Hot air and stirling engines

[Peter Fleming 1Participant @peterfleming1]

Excellent ideas, thanks Ian. I could even use a combination of the two techniques, attach to a substrate and also put pressure on with the tailstock. That was probably my biggest concern with the whole thing. Just going through and “mentally machining” each part I got to that lower plate and thought owwwkkkaayyy, how the heck am I going to hold that slippery little sucker!

 

Pete 

[Ian S CParticipant @iansc]

Peter I’m just looking at the drawings for THE COFFEE CUP stirling engine that came in ME,On a PCD of 105mm there are 6 2mm holes in top and bottom ,if these were drilled the pair could be screwed to a piece of MDF and held in the 4 jaw chuck.Does the one you are building have ball races for the crankshaft,or is it the new one with pointed ends on the crankshaft running in carbon blocks?Ian S C

[Mark Smith 3Participant @marksmith3]

Ian, Is your high temp delta working? How hot do you get the hot side and what do you use for the cold side?

[Ian S CParticipant @iansc]

BETA,GAMMA ok DELTA?Do you mean the free piston with the linear alternator?Ian S C

[Mark Smith 3Participant @marksmith3]

I might be wrong here but I assume by Delta we mean the configuration of the low temp deltaT engines.

 

I have made my rev counter today. It is made from bits I found around my shed, namely: sewing machine parts, 95 tooth gear and worm from a VHS recorder, and a base made from a flywheel I had turned but wasn’t happy with.

 

My latest engine, The Devon runs at 820rpm while the engine you see was doing 980rpm. Next  thing is a torque arm to measure the watts or part thereof.
By the by you said you found a bearing in part of a VHS recorder, well there are two more very nice bearings in the head rotor.

Mark

Edited By Mark Smith 3 on 30/12/2009 02:55:07

Edited By Mark Smith 3 on 30/12/2009 02:56:58

[Ian S CParticipant @iansc]

Hi Mark the LTD motor,I sit it on the oil column heater,and put a cold pack thingy out of the fridge,the max speed so far is about 60rpm.yes I knew about the rotor head bearings,they are massive in comparison-6mm bore,these other ones range from 2mm to3mm without sheilds,they have 6 balls and very free running.Since Peter Flemings been on I,v been looking at Jan Ridders Coffee Cup motor,and I see the power piston is 13mm dia,and the displacer is 100mm approx.8:1 ratio.Mine is 25mm and 150mm about 6:1.I did have a 1/2″dia power cylinder thats about 12:1,maybe about 20mm is about the right ratio.Ian S C

[Mark Smith 3Participant @marksmith3]

Ian can you send me an email as the last one I sent you got bounced back address wrong which I don’t understand as I have sent you mail before. 

I have an LTD that I started a couple of years ago but got sidetracked. The frame with the bearing and crank arangement are complete as are the two aluminium plates, machined and drilled. I found the clear plastic cylinder at the supershed, some sort of jug i think. I just need to make a suitable piston and a foam displacer to finish it. I will look into nylon screws as you say.

Mark

[Ian S CParticipant @iansc]

Theres an Emailon the way hope its quicker than two sent 24th dec,they arrived on the 28th.Ian S CI think i described how I made the foam displacer back on page 3 or so,I used a hot wire.My piston is cast iron,the crown is about 2mm thick and the skirt a bit under 1.5mm thick.Nylon screws-Mulford Engineering Plastic Ltd.,18 Sonter Rd ph 0800 808 809.Ian S C

[Ian S CParticipant @iansc]

hey Mark did it get there?Made a boo boo with the Ross Yoke engine,made the crank case too small,got to find 1/4″ more hight,so I’m digging out a bit of the inards,good thing I over did the thickness of things.The scrap metal I used was about 1/2″ thick,and on taking it to below the rust pits it came to 5/16″,so I left it at that.Boy was it hot,31deg c,yesterday the over night temp went down to zero!If you have some hard plastic rod (8 to 10mm dia) a self tapper in each end,Or as I said to Peter,a little bit of wood ie dowell.If you have any of those little knurled nuts that you find embedded in plastic articals,mainly older stuff,todays things are held together with PK screws.Take those and glue them into the ends of the pastic or wood,it may even look neater than the nylon bolts.Ian S C

[Mark Smith 3Participant @marksmith3]

Yes,Ian your email  came through but when I sent you a reply it bounced back, very odd.

I do have some plastic rod as you suggest, might look at resurrecting that LTD when I have cleared my bench of other projects. Still have to sort out the pressurised engine yet but you have side tracked me with Andy Ross’s artlicle and your little wooden model,so I have made the yoke to go in  a new engine maybe for another nephew. I think it might be possible to drive a counter rotating balance from the rocking lever; it would be simple enough to try just need another bearing on the opposite side to the crank,  and a shaft with the weight and drive pin.

This engine will be a Rider and I have most of the bits I need already, just have to buy a length of AL bar 20mmx50mm to house the two cylinders. Is your engine a Rider?

I got a Mitre 10 gift voucher for Christmas and bought a digital caliper; Magic! It reads imperial and metric, measures inside outside and depth. no more fiddling with micrometers.

Thinking of coming out to you for a visit if that’s alright, but I will ring to confirm.

Mark

Edited By Mark Smith 3 on 01/01/2010 18:44:46

[Ian S CParticipant @iansc]

Not sure about the E mail thing.Yes my motor will be a Rider.I think I’v managed to squeeze things up so that the yoke will fit the crankcase,things are going slowly(they usually do round here).I did consider using aluminium for the cold end,with a steel or cast iron liner.I’m going to make them out of steel with a water jacket,i’v got some 2 3/8″ dia steel,I’ll make the cylinders a cotton reel shape and fit a 2″dia tube over them to form the water jacket.The way things are at the moment with the way its comming together it will weigh a ton (well not quite).Ithink the counter shaft on Andy Rosses motor is driven of the crankshaft.The counter shaft is situated on top of the crankcase between the cylinders,I could add it later.I,m on my 3rd set of digital calipers,cracked the screen on the first 150mm set,got new ones,then needed to measure larger diameter stuff so I got a 200mm set.I still use the micrometer quite a bit.Be good to see you,i’ll do my best to be round to get the phone.Ian S C

[Ian S CParticipant @iansc]

Mark i’v sent you E mail with my cell ph number,so you can text me if you can’t get me any other way.Ian S C Assuming that you have a cell phone!

Edited By Ian S C on 02/01/2010 22:47:09

[Murray TrickerParticipant @murraytricker65189]

Re spacers for coffee cup HAE. I am using 1/8 steel internally threaded each end. However I have not yet finished the engine so cant say how or if it will run yet. Lateral thinking gives me plastic spacers as used in the electronics industry. Go to RS Components web site and look at RS 543-743 as an example. There must be others around. I could not use these ones as I have too little space between the outer edge of the displcaer cyclinder and my already cut top and bottom plate.

Murray T

[Ian S CParticipant @iansc]

Murray my reason for suggesting non metalic spacers is thermal isolation.The small cross section of your fittings will be usfull,but every fraction of a degree you can prevent from transfering from hot to cold the better.not saying I’m any expert,my one isn’t going,but these things take time.Components such as plastic spacers aren’t so easy to find here except in stripped down equipment.Ian S C

[Mark Smith 3Participant @marksmith3]

I have completed the Ross yoke mechanism today.  It is tricky to get right but worthwhile. I now know why a balancing system is needed as, without the reciprocating pistons, just its own action causes a lot of vibration. I’m not sure how I will balance it at this stage maybe solve that when I get the rest of the engine finished.  Andy Ross’s solution was a counter rotating balance wheel driven from gears and mounted above the crankcase. I would like to do away with the gears somehow and mount it  in line with the crankshaft.

The great thing about this drive is how variable it  is from choice of the phase angle to unequal strokes if that’s what your design calls for.  One of James Rizzo’s books (can’t recall the title) volume II has an apendix that shows a way to vary the phase angle at will while the engine is running as a form of speed control.

Ian, did you get my text? your email address still won’t work, There is something wrong with it.

[Ian S CParticipant @iansc]

Got your message OK,that’ll be fine.At the moment my yoke weighs 50 gm and I’ll be able to knock a few grams off that.Just come in ,I’v been making the side rod.I think I may end up making a new bell crank out of thinner aluminium,but I’ll carry on as is at the moment.James Rizzos 2nd volume would be very handy,I’v got vol 1.The E mail does work,slingshot sent me my monthly bill,also got a message from my sister in town.Both sent on 24th Dec,both arrived on the 28th.Even a letter posted at the same time would have arrived a day sooner.Ian S C

[Gordon WParticipant @gordonw]

The engine I’m making is loosley based on a description in old mag. Amateur Work. I’m just reading some of the old instructions, I quote “transfer piston made from sheet iron seamed at joints, joints need not be particularly tight, and one or two small holes should be drilled in the side to prevent air pressure when heated” . I asked this question in the past , and am told it’s a no no. Also the old working hot air engines had all sorts of  regenerator ideas, some of which must have been less than air tight . Any comments anyone?

[Ian S CParticipant @iansc]

Been looking at some of the info on the web,from what I see the counter rotating shaft balances out the imbalance between the two pistons,if the pistons are equal only the balance weight on the crankshaft is needed,but this requires the cold piston to be heavier than it need be,in turn requiring heavier balance weight,I can live with the single shaft.I’m not getting too complicated,no regenerator either.Ian S C

[Mark Smith 3Participant @marksmith3]

HI Gordon, I see your point as I made a displacer that was peppered wth holes at each end and filled with poly pads, yet the engine ran. I want to try it on my reliable old engine to see if that still holds good because that engine refused to run with a small crack at the hot end of its displacer. Sealed displacers  raises the question about moving  regenerators that are tolally unsealed. Most of the books I have read on this subject say that if the displacer is made from thin aluminium or very thin steel, a tiny hole may be drilled in the base to allow some pressure inside stopping the walls collapsing.

All very confusing but it shows there are things about these engines that are yet to be discovered. That’s what is so good about this forum, we can all try things out and report our results – even if not very scientifically – to our fellow postees. 

 

See if you can get an Artlcle by David Urwick  (“Stirling Engines”  More research and development).  from ME18 Feb 1977 it makes for interesting reading on the subject of moving regenerators – in other words open displacers – and dead space volumes.

 

Just as an after thought, I wonder if all has something to do with total swept volumes. The magic numbers I’ve seen are 1:1.5 power cylinder to working cylinder ratio. Yet a rider has in most cases a 1:1 swept ratio. It would be interesting to see if a hole in the displacer-like extension to the hot piston made a difference.

Ian, can you post a link to that site you were looking regarding balancing yokes.

Mark

Edited By Mark Smith 3 on 04/01/2010 19:42:34

Edited By Mark Smith 3 on 04/01/2010 19:44:55

[Ian S CParticipant @iansc]

Whole lots of things here.Ratios 1:1.5 normal for a high temp engine,1:20 low temp,and 1:1 for a Rider,with the Rider the hot cap (Or Heylandt crown)is there to keep the heat away from the crown of the piston and if it leaks,that space becomes dead space.With the ordenary engine that we usually see may have the regenerator built into the displacer as in the full size Robinsons,in the old ones lots of different things were tryed,coils of wire strips of iron,wire mesh etc etc.Stainless mesh or shim stock or stainless steel wool is good(AND CHEAP).With an ordenary hollow displacer,no holes inside the chamber,I make mine with a hollow shaft so that it is vented to atmosphere.Its the volume tha counts,the displacer must present a solid bulk.The fixed regenerators are sealed to atmosphere,and the air passes through between the hot and cold side of the engine.Regarding yokes ,I’ll look for it again.Ian S C

[Ian S CParticipant @iansc]

The best way is to just google “ross yoke”,lookon the web and images,then you’ll be like me overcome by the profusion of information.Ian S C

[Gordon WParticipant @gordonw]

I’ve been re-reading my old tech school Moor & Winstanley (?) Heat Engines. Mostly steam & valve gear etc. Published 1958 ! no wonder I know nothing. No ment. of hot air, but does seem to show that all combustion engine power is directly proportional to the compresion ratio. How the comp. ratio of a hot air motor is calculated I ‘m not sure, but the dead space must be relevant.Also seems likely that a leak in displacer will have less effect at higher speeds? Will now re-read book. Apologies about my earlier remarks about Ross yokes and friction, getting confused over ross yoke, scotch yokes, scotch links etc.

[Ian S CParticipant @iansc]

When I went to tech in Dunedin,our 5th form mechanics text book was Brown & Bryant,Engineering Science vol 1,published in 1937,and based on stuff 50yrs before that.We did have a heat engine laboratory,gas and oil engines and a steam engine,no hot air engine,I’d never heard of them until the late 1980s.A lot of the guys ended up at Hillside Workshops working for the NZ Railways building and maintaining locos and rolling stock.There is more taught about hot air engines now,and a majour part of the engineering school at Canterbury Uni,is devoted to hot air engine development.I’v used a Scotch yoke for the displacer on my first engine,a little V type.With a leak you won’t get to higher speeds if it goes at all,I think most of us have leaking displacer problems from time to time,thats the reason for my hollow shaft on the displacer,I can solder the cold end of the displacer,rather than Araldite,although that works OK.The idea ofcompression ratio is a bit different to IC engines.If the power piston is say 30mm dia and has a stroke of 20mm,the displacer of the same dia must have a stroke of 30mm,or it can have the same stroke and a larger bore.Ian S C

[Gordon WParticipant @gordonw]

Hi Iansc, yes but, I think it’s more complex, I/C  real cr varies with valve overlap, cyl. filling etc, not just the mechanical ratio, also turbine cr, and the rotary eng. which can’t be made with a high mech. cr. Apologies for rambling, getting cabin fever, been snowed in since xmas. Moorfield & winstanley, updated 1947, reprinted 1958, can’t believe I passed an exam on that. Trouble is not one bit of it has been any use, except for model making ideas. Having not much else to do I’m trying to re-read it, and might invent the steam engine.

[Ian S CParticipant @iansc]

Yes your Moorfield & Winstanley was of use,it help to form the interest in things mechanical.Mark the low temp motor is going sort of,got to get it properly balanced,its got a bit of solder wrapped around the rim plus some blu-tack,those holes I drilled in the rim were a bit over done,I’ll fill them one at a time until I get a balance,a bit of solder should do the trick!Took some more weight of the Ross yoke,its now about 40gm,down a bit from the 50gm it was when you saw it,starting on the crankshaft tonight.Got to think about the seal for the bearing,got some low friction plastic washers that’ll be a good start.With the temperature just under 25 deg C I think I’ll conclude the test run on the LTD motor-I’v got the heater on under it and two ice packs on top.Just been looking at a leather cup seal and thinking if I take the gudgen out of the cast iron piston,take the cup seal with a washer each side and a nut to tighten it up I might be able to get rid of a bit more friction,oh well something else to try!Ian S C

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