Hot air and stirling engines

[Ian S CParticipant @iansc]

Hi Gordon, I as thinking of you the other evening as I was having a look through this thread, wondering how you were getting on. The rusty bit, Over the top of the burner is a stainless steel mesh in an inverted cup shape that keeps most of the flame contained. It has a slightly different burner on it now, but still very similar. That one came off another engine. The blue hose goes up to a can of water for cooling, but after that trial it has’nt been used, and the hot end below the discoloured area stays reasonably cool, Mark knows not to put your finger too high up the hot cap. The burners for my vertical engines is a doe nut shape, with two or three rows of 1.5mm holes round the inside. Partial speed control is got by adjusting the hight of the burner, ie., up slower, less power, down more power and speed. I have not got fine control of the burner, or that could be adjusted by a govener.

Mark I can see Gordons point about winter, more time in the workshop, less time in the garden etc. NOW i’v sort of got this photo thing sorted I’ll drop in a few pics every now and then. Ian S C

[adyParticipant @ady]

Lots of stirling stuff on youtube.

A fascinating subject

 

http://www.youtube.com/watch?v=6DBktwPf3rk&feature=related

http://www.youtube.com/watch?v=cjjkj-UGboM

 

With a geothermal heat transfer pump system some of them look like they could keep going forever.

http://www.youtube.com/watch?v=OXm3ZmL4I0U&feature=related

Edited By ady on 30/08/2010 01:38:02

[Ian S CParticipant @iansc]

Ady, I havent looked at you-tube, but reading on another site’ don’t beleave all you see on you tube’ the writer thought a kot of the stuf was the hings of dreams, and from what I’v seen some of the ideas are to say the least a little odd. From what I see and read the geothermal system is quite practical, but takes up a lot of space, admitably underground.

For someone wanting a plan of a good woking motor– google The Metal Master and Stirling Page, and look at the first engine, its got a note next to it saying it was taken off, but bought back, its got all the drawings and notes, and if your like me you can add a bit of your own design. The motors are designed and built by David Urwick of MaltA. This type of constrution is preferable to a tin can engine for a serious model engineer, I’v built a tin can motor last year, it works but I’m not overly impressed, mind you its got a good piston and cylinder, I made them 3 or 4 yrs back for a Robinson type engine, I might yet revive that program. Ian S C

[adyParticipant @ady]

Those yootube videos do help you to visualise the stirling process though, when considering a solution.

 

The small models seem to indicate that you need a huge displacement piston and a tiny power piston with a very tight throw on the flywheel to achieve good mechanical success, plus the kind of build skills/mechanical accuracy a watchmaker would be impressed with.

 

The further you move from this, the more energy you need to create motion, usually achieved with a burner.

 

It puts me in mind of the race to build the first chronometer, and the wacky route John Harrison took to get there first, or the rocket with it’s more efficient tubed boiler.

 

From what I can see the key appears to lie with maximising the movement of the gas in the displacement chamber with the minimum of effort.

Edited By ady on 30/08/2010 10:44:28

[Ian S CParticipant @iansc]

Ady , I’v got to up date the program for most of the movie clips, and I’m on land line, so things are a little slow (but its free). A large displacer is required fo a low temp engine with a ratio up to about 20:1, where as for a hi temp motor its 1.5:1 more or less a little one way or the other wont hurt. The one in the photo, hot and cold are 1:1 and is known as a Rider type with two power pistons, the hot one has a stainless steel cap on top of the piston to keep the heat away from the piston crown(its called a Heylandt crown), and the linkage although used about 200yrs ago on a steam engine (preserved in England), Was re-invented for hot air use by Andy Ross in the USA, there is an animated veiw of it on Google. And no even with my smallest engine,2.5cc its not near watchmaking.The engine its based on was in Model Engineer, and that one won the Gnat power competionIt can be built as a Gama or Beta type, mines a gama ie 2 cylinders, I thought that with a 5/8″ bore it would be a bit fiddly putting the displacer rod through the piston, so I took the easy way, I run it on a meths burner, and it will drive a generator to run a 3V radio. Ian S C

[adyParticipant @ady]

This was the route I was thinking about, liquid pistons and bellows being somewhat simpler to make and maintain than machined parts, the key being the maximum displacement of air.

 

I don’t think the nuclear power generation industry  needs to start worrying yet though…

 

http://www.youtube.com/watch?v=f_8GNURkVGY

[Ian S CParticipant @iansc]

I have tryed the Fluidyne Stirling engine pump, it did’nt work very well, I think I made it too big, must try again some day. I saw a tin can type engine with water in it, must have another look. It can’t be very high speed or it would suffer from cavitation, ie inertia effect of the water changing direction frequently. Oh by the way the Fluidyne pump was designed by Dr C. West at the AERE, Harwell, there is a book on the subject “LIQUID-PISTON STIRLING ENGINES”, published by Van Nostrand Reinhold Co. of New York, USA.  Ian S C

[Ian S CParticipant @iansc]

ady, I had a look at the youtube site quite impressed with the motor, could you explain the water filled hose, I imagine it to be a manometer indicating the rise and fall of the pressure, or is there more to it? Ian S C

[adyParticipant @ady]

I think that big hose displaces the hot air in the bottom of the can, like a circulation fan pumping it in and out of the lower hot section to replace the work of the mechanical displacement piston.

 

Inefficient, like a 2 stroke engine, but it appears to work.

If I manage to make one work I’ll post it up, pretty bizzy just now though.

[Ian S CParticipant @iansc]

Hi folks from shaky canterbury, I’m OK, but theres a lot of damaged houses around, and after shocks are frequent. I started yesterday converting one of my engines to a steel wool regenerator/ displacer, but I’ll have to wait till next week to get the steel wool, it costs about $NZ20 out here, should be cheaper in town. It will be interesting to compare this with the original mild steel one, thats iwhen and if the shops open again. Home here in Darfield is within half a dozen Kilometers of the epicenter of a quake similar to the one in Haiti earlyer this year. Ian S C

[Ian S CParticipant @iansc]

I’v got the steel wool, heres the motor that I am modifying. There are more pics in an album, ‘fraid there all webcam at the moment. Ian S C

Edited By Ian S C on 19/09/2010 13:04:36

[Ian S CParticipant @iansc]

Experiment completed, it works but with reduced torque, the revs are up but not enough power to drive the tacho without effecting the output.On opening the motor, a lot of bits of steel wool was found on top of the piston, I don’t want to damage the Teflon cup seal so I’ll go back to the old displacer. You’v got to try these things, if the displacer was at the bottom I might have left it and done further work on it.I have an engine with a 2 1/4″ bore that needs a new hot end, when thats done I may try that one as its up the other way.Ian S C

[Mark Smith 3Participant @marksmith3]

What I did on one of my less successful engine that only just ran normally was drill holes around the top and bottom of a normal displacer and packed it with stainless wool. The engine ran just as well (or badly) as with a normal displacer. Your drop in torque was probably due to the increased dead space. The idea obviously works as that was the kind of displacer in the robinson design. Also David Urwick of Malta did some important work in this area.

Mark

[dcostaParticipant @dcosta]

Helo all.

 

I found information about a powerful Stirling engine (500 Wats)  and I thought it will be interesting to some of the members of this thread.

 

http://www.uwemoch.de/

 

 Best regards

Dias Costa 

[Ian S CParticipant @iansc]

Hi Dias, I think the only problem I would have with the ST05G would be brazing the tubes in the hot end, other than that it seems fairly simple. I really must make an engine with a regenerator, although I think I would go for the Ross Yoke type, I copied a diagram of the motor of the web, all the parts are numbered, but I can’t find the list, no matter.

Mark, I may try that very course silvery steel wool, I think you saw the stuff. The idea of the ordenary steel wool unrestrained is I think that it seals against the cylinder wall. I put the old displacer back. The rod through the piston was a bit stiff (has been for quite a while). I’v got a special reamer for that bit, and took a skim out, it had got some oil on the carbon iimprenated teflon bush causing it to swell. The motor now goes better than ever. At the moment I’m making a new displacer, the old one had a clearance of only 1mm, and at certain RPM it vibrates and touches the cylinder, so I’m making it neerer 2mm. I tryed another wee experiment, took the flywheel and pullys off, turned on the heat, gave it a flick, and away it went, it ran rough and noisy, and with little power, but it goes, for normal running it actually needs a little more weight ie., another flywheel on the other end of the crankshaft. Ian S C

[Ian S CParticipant @iansc]

The new displacer is made from the tube from inside a shock absorber, put a mandrel inside it and turned it down to about .007″ from about .060″, got to be careful handeling it, it ‘s quite flexable. I don’t know, but the thinner the metat, the harder I find it to braze the end on. The end is flanged over to form a cup with a 1/8″ lip, and fitted inside the tube. Ian S C

[Mark Smith 3Participant @marksmith3]

I am about to start a new project and have acquired some sg cast iron billets. Does anyone know what properties sg iron has against grey iron or white iron? Does it have the same self lubricating qualities for instance, and would it be suitable for piston rings?

 

Cast iron I have been using to date has been discarded window sash weights which is very brittle and sometimes I discover a void after a lot of turning.

 

Mark

Edited By Mark Smith 3 on 28/11/2010 17:58:09

[John OlsenParticipant @johnolsen79199]

Cast iron from sash weights can be of very variable quality. I suspect that in some cases the foundry kept a few moulds ready for sash weights and if they had metal left over from a pour that is where it went. On the other hand, some of it was OK, my 1971 Triumph 250 single had an exhaust valve guide made from an old sash weight after the original aluminium bronze item failed. (Triumph please note: Aluminium bronze is not a suitable material for an exhast valve guide for an air cooled motor, it goes hot short and falls to bits.)

 

I would not bank on SG having the same self lubricating properties as ordinary cast iron. The carbon content is much the same, but in ordinary iron it is in the form of graphite flakes, and of course graphite is a good lubricant. In SG iron the treatment causes it to form into little balls…I don’t know for sure but I suspect these may not be graphite any more.

 

So the SG is much less brittle, and hence more suitable for stressed items, but not necessarily so good for sliding surfaces, unless the other material involved is suitable. The crankshaft for my compound launch engine is SG iron, but that runs in white metal bearings.

 

regards

John

[Ian S CParticipant @iansc]

SG Iron is exactly whats needed ,Spheroidal Graphite cast iron,the graphite is free ,and forms a lubricant. Mark, I hear you met Jason when you dropped off the iron at my sisters place, I’ll pick it up later in the week.

Window weights, large 2″ dia OK, smaller ones as often as not hard as glass, some times you get lucky. Ian S C

[Ian S CParticipant @iansc]

Got sick of working on the motor that I’m building, so I got the one I finished a couple of weeks ago, its a Ringbom type that sits on an electric hot plate(or a log burner), after running it for 1/2 an hour or so with a fan on it I thought how about giving it a flat out run. I put a flywheel on in place of the fan, then started it, it ran up to about 1000rpm, the it started to free wheel untill it was down to about 600rpm, then it picked up again to a thousand revs, and just kept up this pattern of running (sort of hit and miss), put a load on and it runs at continuous power, most odd.

   Does anyone know the correct ratio of displacer diameter, to shaft diameter for Ringbom engines, I’m afraid mine are done by guess, the three motors of the type that I have built work, but have little torque.  Ian S C

[Gordon WParticipant @gordonw]

Hi all, I have a question for the experts, – made my leather piston at last, 2mm leather for seal on ally piston. I used a spare cylinder for the “mould”, soaked leather in water for 2 days, then formed round the piston and pushed in the bore, this worked very well and I have a nice piston having also been soaked in oil. However it is to tight in the bore ( 74mm) What is the best way to make a running fit? My instinct is to skim down the piston and clamp leather down tight for a few days, or rub down leather, or bore the cyl., or use leather as a hone with polishing compound (brasso) until it’s a good fit, any ideas? PS. the leather curing chemicals can badly corrode steel and iron and prob other stuff. Use plenty of grease to protect.

[Ian S CParticipant @iansc]

Hi Gordon, marks’ the leather expert (he makes shoes), The way I make cup seals. My seals are fixed to the top of he piston by a large flat nut , usually 3/8″ unf (the thread comes through the piston from the gudgen block. First I make a plug smaller by twice the thickness of the leather. Drill and tap same as the piston. place the leather over the hole (smooth side out),put a large washer/ or the nut that will be used in the engine over the leather that you have punched a hole in and cut say about 1/4″ larger  dia than the plug, (next is my method)work the plug with the leather fixed to it into a tube the size of the cylinder, I then put it into a pot of water and bring it to the boil, let it boil for a few miniuts, then turn off and let it cool. Next day pul the plug out until the edge is showing, take a sharp knife and run it round the end of the tube to cut the leather square, pull the completed seal out, and remove it from the plug. Its now ready to use, just sit it on top of the piston and tighten up the large dia flat nut.I suspect you may be trying to put the seal on upside down, ie., between the piston and the cylinder, it sits on the top of the piston like a cup. he leather should be 1-1.5mm thick, and quite flexable. Marks’ got an explanation back about 10 or more pages, rather than cooking it as I do, he uses a hot air gun. No problems so far with corrosion. Don’t use brasso at this stage, the leather will over many hours polish the cylinder on its own, but the cylinder should be fairly good any way.Ian S C

[Gordon WParticipant @gordonw]

Thanks for that Ian, I’ve made mine more or less like that, using a combination of info’ from Mr. Darlington and Mr. Rizzo. I’m using 74mm bore, piston about 20mm long with piston rod in a bearing to keep it straight. I suspect the leather has swollen slightly, will skim a couple or three thou of the piston and see.

[Ian S CParticipant @iansc]

Gordon, the nut or washer on top of the cup seal should not be so large that it presses the leather against the cylinder wall. I would with a piston that size be tempted to hold the seal in place with a ring about 70mm dia OD, ID 60mm, and about imm thick, held on with 3 or 4, 3mm screws, I’m always looking at ways of reducing weight, thinning things down and hopeing to retain enough strength. I tend to make my pistons so that they will work without a seal, the two latest motors have seals. My most reliable engine is the second one that I built in 1994, its based on J.G. Rizzos Dyna but made a bit more robustly, mainly a much heavier crankshaft, and a carbon impregnated teflon bush on the displacer shaft. Ian S C

[Gordon WParticipant @gordonw]

Great minds and all, thats more or less how I’ve done it. Just been in shop, Temp -5 C. Re-measured across seal and its just about right, but there is a “feather edge” on leading edge, maybe didn’t have it far enough into the bore, past the lead in chamfer, am sure all will be well soon. Must look up theDyna, sounds about right for me.

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