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Hot air and stirling engines
| Ian S C | 26/11/2009 01:01:08 |
 7468 forum posts 230 photos | The stuff is here,I'll get some of it to you.Spent the last day or so sorting the bandsaw out so that I can cut metal for this motor,now that I'v got Andy Ross's artical I can get a few meassurements without using hit and miss,with more miss than hit,Mine will be a little simpler,the one in the ME has a regenerator and a balance shaft.IAN S C |
| Mark Smith 3 | 26/11/2009 04:34:02 |
 175 forum posts 36 photos | Thanks, Ian, look forward to it.
Mark |
| Mark Smith 3 | 30/11/2009 18:12:38 |
175 forum posts 36 photos | Think I have found the reason my pressurised engine goes for a short time or very pooly it's to do with the ratio of 1 to 1.5 swept volumes. Mine is nearer 1 to .75. Also tried the hollow displacer filled with stainless poly pads. It made no difference, the performance wasjust as good or bad depending how you look at it. I might use one of my reliable engines for further experiments along the lines of moving regenerators.
Mark |
| Ian S C | 01/12/2009 11:00:07 |
7468 forum posts 230 photos | Mark can you bore the power cylinder out a little and put in a bigger piston,how thick is the cylinder wall,its either that or change the crankshaft,which might be the better way.I tried a moving regenerator a few years ago with similar results,I used stainless polly pads which are much finer than the ones I saw at your place,I used the coarse ones in the laminar flow engine,I think I may have used steel wool as used by painters.What pressures have you tried,proberbly run into difficulties if you get too much ie much over 20psi.IAN S C |
| Mark Smith 3 | 01/12/2009 18:08:26 |
175 forum posts 36 photos | Pretty sure I can correct it with a shorter conrod to the piston and a different (ScotchYoke) to drive the displacer. The reason why the ratio got out of hand was the lack of space in the crankcase for the off set crank which led to a longer con rod to stop the piston coming too close to the the displacer mechanism. I haven't tried to run it with pressure yet I want to get it going reliably at atmospheric first. I think the moving displacer will work once everything else is right.
Mark |
| Ian S C | 02/12/2009 11:36:37 |
7468 forum posts 230 photos | Ah you'v got the right ratio at the crank,just got some dead space between piston and displacer.If you are running at atmospheric pressure you need to have a vent to atmosphere in the crankcase,I found that with one of mine that I was thinking of pressurising but until now I haven't tried it.With the crankcase closed it ran for about 10 seconds,must have a go one day.IAN S C |
| Mark Smith 3 | 08/12/2009 10:24:14 |
175 forum posts 36 photos | Thanks for the Andy Ross and David Urwick articles, Ian, you are a champion. The rider engine seems to be the way to go for more power per cc. Interesting, too, how phase angle is determined on the Ross yoke by the distance of the upright of the T from the crank pin.
Also of interest is the different assertions by both writers about dead space. Ross asserts that dead space in the cold section is detrimental to performance but Urwick says that he tried different lengths of tube up to 6 feet between the power cylinder and the working cylinder with little difference in performance. This last view is supported by Read in his book Stirling Engines where experiment showed that dead space was less a problem in the cold end than the hot end. Urwick seems to be saying, as I asserted, that the air in the lower third of the engine is merely a vehicle to transfer the pulse of pressure to the piston and plays no part in the transfer of heat to and from the fluid.
How about a thought experiment: imagine a long room with all windows closed and a door at the north end and a door at the south end. The door at the south end is slightly ajar and the door at the north end is closed. Someone opens the north door and without delay the south door shuts from the instant pressure changes in the room. I have seen this happen - might explain a few ghost stories, what think ye? This sounds a bit like the mystery of: "If a log falls in the forest and there are no ears nearby does it make a noise?".
Anyway, enough rambling. I have been conned by my Grandson's cousin to make him an engine too; and that is occupying my time at the moment, my own engines are on hold for the time being. My grand son's engine now has a small generator to power a transistor radio, and a safer meths burner with fire box along the lines of yours but with a fibre glass wick.
Mark
|
| Ian S C | 08/12/2009 11:35:54 |
7468 forum posts 230 photos | I think the main thing to worry about on say a twin cylinder set up is keeping the air velocity down in the transfer tube,rather than trying to reduce dead space by reducing the size of the tube.The air at the hot end doesn't go anywhere,it just nudges the next bit of air down the line and so on,there is proberbly a bit of circulationbut I don't think thats too important.I think the clearance at the hot end should be minimal,and possibly the same at the power piston.The only problem with dead space is compression of the airbetween hot and cold ends. Sound as though you'v got two recruits,hope they stay interested,because kids like them seem to be a rare breed these days.Meccano and pulling things to bits(and tring to get them going again),and then my grandpa giving me a Mamod steam engine is what started me at a similar age. On the mock up of the Ross linkage I'v got 1/2" crank throw,the con rods are 2 1/2" apart and the pivot point is 1 1/4" from the crank ie same distance crank to pivot/pivot to con rod.the stroke of the pistons is 11/16".I was showing the mock up to a friend who is an engineer,and we were wondering why no one had built an IC engine with a linkage like this.I must have a look on Google to see if there is anything there.Ian s c |
| Mark Smith 3 | 08/12/2009 18:18:30 |
175 forum posts 36 photos | It's a shame ME can't republish some of these earlier articles by Ross and Urwick as (Ross particularly) has a great deal of technical information in table form, I'm sure there would be a lot of interest.
Don 't know about IC engines with Ross yokes but according to legend some steam engines used a similar device. I wonder if two ross yokes set to balance each other would prove to be a smooth runner in an IC engine or even a multi cylinder Stirling.
Mark.
By the by it would be great to hear what others are up to  |
| Ian S C | 09/12/2009 10:26:25 |
7468 forum posts 230 photos | Had a bit of a look on the web this PM but couldn't find anything about IC engines and yokes,didn't get that far, kept getting side tracked.Every now and then there have been hot air secial issues,but that does'nt help new guys interested in making a start in the hobby,so I'm with you,a bit from the past maybe.If multi cylinder engines didn't balance out,a balance shaft could be the answer,thats what Andy Ross uses.That system was also used I think in the V4 engine in the Ford Transit Van,and has been used in other engines.I'v started hunting out bearings for my Ross yoke motor,got 2 zz bearings with 7mm borethat will do nicely for the main crankshaft,think I'v go a bearing for the crank,still not sure whether I need ball race for the big ends,or the pivot rod,quite sure the latter will be ok plain.Ian S C |
| Gordon W | 09/12/2009 11:58:25 |
| 2011 forum posts | Hi all, have got started on my big motor, 100mm i/d heateretc. Dont think Ford V4 had balance shaft ,they did have a self destruct crankshaft. Lots of modern motors have balance shafts. I have an idea that some marine diesels had Ross type links. I would think there is to much sliding friction for high speed motion, but could be very wrong. |
| Ian S C | 09/12/2009 12:34:14 |
7468 forum posts 230 photos | Wont argue about the ford.I would have thoughtthere would be less friction ie no side thrust on the pistons,only problem at high speed could be inertia in the exra weight in the system of the yoke its self.The action of the mechanisim looks interesting regardless.Another one that looks interesting is the rhombic drive but thats a long way of for now |
| Mark Smith 3 | 09/12/2009 18:05:46 |
175 forum posts 36 photos | good to hear from you, Gordon. That engine is a monster by the sound of it.
Mark |
| Ian S C | 15/12/2009 11:05:35 |
7468 forum posts 230 photos | Mark you wouldn't happen to know if you can buy the little ball races that fit on the end of wood router cutters.Got to go to town Thurs for cap screws,and a new bearing for the top of the spindel on my vert mill,so I'll look at some wee bearings for the Ross Yoke motor.Gordon what are you going to heat your motor with?Ian S C |
| Gordon W | 15/12/2009 14:52:04 |
| 2011 forum posts | I'm planning to use gas blowlamp initially for heat, but finally, and if it works, a coal fire, just for a bit of realism, hope it will power a small genny or water pump, just to answer wifies " what use is it". But this is a way off yet, I've just made the end flange from 13mm sq. and weled and turned. Had to make a large steady to do that, etc. etc. |
| Mark Smith 3 | 15/12/2009 18:11:03 |
175 forum posts 36 photos | sorry, Ian, I don't; maybe smiths city they sell router stuff |
| Ian S C | 16/12/2009 08:29:56 |
7468 forum posts 230 photos | At Homebush during the open days I was talking to a young couple who had just bought a Canadian made hot air fan to sit on the log burner and circulate the air,I forgot to find out their name because if they lived close I'd like to see it.Gordon I immagine that your motor is vertical,hot end down,if you go gas instead of coal,or interchangable with it,a camp cooker burner is the easiest.It would be more portable if you take it out for a demo,I take mine to A&P shows etc.I was cleaning up some scrap steel for my latest motor,and things weren't sounding quite normal,so I had a look at the top bearing,it has caused trouble before,it spun in its housing,but loktite bearing lock cured that.It must have worked because it was a hard job pressing it out(it fell out before I glued it in).Ian S C |
| Mark Smith 3 | 16/12/2009 08:58:02 |
175 forum posts 36 photos | My Grandson's cousin's (Grand nephew?) engine is running. It goes well and fast with a gas flame but not so well with meths. I think I will thin down the hot cap some more and reduce the thickness of the leather seal as I think it is causing too much friction. Now I have proved that it goes I can start building the cooler, burner, burner housing and add a generator to give it something to do. This engine is a Beta design and has a 25mm bore and 20mm stroke. The displacer stroke is 30mm giving the swept ratio of 1 to 1.5.
I have the parts I need to start making a rev counter namely an eighty three tooth gear and a matching worm gear from a junked video recorder (both plastic). The shaft in the worm gear is 1/8 steel. I am going to follow, within reason, the design in James Rizzo's book: Modelling Stirling and Hot Air Engines. Then build the torque arm with weights etc.
I am hoping this kit will show the two boys that the maths they learn at school has some purpose for them if it relates to something of theirs as they test their engines to find out how much power they produce.
When I have done all that I can go back to my own engine projects.
Mark |
| Gordon W | 16/12/2009 09:56:41 |
| 2011 forum posts | My motor will be horizontal cyl., I feel there is less heat going to the cold end that way. It's based on old designs, very basic and simple, but with ,hopefully, better materials.. Change of tack.- Back in early 70s, I saw a hot air engine at a steam rally, this was driving an old mangle, the owner gave me a sketch about how it worked, I've lost it. From memory it was something like a Robinson eng, but it had a very tall chimney, about 6ft, which ,according to the owner was lined with copper gauze, and this was the critical part of the engine. Has anybody any idea what it was? I can't find anything like it ontnet, may be bad memory. Wish I'd taken more notice now. At the same rally the then all new range rover was being demo'd, and a chap had a sports car with a rear mounted steam engine fitted, very impressive |
| Ian S C | 16/12/2009 11:25:23 |
7468 forum posts 230 photos | Gordon W my best(second built) is horizontal,its in one of Marks photos,its based on James G.Rizzo's Dyna it has 1 3/4" bore,it has a camper stove burner.A more efficient type is a ring burner that surrounds the hot end,but I'v only used these on vertical engines with the hot end at the top.The engine with the copper gauze lined chimney sounds interesting,must see if I can find out anything about it.Ian S C |
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All Forum Topics > Beginners questions > Hot air and stirling engines