston stroke is .625", Displacer piston stroke is 1.000". Displacer piston length is 2.5"long. Clearance between power piston top dead center and displace at bottom of stroke is .020". I put power piston ring grooves .020" wide, .020" deep, spaced .125" apart full length of the piston but NO rings in he grooves. I can not remember what this piston ring groove are called?????? Pressure drops across each ring groove makes the piston act like it has frictionless rings. I removed all the metal from the inside of my 2"x2" power piston to make it very light weight. I have both pistons inside the same cylinder, power piston on bottom, displacer piston on top.
Anyone that can make this tiny engines run has a lot more patents than me.
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fcheslop
Well-Known Member
The next project is small not like the rotating one 
Just to add another lever of fun
Just to add another lever of fun
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The multiple grooves on the piston are referred to as "labyrinth seals": Each change from piston wall clearance to groove and from groove to piston clearance imparts maybe 10% pressure drop... as gases don't like changing direction and blowing around corners. Usually 6 or more grooves make an adequate seal. There are engineering ways to determine the sizes and number of grooves, but that was 40 years ago and I simply can't remember all the details of the calculations. - Probably on the web somewhere... Usually spaced the same as the width, and depth the same, and there is a ratio for piston clearance Cross-sectional area versus grove volume that affects how many grooves you need. I worked with a guy modelling these on the first Apple desk-top computer... in 1984, and did complimentary modelling using the company Main-frame computer.. setting parameters for overnight runs! - And probably less computing power than a modern I-Phone?
K2
fcheslop
Well-Known Member
Martins equation maybe what you are looking for
cheers
cheers
Thanks!
K2
K2
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