Hot air and stirling engines

[Ian S CParticipant @iansc]

Saw my mate about the mill/lathe,he says that he was rather disapointed with a number of features,ie chuck capacity(chucks 80mm dia very small grip on jaws),max with jaws reversed about 80mm,about .5mm max cut.He found the mill is not even much use as a drillpress,some form of holder with drawbar for milling cutters is needed.The milling area is very small.The tail stock has about 25mm movement.As a lathe it’s quite accurate.Another friend has a BV-20(see the photo on the previous thread,Choosing a lthe),this is a simple little lathe with quite good capacity,I’v used it a few times,it’s got 100mm chucks(3&4jaw)and approx 400mm between centers.Neither lathe has back gear,the BV-20 min speed is from memory 120rpm,max could be up to 2000rpm.Don’t want to be a spoil sport,but I still think NO to the combined set up.I’m perhaps a bit spoiled,my lathe is a WEY YII TY 1324 belt head,I can swing over 18″ in the gap,or 7 1/8″ over the cross slide.It has a 1.5hp 1ph motor.My other lathe that I bought in 1962 for £5 is a Super Adept,center hight 1 5/8″ between centers 6″,it does get some use,its really too small to do very much.

[CirclipParticipant @circlip]

So ok., Morrisons might have been 99p and Farmfoods IS £1, but if you fancy a trip over to Donny, you can buy 12 packs for £9.50 Inc. Vat.,  Direct from the manufacturer.

[Mark Smith 3Participant @marksmith3]

Thanks for that Ian, it’s only an idea at this stage. What do you reckon with regard to laminar flow engines? They seem to have huge dead space which is probably why they are weak and difficult to make work. What about flattening the tube to reduce dead space and increase compression; just a thought..

[Ian S CParticipant @iansc]

I take the hint Circlip,hi Mark I’v got a laminar flow engine here,it has a 5/8″ bore and stroke,i’run it with both 1/2″ and3/4″stroke.The hot end is a 6″ stainless tube with 5/8″ bore,there is a 3/16″dia tube 5 1/4″ long from the power piston back leaving a space at the end for heating,this tube has got cheap stainless pot scrubbers wrapped around it.Its got a 2 1/2″dia by 1/2″ wide flywheel,the big end and crankshaft run in ball races.Its my only air cooled motor,using the cooling fins from an old radio transmitting valve,Goes ok but very little power.They can be made with the hot spot just next to the power cylinder,I havn’t tryed that,I did try to go bigger 1″ bore,but couldn’t get it to go,not even a hint,usually even my worst attempts have shown some life.I havn’t altered the size of the internal tube,that may alter things,also the lengthof the hot end.IAN S C

[CirclipParticipant @circlip]

Sorry Ian, your comments on the Stirlings etc were most informative, but I was loosing the will to live when we were going down the three in one and veedub servicing

 

   Am just plucking the courage up to destroy a carefully constructed at great expence HDD to for bits to put in “Ridders” LT Coffee cup design.

 

     Regards  Ian.

[Ian S CParticipant @iansc]

Hi circlip, I’m in the process of building a low temp motor at the moment,it’s a bit bigger than coffee cup,about 7″dia,don’t really know what I’m doing,but I’m doing it any way.Only items to be bought in are 12 nylon screws to hold the top and bottom together,40K to town and I’ll proberbly hitch hike.

[Mark Smith 3Participant @marksmith3]

Hi Circlip I also got your point; we seemed to go off at a tangent, Sorry. I  have just got my first engine working again after a major format change. It would run but started clattering like mad after a few seconds. I  adjusted and adjusted until I thought it was dead; then I discovered that the setting was well short of the magical 90 degrees. Reset and adjust yet again and it was running tonight for an hour and a half until the water in  the cooler boiled and it stopped. I’m happy.

Mark

[CirclipParticipant @circlip]

Cheers guys, just as a follow on, when a mate of mine (Oh yes I do) received an anniversary present of a new lathe, as part of the inducements, a “Gift” of a design and lumps of metal to build a “Chinese” hot air engine came with it. After many e-mails and Skypes the great day arrived and the damn thing wouldn’t work. Suggestions on other fori (cos this one wasn’t living yet) revealed that with a few mods (Drawings) it came into life and seems to be one of the few that the supplier didn’t have returned.

 

   Come on Klank me old cocker, publish and be damned.

 

  Regards  Ian. 

[MikeParticipant @mike89748]

Hi everybody: Very interesting, all this stuff about Stirling engines. Makes me think I would like to have a go! Of course, they don’t have to be tiny or low-powered. I think it was in the early 1980s that I had a pal who worked for Perkins diesel in Peterborough, and he was involved in the design of one big enough to power a truck. As I recall the fuel of choice was hydrogen. Don’t know whether a prototype was ever built, but the project was abandoned, I believe, because of the availability and high cost of suitable materials to stand up to the high temperatures. A lot of cobalt steel was required, I think.

Nowadays this would be the ultimate “green machine!”

In the same era, Perkins built an experimental gas turbine lorry, which was often seen on test around Peterborough. The exhaust was a huge vertical pipe behind the cab, which gave out a massive heat haze and a smell of burnt paraffin. Alas, another project which came to nought – although its acceleration with a full load was most impressive. I once tried to beat it away from the lights in a 2-litre Cortina!

 

[Ian S CParticipant @iansc]

Welcome to or little group.Interesting about the Perkins expiremental engine,the hydrogen would not actually be the fuel,rather it would be the gas inside the engine and compressed to quite high pressure,maybe 2-3000psi,the fuel would be diesel or kerosene(parafin).You mention gas turbine power,in Christchurch here in NZ we have a manufacturer of electric powered buses with a gas turbine a powered auxillary generator(almost silent)I can’t remember the power of the unit but it replaces the diesil powered geny that they started with.the buses are exported in reasonable numbers around he world.They should have a stirling engine,Christchurch is the home of whispertec,oh well dream on.My largest has 2 1/4″ bore and a power stroke of 1 1/4″,and the smallest 5/8″bore and 1/2″ stroke-there are 8 others in between.I havn’t tryed pressurisation yet,I really should,I have got one that I made so that it could be modified to take pressure.Ian(wot another one)there are very few hot air engines(as long as they are roughly correctly designed)that won’t work,I’v often ended up with a painfull arm flicking flywheels,but eventually,and usually quite unexpectedly away they go after which the start with little or no trouble.IAN S.C.

[MikeParticipant @mike89748]

Hi Ian,

Greetings to NZ from Banffshire! That’s very interesting about the hydrogen – you have had me racking my brains to recall conversations of around 30 years ago. Can’t check with my old pal, because when I moved 500 miles north to Scotland 14 years ago we lost touch, and I believe he has now passed away.

However, I now recall he said the engine could be modified to run on pretty well anything available locally that would burn with enough heat, which leads me to believe you are right about the hydrogen being the gas inside the engine rather than the fuel.

I also wonder if, after a further 30 years of development of high-temperature steels and maybe ceramic substances, the design could be worthy of another look. – Mike

 

[Ian S CParticipant @iansc]

There were a number of vehicles developed to varying degrees in the 1950s-60s,Daf in Holland bus and car.GM &Ford in the USA cars.As you say the motors can be designed to burn just about anything,I saw quoted somewhere even Camel dung for stationery engines in places were it is used as a cooking fuel.Oh well of to bed its 4am!

[Ian S CParticipant @iansc]

Hi Mark, got a dozen nylon bolts,had a fair old chase around town to find them,thought Blacks Bolts & Fastners,they used to,but ended up at Sockburn,at Mulford engineering plastics,they only cost 45c ea.The low temp motor is just about ready to go or not,got to get a 5mm tap for the nylon bolts,we have a handy secondhand shop in Darfield that carries that sort of thing(also the odd milling cutter and lathe tool etc).The motor is not sealed yet a light flip on the flywheel and it does about 6 or 8 turns,I suppose thats not to bad.

[Mark Smith 3Participant @marksmith3]

Sounds good. I ran my motor for an hour and a half the other night. It ran steadily at high speed with only a stop for more water and my comfort stop. Nothing broke and nothing clattered. it finally stopped itself when the water in the cooling tower started boiling, I think I need a bigger water jacket and a fan on the radiator cooler which is an oil cooler from an old vw engine.

[Mark Smith 3Participant @marksmith3]

opps

Edited By Mark Smith 3 on 28/08/2009 21:31:00

[Mark Smith 3Participant @marksmith3]

sorry had a problem with site and entered it twice

Edited By Mark Smith 3 on 28/08/2009 21:29:48

[Ian S CParticipant @iansc]

Don’t know the size of the VW oil cooler,proberbly similar size the radiator in a car heater,tried that without much success,so I pulled it apart,and using the flat tubes,made a radiator with two rows of 8 tubes about 6″ long into a top and bottom tank,this system works well,it’ll go all day,sometimes needs a top up.And yes it has got a fan,little one out of a computer,don’t know if it helps but its a bit more work for the motor,I can also run a radio of that motor,or a small power hacksaw.I’v got the low temp motor assembled,it does’t go yet.With the power con rod disconnected and the piston pushed into the cylinder it just about jumps out again-think compression is ok,think its got to much friction on the displacer gland bearing.It should be going,its sitting on top of an oil column heater,and got an ice pack sitting on top!Just stopping writting now and again to give the little beast a flick or two.

[Ian S CParticipant @iansc]

It goes!,just.Sitting on the heater with an ice pack on top it turns at 20rpm,I’m sure it will improve,don’t know when but if it moves thats a good start.IAN S.C ps I got the 5mm tap-$2 hows that!

Edited By Ian S C on 30/08/2009 12:35:59

[Ian S CParticipant @iansc]

Well it did go,but don’t go now,have to investigate,so I’ll have to unseal the displacer,might be able to reduce the friction a bit,I think thats the reason for the amazing speed,with the heating arrangments it should be doing 200rpm instead of 20rpm.IAN S.C

[Mark Smith 3Participant @marksmith3]

I have a similar problem with my engine. I changed to an aluminium piston because the cast iron one was so heavy it caused the whole engine to jump up and down on the bench. Now it only runs for a few seconds. I used a cast iron piston ring which seemed promising but leaks too much, I think the heat took the spring out of it. I am thinking of using an old fashion idea of a leather seal like a bike pump thaty makes up its own losses. I also found some leakage aroung the displacer gland and have changed to a stuffing box similar to a steam engine using teflon tape to pack the space, this has cured that leak. Now tomorrow, back to the piston. The engine runs reliably and fast with the cast iron piston but the balance is a problem.

[Ian S CParticipant @iansc]

Hi Mark,my best pistons are cast iron,I machine away as much metal as I dare(some times a bit more),I think at least with over 1″dia there is little difference between iron and aluminium(thinner skirt on piston),also smaller clearance,cast iron has lower expansion than steel,its also self lubricating,some aluminium does not run too well on steel.Piston rings cause too much friction on hot air engines.The cup washers are ok,I’v used leather and teflon,both with good results,they allow greater clearance between piston and cylinder.The teflon tape is a good move.My engines seem to have a spell when running up to speed,and when slowing to stop,that they jump about a bit,but considering the lack of balancing isn’t too bad.I think its because I use fairly heavy flywheels that tends to damp out most of the vibration.How did you get that much heat at the piston that it effected the piston ring,or is it a plastic ring like the rings on the piston in a shock absorber,or one of those cheap 12v air compressors?IAN S.C

[Mark Smith 3Participant @marksmith3]

No the ring was cast iron but it hadn’t been heat treated and I suspect it has to be a certain kind of cast iron, not from a window sash weight. The leather cup washer works great so does the teflon tape stuffing box on the displacer rod. The engine now has the best compression I have found yet and it makes up its own losses like a pump. It also runs well on a meths burner again – though the power is down as is to be expected. Quite a few of the old engines had leather cup seals and they were reliable  as well as easy to replace. The same can be said of the stuffing box as new tape can be installed easily without a major tear down. Would I be allowed to bring an engine to the home bush open day do you think?

[Ian S CParticipant @iansc]

As far as meths goes,I’m sure that it ain’t as hot as it used to be.might be just my imagination.YES bring your engine with you,I ment to say so earlyer,there should be one or two blokes with vintage machinery,and a few vintage cars,and theres food.We’v got more excitement here on the twelth Sept,the opening of our local airstrip just on the town side of Darfield,its there for the DC3 for tourist flights,there’ll be a few other aircraft,and even a bouncy castle,should be fun.I suppose I could even take one of my motors down,just need to load up my bike trailer and head of down the road.Even some of the others on this site overseas will know of one of the DC3 Trust members-Ritchie McCaw All Black.IAN S.C

[Mark Smith 3Participant @marksmith3]

 

Now that the comression is better ( actually hard to turn it over) the overheating seams have sorted itself out. I ran the engine for an hour and a half straight on Meths and the water did not boil. Even with gas it didn’t boil and the power output was amazing. I can now make it do some work; don’t know what work yet but something will turn up. Only thing now is that the engine starts and runs with hardly any sound until it gets hot then the piston grows in length enough to lose the clearance between it and the displacer gudgeon at which point there is a light banging noise. I’ll put the piston in the lathe today and shorten it a mil or two that should fix it.

If anyone is interested , being an Orthotist who sometimes makes special footwear for deformed feet, I know something about leather. To shape the cup I reduce the top 6mm of the piston the thickness of the leather being used (after drilling and reaming for the displacer rod) and part it off. Then I push the piston and the top cap into a short tube the same internal dia as the cylinder with the displacer rod down the centre to locate the parts. Mark and drill two holes on opposite sides and counter sink and tap for 5/32 thread. Cut a suitable piece of leather with enough extra to form the cup depth required and mount it under the top cap. Push the assembly into the tube and heat it from the top with a hot air gun. The heat will shape the leather permenantly. There is no need to wet the leather as it has usually got enough moisture in it. When cool trim to the top of the piston top cap, oil lightly and there you have it. Oh, and I turn a slight taper on the top cap (narrowest at the top) to allow the air pressure to push the cup against the wall. I hope that’s as clear as mud. I will try to put a pic up. It’s a bit washed out but you get the idea.

Edited By Mark Smith 3 on 05/09/2009 22:07:01

Edited By Mark Smith 3 on 05/09/2009 22:09:33

[Ian S CParticipant @iansc]

I mak my cup seals usually with one hole,and I’v tried soaking in water and on another occasion,oil and pressing it into a hole the size of the cylinder with a piece of steel bar smaller by double the thickness of the leather and with a bolt in the end to centralise things.I read just recently of using the Dremmel tool to feather the edge while the leather is still in the hole,in the past I’v done it with a sharp knife.I’v got a bit of family history with leather,until just before WW2 my grandfather had a leather manufacturing business in Dunedin,during the war he managed a certain large well known company(the one he sold up to),I’v still got some of his tools,and leather!One thing I like to get is an edge that is as thin as I can get,the pressures in the motor are lower than a bike pump (I havn’t actually tested that,but you’d be pushing things to get better than 30psi).Grandpa used to make quite good bike seats,first one I remember was for an ancient bike my sister had about 1960,in those days you could repair things like that rather than throw them away.IAN S.C

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