Hot air and stirling engines

[Ian S CParticipant @iansc]

Been fiddling around with my version of Jan Ridders single cylinder vacuum engine that was in ME a while back,havn’t got it to go yet,have to do a bit of thinking about it.I built one from a sketch plan in an old ME 10 yrs ago,that one took a yr or so to get going,it now runs like clockwork,so this one will possibly be something similar.I suppose vacuum motors are a form of hot air motor.

[Mark Smith 3Participant @marksmith3]

My pressurised engine is taking shape. The crankcase and side plates are complete with pressure guage and crank bearing set with two dynamic seals. Next step is to turn the piston and the displacer. I have installed a car valve  so I can use my compressor to add pressure before I work out how to make the self pressurising pump. Ian how many engines do you make, Steam? Is a flame licker as powerful as a hot air engine or less so?I will post a pic or two of my latest engine and my vertical engine shortly.

Edited By Mark Smith 3 on 05/10/2009 08:22:21

[Ian S CParticipant @iansc]

Flame Licker/Vacuum,that tells most of it,it opperates by the pressure drop as the flame that is drawn into the cylinder cools.Unlike the stirling engine that is a sealed system that is double acting,powered by both expansion and contraction,also it can’t be improved by pressurisation.Steam,I’v built some oscillators,few yrs back the local high school had a night class and built one there 5mm bore.I then made one 3mm bore and another 1/4″bore,these two were put in boats and sailed on the lake at the local recreation ground,the 1/4″ one wasn’t powerfull enough so I made a V twin vertion,but I havn’t tried it yet.I have got a 4 stroke open crank engine slowly(very)evolving.Built my first motor(thought I’d invented something new)a pop pop boat,then after I got it going dad told me he had one when he was a boy,I think I was 10yr old.Here endeth the history of Ians engines to now,IAN S.C

[Mark Smith 3Participant @marksmith3]

Very interesting history, Ian. You have done much more than me I am a tyro at this game but learning all the time. I have always been fascinated with engines of all types but non captured my imagination as the stirling engine with its simplicty of operation and its potential. Here is a photo of the first engine I built out of junk. It develops quite a lot of power on Gas. I found that if I hold the shaft at a certain speed the torque starts to increase steadily until the shaft gets hot under my fingers trying to slow it down; maybe someone can explain that..

This engine has a 2cm stoke and a 2.5cm bore seen here running on meths.

 

The next engine is my new one designed to be pressurised. It  has a 3cm stroke and 3.3cm bore. The crankcase is from a car generator parted off in the lathe. I then mounted it in the four jaw chuck to face off the part to accept the cylinder flange; quite an undertaking. It made the floor rumble a bit. The cylinder is from a large shock absorber and the displacer is part of a bike frame (chrome molly). I now need to fashion the piston and seals which will be what I found successful to date, being leather cup seal in the piston and a teflon tape stuffing box to seal the displacer rod. I found the pressure guage in one of my junk boxes. At first I have installed a tyre valve to pressurise the crankcase from my compressor until I work out how to make a self pressurising pump driven off the opposite side of the piston from the main crank. I think the cup seal will equalise the pressure across the piston.The crank and seals I have modified from a line trimmer engine. I installed two seals in the bearing set to contain the pressure.

This last image is of a sugar bowl that will become the cooling jacket and the flywheel I think should work after some turning and truing; hope this is interesting.

[Mark Smith 3Participant @marksmith3]

Clive, Gordon and john wood where are you and what are you up to?

[Ian S CParticipant @iansc]

Hi mark,twq of my first attempts at making engines were electric solinoid engines,I wrote a bit in ME vol163 no 3859 in 1989.The motor that I think I could pressurise looks similar to your latest,mine has a bore of 1 1/4″ stroke power3/4″ displacer 1 3/16″.I read lately of making cup seals of Rulon (related to teflon but expands less with heat),the artical suggested using .015″ then molded using heat,melting point of electrical solder is the indicator.I,m looking for something in the stainless ware ie sugar bowl,jug,mug,what ever 55mm dia inside,for the hot end of my biggest motor,think your one is to big for me so you’r ok.For a pressure pump,see Brian Thomas’ self pressuriing stirling engine,it has a bore of 1/8″,and the stroke is the same as the displacer,not sure could be 1/2″.

[Clive1958Participant @clive1958]

Hi Mark, i’m still here, i’ve been trying to spend more time in the workshop and will hopefully post some picture of the results, I have been following the thread with interest.

[Ian S CParticipant @iansc]

Hi clive,I’ll be looking out for your pics,I havn’t worked out how yet(too lazy)Good night all,IAN S C

[Mark Smith 3Participant @marksmith3]

I have to rethink the displacer drive. I had planned to use an offset crank as in my previous engines but the space between the crank and the bottom of the piston means too much angle and side thrust on the displacer rod. Going to go for a bell crank with a scotch yoke to drive the displacer. At some time I will have  to find out how to case harden the slot. does anyone know how this is done? Told you I am a tyro. Also the offset crank uses up the space I had planned for the self pressurising pump that I hope to install at some time.

Edited By Mark Smith 3 on 12/10/2009 05:49:38

[Ian S CParticipant @iansc]

Hi Mark,on my first engine,a V type I used a scotch yoke on the displacer so I could shorten the engine about 2″.I made it out of aluminium.I cut the slot 3/8″ wide,and 1 3/16″ long,into that I inserted a bronze bush with a 1/4″ slot 1″ long,it ran on the 1/4″ crank pin beside the con rod for the power piston.I’v got one on a water pump just running on the aluminium,seems ok.Yes you could case harden the slot,I use Kasenit,think I got it at George Henerys nearly 20yrs ago,I think they still have it.I have on a number of occasions heard of it being discontinued,mainly in Model Engineer.I’d just pack the slot with Kasenit powder,heat to red,hold for a few minutes,then quench in water,the remaining Kasenit will pop of leaving a clean gray finish,thats it no tempering required.If you can get some its well worth it,and it lasts as we don’t use much.I think there are special grades of steel for case hardening,but ordenary mild steel works ok.Havn’t used it much with my motors,but for hard pins etc I use needle rollers out of bearings,also some shafts out of computor parts are hard ie in old printers.Theres a thread on case hardening,sugests 90% charcoal 10% baking soda,might be worth a try.

Edited By Ian S C on 12/10/2009 11:38:14

[Mark Smith 3Participant @marksmith3]

Ok Thanks Ian

[Mark Smith 3Participant @marksmith3]

Closed everything up today and added pressure from my compressor. It leaked like a sieve until I coated all gaskets with cement. Now it will hold 120psi (dropping to 80psi) for 30 minutes. at this pressure It is almost impossible to turn over tdc. But for now I will concentrate on just getting it going at atmospheric pressure to work the bugs out. It seems tight in one place  but I can’t find the cause at present. Compression is very good with bounce but I need to add the big flywheel to help it over tdc as I have only been turning it with a flywheel from the line trimmer – too small.

I realise it will be impossible to start under pressure but was keen to see if the rotory seal on the crankshaft would hold pressure and it does, that’s a start at least.

[Ian S CParticipant @iansc]

Mark I would be starting at atmospheric pressure and slowly increasing possibly 5psi at a time,you may not get much above 20psi for effective performance gain,pressures above this seem to require rather sophisticated heating and cooling systems.performance improvement should be quite good,maybe double non pressurised.Some pressurised motors will not run without pressure.I suspect it might need a fairly heavy flywheel to get it going.I think would like to build something with a Ross linkage,just have to find some bits and see what happens.With these motors hot and cold cylinders generate power,the hot piston has a stainless hot cap on top.Just thinking,a bike pump might be all you need,and could be easier to regulate the pressure.

[Mark Smith 3Participant @marksmith3]

I will start the flywheel process today and, as you suggest, just get it going on atmospheric pressure to start with. I  was just keen  to see how much it would hold. There is a tiny leak in the hot cap (which I mig welded) I will get my son who is a very good welder to tig weld it for me as mig welding is hard to seal up on thin steel.

 

I too will look at the ross linkage at some point. Andy ross apparently got very good performance from his alpha  engines probably because of the better 1:1 compression ratio. Have you seen the balanced rocker mechanism he has on an engine he installed in a locomotive http://www.ent.ohiou.edu/~urieli/stirling/andy_climax/climax.html  Beautiful workmanship I am a million miles from that; just happy to make things work at this stage. Oh well back to the garage for me. I am on leave this week so get to spend plenty of time in there (don’t tell her indoors!)

[Ian S CParticipant @iansc]

Eureka,got the low temp motor going again,about 40rpm.Fitted newer,lighter bearings,and removed the cup seal,even with graphite powder workedinto the leather there was too much friction.At the moment the flywheel is the piece of waist I cut from the edge of the disc cut from the larger of the two fry pans that make up top and bottom of the motor.Outside dia 220mm,depth of rim 9mm x 5mm thick,and I used bike spokes for spokes into an aluminium hub.Gee weld bits,thats great,welding an end on a bit of tube-how thin can you go with stainless?I imagine TIG would be the ideal.That motor of Andy’s is superb,’fraid mine are similar to yours.My only welder is an ordinary 140amp stick welder thet I occasionaly use to blob bits of metal on to other bits of metal,sometimes they seem to join together.

[Ian S CParticipant @iansc]

Mark you asked about the power of flame lickers,I ran my one working one tonight with a little water pump,it did’nt pump much water,but kept it running at 60 strokes per min,can’t remember the reduction but I think the motor would be doing 200rpm or so.The way I was running the thing I need at least 3 hands,if I set it up I think it would pump at 100 spm.The pump is 1/2″ bore x 3/4″ stroke,and it was lifting the water about 1m,might try again next wk and use meths instead of gas(think the gas is too hot).IAN S C

[Mark Smith 3Participant @marksmith3]

Sounds like they are similar to stirlings in power output. Good to hear you got your LTD going, it seems quite large for one of these.

I tried to start my new motor but no go. I need to make the ratio of the piston volumn to the displacer volumn bigger, and the displacer was too loose a fit, but I haven’t got a tube around of the correct diameter so have tried to split a light stainless tube from a vacuum cleaner and braze a section in. The trouble is I can’t seem to braze it without burning the flux and leaving a black mess; tried four times. I have a lot to learn about brazing long lengths. I am going to try using my small forge to bring the job to red heat and introduce the flux and the rod at the same time that way the flame from my blow torch won’t interfere with the flux. The torch doesn’t seem hot enough and the flame is too broad. sometimes the rod melts then it won’t – very frustrating. I look at people who build boilers and marvel at their skill, all those joints and not one leak! I’ll let you know how I get on.

We have a tig welder at work that can handle stainless and aluminium but the thicknesses have to be similar so my son tells me. If all else fails with the displacer I might climb down from my horse and get him to braze the joint with oxy acetylene.

[Ian S CParticipant @iansc]

Hi mark sound tho you have lpg for brazing like me,years ago I got a carbon arc torch for the stick welder,but I hav’nt had a great deal of success with that either,used to be able to go just a few doors down the road and borrow a mates oxy welder,but he died last year and I think he took it with him(we reccon he was going someware hot).the only welding/brazing I’v been taught was with gas in the RNZAF back in the mid 60s(did ok in the trade tests,think it was 92%).In that test we made a little fire shovel,the handle along sightly conical shape with a gas welded seam up its full length,think it was about 16 swg,some of the blokes had great fun blowing holes and getting distortion.Reccon with a bit of practice I could do 20 g with gas,but I’v seen that done easy with MIG.Looked at some MIG welders in Smith’s City today(they’v got a sale)but they still look a bit above my price range.IAN S C

[Mark Smith 3Participant @marksmith3]

I have a gas torch but it is not hot enough. I have also got an old fashion kerosene blow torch like plumbers used to use. If I get everything right and prick the jet it can produce an intense heat but with a broad flame. On my fifth attempt to braze the long joint on the displacer I buried it deep in cat litter and packed refractory small pieces around it the brought it up to bright red heat, sprinkled flux and ran the rod along the joint; it worked. But I also pushed pieces of refractory material into the tube to keep the parts together. At my earlier attempts I had noticed the gap get wider as the heat was applied and the rod would not fill that gap. Displacer is now finished and ready to be installed. I had thought about using my forge but it was a bit windy on the weekend. Cat litter makes a good hearth material as it is made of part fired clay like bisque.

You could try Trade Me for a mig. They are not easy to use to start with. I learned on restoring my Kombi and I found that with panel steel short, well spaced tacks and gradually fill in the gaps seems best with the cheaper types. You can, however, weld half inch thick steel with ease but you need to make a couple of passes.

How rude of that chap to drop off and take his gas set with him you just can’t explain insensitivity like that can you?

[Ian S CParticipant @iansc]

The blowlamp I’v got is a petrol one,it blew back on me one day about 20yrs ago,and I drop kicked it out the door,then went and got the lpg kit,the old blowlamp was mums fathers,He was foreman plumber at Brown&Poulsons in Paisly Scotland.Got a friend who has a MIG,he’s using it to rebuild a Jail Bar Ford van,before he got it he asked me what he should get,and I sugested he should get the biggest he could afford and that I really didn’t know that much about MIG,he did just that(big wire reel included)$600 for a machine worth $3500,he uses co2 rather than argon.I must have a go with it,he finds it a dream to use on both pannel steel,and welding up the modifications on the chassis(the vehicle had been hotrodded),Mig would be a good skill for building our little engines,much less messy than stick,although that might improve if I got an electronic mask.

[Ian S CParticipant @iansc]

Started collecting the bits for the next motor,I hope to build one with a ross yoke with a 35mm bore.Found what I think will make a good stainless hot cap,the stainless tube that is the support tube for an LED garden light,32mm dia 97mm long and .3mm wall thickness,I’ll cut up another one to get the metal required for the hot end,and I’ll make the piston from aluminium,I’ll make the cold piston from cast iron if possible,that way I should get fairly near to ballance.I’v got 2 bits of stainless bar to carve out for the displacer cylinder.Now I’v got to work out what I need for a crankcase.I used to have some window weights 1 3/4″dia they had 18 cast on them maybe 18lb,the only ones I have are rough and about 1 1/2″dia and I want to use it to make cylinder liners with 35mm bore and also the power piston,so of hunting.

[Gordon WParticipant @gordonw]

Hi ,‘m still collecting parts for my new “big” model. Fly wheel- 2 brake discs, one with centre cut out, bolted together and to a flange. Some ideas on welding etc.. Stainless steel is easy to silver solder with correct flux, bad conducter of heat so prop. torch OK. MIG on thin stuff not easy, I do “plug welds” on the 2CV. Have just got some MIG brazing wire, use with argon, I’m still practising but looks good for thin stuff and S/St. N.B not for pressure vessels, before somebody shoots me down.

[Mark Smith 3Participant @marksmith3]

Ian, I don’t envy you boring out all that material.

Gordon I like the idea of disc brakes for big flywheels, might look out for a couple.

I went into a second hand book store the other day and found a 1970 “Model Engineer” which isn’t so interesting except that tucked inside was a 1950 Nov. 23rd ME that had a plan for a hot air engine – not the most sophisticated design but quite large and practical; it used part of a truck chassis as the frame!  The article was by R.F.M. Woodforde, if that means anything to anyone. It is a gamma design, fired by town gas and did 250 RPM. (though he thought ity would do twice that if the piston han been “ground and polished”.  “The displacer chamber”,  as he terms it,  was made from 3″ cast iron down pipe, imagine that! This was turned thin with a carbide tool, because as he said the cast iron is “hard and sandy”.

I pointed out to the chap selling the mags that there was another one inside he said that it was a bonus and ddin’t charge me for it.

[Ian S CParticipant @iansc]

Hi mark,wasn’t Smiths by chance,I’v bought quite a few ME,and other books there,including a bound ME vol 1.The rim of one of my flywheels is from the sort of top hat bit on a large disc brake.I was woundering if I flanged the piece to go in the end of the displacer I might use that as an expirement with spot welding by making small overlapping spots,but I think brazing will be the way I go(I havn’t built the spot welder yet)Gordon,I’v made quite a few flywheels by using 3 steel discs,the center one is bored to take a hub,and drilled for lightness or spokes cut.Then the other two are bored to the dia of the inside of the rim,all three then clamped up,and drilled and tapped and counter drilled for the heads of the cap screws,I usually use 6 screws,alternating from left to right,I’v got a supply of 160mm dia x 8mm discs.I’v made one 14″ dia using 10mm plate,I used 12 1/4″ unf cap screws on that one.Oh I forgot I finnish the outside of the rim is done after its all bolted together.Boring out the stainless isn’t too bad,although I would prefer a bit more metal on the dia,bore out,put on to a mandril then turn down the outside.

[Mark Smith 3Participant @marksmith3]

No, not Smiths but the one in Selwyn St; but I might try Smiths as I am still looking for the article by Andy Ross in an ME from the early 1980s. Tried to see how to get back issues on this site but it isn’t very clear how to go about it or I’m thick – mmm maybe that’s it. Going to the VW october Fest in Oamaru this weekend I am going to take my engine to amuse as it sports a couple of VW parts.

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