By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Forum House Ad Zone

Hot air and stirling engines

All Topics | Latest Posts

Search for:  in Thread Title in  
<< First < Prev 1 2 3 4 5 6 7 8 9 Next > Last >>
Ian S C26/08/2009 16:55:45
avatar
7468 forum posts
230 photos
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 C28/08/2009 12:16:30
avatar
7468 forum posts
230 photos
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 328/08/2009 21:26:11
avatar
175 forum posts
36 photos
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 328/08/2009 21:26:47
avatar
175 forum posts
36 photos
opps

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

Mark Smith 328/08/2009 21:27:45
avatar
175 forum posts
36 photos
sorry had a problem with site and entered it twice

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

Ian S C29/08/2009 14:03:36
avatar
7468 forum posts
230 photos
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 C30/08/2009 12:31:49
avatar
7468 forum posts
230 photos
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 C02/09/2009 13:04:35
avatar
7468 forum posts
230 photos
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 303/09/2009 09:01:07
avatar
175 forum posts
36 photos
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 C03/09/2009 11:50:48
avatar
7468 forum posts
230 photos
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 304/09/2009 00:04:49
avatar
175 forum posts
36 photos
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 C04/09/2009 11:44:00
avatar
7468 forum posts
230 photos
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 305/09/2009 21:59:25
avatar
175 forum posts
36 photos
 

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 C06/09/2009 12:58:50
avatar
7468 forum posts
230 photos
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
Ian S C06/09/2009 13:55:31
avatar
7468 forum posts
230 photos
I,v been looking at the other of our photos and I see a bit I missed at first,the holes in the piston,two tapped yes I saw those,but I missed the other two,I'v just been letting the air come up the gap if any between the piston and the cylinder,but I think you have an answer to that.
Mark Smith 307/09/2009 10:01:50
avatar
175 forum posts
36 photos
No Ian, The other two holes are a mistake. I broke a tap in the hole, not enough oil, and had to turn the cap 90 degrees and redrill and tap. That's why the extra holes, But you may have hit on something to push the lip against the wall. I used a taper on the top cap to allow the pressure to get at the cup and force it against the wall. The compression in an unpressurised engine is impressive. I don't know how teflon is made but if it could be shaped like leather that would be even better.  I am so impressed with the results I will use the system I described above on future engines until someone shows me something better. In his book, Making Model Stirling Engines Volume 2 James Rizzo also describes a leather sealed piston for the Lehmann engine. 
I think that I will make the piston like a bobbin to make it lighter on Beta type engines. This allows the displacer rod to pass up the centre, a flat on one side to locate the main con rod and reduce friction from the whole piston wall.
Ian S C07/09/2009 12:21:43
avatar
7468 forum posts
230 photos
Oh well nice try,thought I was on to something there,I might try it any way.I'v tried a little valve in the crown of the piston,I think a reed valve would have been better in that case,didn't notice any improvement,so I took it out.I'v got one motor with a piston in the form of a bobbin with the recessed area filled with a ring of teflon,it runs on plain as supplied brass tube 5/8" bore.I find teflon is a bit stiff for my idea of a cup seal,it can work though.Can't remember but I think I turned the teflon cup seal out of solid.IAN S.C
Ian S C13/09/2009 12:55:34
avatar
7468 forum posts
230 photos
I think I'v found the problem with the low temp motor,it appears that very fine particles are coming of the foam displacer,so I'll have to find some of higher density.I'm sure that these particles adhere to the cylider and piston.Took two of my motors down to the opening of the new airstrip on Saturday but didn't run them(would have if someone interested),great day ,lots of people,lots of flying.If after changing the displacer the LTD motor doesn't work,I'll take a thou of the piston and fit a cup seal.
Mark Smith 316/09/2009 10:54:41
avatar
175 forum posts
36 photos
I changed a bearing in the connecting rod at the piston end and now the engine won't go. It has good compression no tight spots and timing is right bu it just refuses to run after several hours of reliable activity. Something is wrong but at this stage i don't know what that is. Oh well, tomorrow...
Ian S C16/09/2009 12:15:28
avatar
7468 forum posts
230 photos
Hi Mark,you'v just got to look a the thing the wrong way and they go on strike.Did you shorten the piston?Is the new bearing square.No leaks in the displacer.I might have a cure for my motor,in my paint supply I found some silver paint that is ok on foam(I think its for making christmas decorations),I'll see if that seals the fluffy surface on the displacer,then I'll have another try,it only went once,and I'm not sure what happened,but the other day I had it outside and took he piston out,turned it upside down and turned the flywheel and noticed very small particals get blown out of the power cylinder(they glistened in the sunlight).
<< First < Prev 1 2 3 4 5 6 7 8 9 Next > Last >>

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Sign up to our Newsletter

Sign up to our newsletter and get a free digital issue.

You can unsubscribe at anytime. View our privacy policy at www.mortons.co.uk/privacy

Latest Forum Posts
Support Our Partners
cowells
Sarik
MERIDIENNE EXHIBITIONS LTD
Shopping Partners
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest

 

Donate

donate