Author Topic: Tiny Stirling Engine (Read 49272 times)

NickG · « **on:** November 20, 2010, 12:21:28 PM »

I've been to the doctors and diagnosed with

again!

This is annoying as I now have 3 projects on the go - not counting the bigger ones!

The other annoying thing is that my projects always start off as a quickie but don't end up that way - this time it was Jan Ridder's fault again! He recently posted his Micro Stirling Engine on his website - I had to see it so asked for the plans, which he was very kind to send to me. The problem is, I just don't like making stuff from other peoples plans blindly! It never seems to suit my materials or processes so I have to change things - but I probably go too far.

This time I've tried to combine the best ideas from Jan's and another engine I found on youtube - see below:

http://heetgasmodelbouw.ridders.nu/Webpaginas/pagina_stirling_1_euro_10/frameset.htm

Mine is going to end up a little larger than these two mainly to make things a bit easier for myself and what I have to hand, it should also give it a slightly better chance of running.

I have done the CAD model which took a bit of working out but have not yet done the 2D drawings. Please see attachment for the 3D model. I did calculations to ensure the ratio of swept volumes between displacer piston and power piston are almost the same - this is quite important as it largely governs the temperature difference the engine can run on, of course there are a lot of other factors but I think this engine should work.

Need to crack on and produce the drawings over the next few days and get cutting some metal - otherwise I'll have projects coming out of my ears!

Nick

shoey51 · « **Reply #1 on:** November 20, 2010, 01:43:23 PM »

this will be very interesting to watch

cidrontmg · « **Reply #2 on:** November 20, 2010, 05:29:55 PM »

Hi Nick, seems we´re both making Stirlings. Mine will be bigger, yours is really small. I d/loaded your CAD model, the yellow parts are obviously brass, flywheel seems to be aluminium. How about the pistons? Graphite power, I guess, but what´s the displacer made of? And the displacer cylinder? Ball bearings, I assume? In the video, the flywheel seems to be acrylic(?).
I might try an LTD Stirling sometime soon, but not quite this small

In HMEM, there´s an ongoing build of an alpha-type Stirling that refuses to run. I must be daft, but I can´t see why or how it would run...

Although I know that (some) alpha Stirlings DO run...
Looking forward to many pictures, I´m going to watch this both eyes wide open!

sbwhart · « **Reply #3 on:** November 21, 2010, 02:00:55 AM »

I like that Nick

I may have a go at one when you've got the drawing completed.

Stew

Stilldrillin · « **Reply #4 on:** November 21, 2010, 06:44:42 AM »

Looking forward to this project Nick.

Good luck!

David D

NickG · « **Reply #5 on:** November 21, 2010, 07:43:54 AM »

Thanks for the interest guys.

Is still have a couple of issues to sort out with the design. The crankshaft on mine is turned from a piece of solid brass - it might be a bit heavy but I can balance the assembly later by adding mass to 1 side of the flywheel. Hopefully, as my cc is larger, the engine will have enough about it to turn it over. It shouldn't be difficult to machine but I'll have to do things in the right order as it will not have much structural integrity once I start cutting the journals. The other problem doing it from solid is how do you get the big ends on?! Jan's plans suggest putting small slit at the end of the con rod into the big end hole, the rod is that thin you can simply bend it, push it over the crank journal and it'll spring back - I don't really like the sound of that so was racking my brains to think of something else - I can't think of something simple so it seems Jan's idea is a good one.

You're right about all the materials Olli. The displacer is supposed to be balsa wood (I know, the colour is wrong!) but I might have to see what else I have that's suitable - might have some balsa somewhere. I think the flywheel in the vid looks like acrylic. I've found some plastic for my displacer cylinder - top off sun cream, might work, might not, if not I'll have to do what Chris suggested and go around tesco's with my digi vernier

Ade kindly sent me the graphite for the piston so I'll be attempting that.

I'm not sure what an Alpha type engine is Olli - I was up to speed on this sort of stuff but have forgotten, would have to read up again! Is it the type where the displacer makes a seal too rather than allowing the air around it? I think you need a lot of heat for them and they usually have a low ratio of swept volumes to keep everything as efficient as possible? Or am I thinking of something else?

I'll have to get on with the drawings later but I won't post them until I know it works!

Nick

madjackghengis · « **Reply #6 on:** November 21, 2010, 11:32:48 AM »

Hi Nick, interesting build, funny you should only have three projects going, are you ever going to be a serious modeler?

A beta Stirling is one where the power piston runs in the same cylinder as the displacer, and is probably the most efficient, it certainly is in large scale. An alpha type is one with a separate displacer cylinder and power cylinder, with the two connected, and easiest to make LTDs since they tend to have large diameter displacer cylinders, and short strokes, with long stroke, hence high torque power pistons, to make them work well at low differentials. I only know this because I'm starting one of each at the moment, and am still gathering materials.

mad jack

NickG · « **Reply #7 on:** November 21, 2010, 12:12:34 PM »

Hi Madjack,

I said I wasn't including the larger projects, mainly because it just depresses me - can I never finish anything?! I might as well mention them now though, they include the refurbishment of a 3 1/2" gauge locomotive (same as Stew's as it happens), refurbishment of a 4 1/2" scale wallis & stevens simplicity Steam Roller, building of a 5" gauge sweet pea locomotive and not a model but the restoration of a 1989 Ford Escort RS Turbo - all work in progress but haven't done much with any of them for a long time. Every time I look at any of them more seriously, I find something that makes them become an even larger project

Thanks for explaining the different stirling cycle engines. I have made 1 stirling so far to my own design, it was an alpha type engine with the cylinders at 90 degrees to each other enabling use of the same crank.

I remember coming across another type of engine though, I can't remember the designation, still two cylinders but they both have air tight pistons - can't quite remember how they work, willhave to have a look. THink there is a regenerator in the middle and somehow both pistons provide a power stroke?

Nick

Brass_Machine · « **Reply #8 on:** November 21, 2010, 09:50:30 PM »

Wow that is a tiny Sterling. Best of luck on this one Nick. I know I will be watching.

Eric

madjackghengis · « **Reply #9 on:** November 22, 2010, 11:37:39 AM »

Hi Nick, there is a "Ringbom" Stirling, which has a piston which moves just the displacer, and has a separate power piston which moves according to the pressure differential, and there is a "resonance" or "acoustic resonance" type where it has a single piston, a heat chamber with good insulation from the cylinder and piston with the cylinder well cooled, and relies on a "resonating pressure pulse" established by the heat raising the pressure, and the power piston setting up a pulse, which will settle into driving the piston at the resonant frequency of the pressure wave in the closed cycle, as it alternates between pressure and temperature change, as per the first law of thermodynamics, I believe, which says in a closed system, the pressure of a gas will be directly proportional to the relative temperature, so the piston changing the volume allows the temperature to turn into pressure when the volume is reduced, and pushes the piston out, which increases the volume, allowing the air to cool, with the excess heat carried off by the mass of the cylinder, piston and the rest of the "cool" end of the engine, which takes it below its original pressure, so it expands faster when all the air is pushed into the hot end, and raising the pressure again. The phase shift takes place in the transfer of the heat to pressure, and the change of pressure with the "loss" of heat when the piston has been moved, and has lowered the pressure by increasing the volume, and at the same time, losing some of the energy of the heat also through transfer, causing the resonant effect which acts in place of a displacer. This engine seems to work by applying the same principle of a "hydraulic ram", pumping system which uses the inertia of running water to establish a resonance, and pump by just changing the pressure in a closed chamber with valves to bleed off excess water, and keep a resonating pressure change continuing and the inertia of the water actually doing the pumping. There is a video of this form of single piston Stirling among the videos available at the beginning of this post. It has taken a lot of mind bending to get around this idea and make it make sense, but having seen it work, it must make sense.

mad jack

arnoldb · « **Reply #10 on:** November 22, 2010, 12:53:07 PM »

Count me in on the peanut gallery crowd Nick

Have to get around to an LTD myself at some point... A "normal" sterling as well!

Kind regards, Arnold

NickG · « **Reply #11 on:** November 22, 2010, 03:12:36 PM »

Thanks for the info Madjack, I've often been fascinated by the acoustic resonance and thermal lag type engines but have never made the effort to understand how they work! I will have to read your post a few times to get it to sink in. The type of engine I've seen isn't that or a ringbom though, it's more like the following link, except I didn't realise it was 'Rider' engine: http://www.stirlingengines.org.uk/work/cyc1.html

I think we're all getting confused with alpha and beta types - alpha is the sort I am talking about in link above, according to Wikipedia http://en.wikipedia.org/wiki/Stirling_engine (and that was the way I understood it). The beta, as you rightly said has the loose fitting displacer which displaces air from a hot end to the cold end and the power and displacement pistons are in the same cylinder. The gamma is the one with a loose fitting displacer but there are separate power and displacement cylinders which are connected, so that is the sort I have made before and is what this LTD will be.

Nick

ozzie46 · « **Reply #12 on:** November 22, 2010, 07:47:40 PM »

Good grief!!!! That thing is small. Don't sneeze or you'll never find it.

You people that can do this small stuff have my greatest admiration.

Nice going Nick.

I have enough trouble with the size of Elmers engines.

Ron

NickG · « **Reply #13 on:** November 23, 2010, 03:24:41 AM »

Thanks Eric, Arnold and Ron - but I haven't made an LTD myself yet, let alone this small! So the jury is out on whether I can do this small stuff or not yet!!!

If it doesn't work it'll get a metal displacer & cylinder and a blow torch underneath it!

Nick

madjackghengis · « **Reply #14 on:** November 23, 2010, 07:46:03 AM »

I've got to say, Nick, you've definitely got the right attitude

I like that, put a metal displacer in it, and fire up a torch!!

Sorry I forgot about the "big" projects you mentioned, I tend to forget about them because I have so many of my own sitting in the middle of repair, dis-repair, and mere contemplation. When I've got pictures of the different types, and their names under them, I can always tell what kind is which one, other than that, I'm easily confused once you get past the common ones, the alpha type, with the separate displacer cylinder and power cylinder, with the connecting hole, tube or line, and the beta, with both in one cylinder. I spent about an hour watching some of the fifteen or more examples in the link you attached to the beginning of this log, and have seen both the Ringbom type, and the accoustic resonance type running, as well as a whole set of ones I've heard of but never seen. It's quite a link to some very fine, and I mean fine, engineering. I think you'll get this one down just fine.

mad jack

NickG · « **Reply #15 on:** November 23, 2010, 11:27:15 AM »

Madjack,

I'm glad it's not just me, I knew it wasn't though - there must be so many unfinished projects out there, I bet some just an inch from completion of amazing models. But lots, like yours and mine in the middle of repair, dis-repair and occasional contemplation!

That's the problem with youtube - you click on something and then realise there are many others in the frame on the right, then when watching one of those, it brings up another 15! I love the Ringbom type engines, they are fascinating to watch! Last night was wasted on youtube instead of working on the drawings

I hope it goes to plan, am quite looking forward to it. I was planning to make two but I think I'll just go for one, otherwise I'll get bored and it'll be another part finished project!

Nick

andyf · « **Reply #16 on:** November 23, 2010, 01:55:18 PM »

On the subject of small Stirlings, here's a nano version:

Andy

NickG · « **Reply #17 on:** November 23, 2010, 06:15:10 PM »

That's impressive, watch maker?!

Nick

andyf · « **Reply #18 on:** November 23, 2010, 07:18:45 PM »

Quote from: NickG on November 23, 2010, 06:15:10 PM

That's impressive, watch maker?!

Nick

I don't know about that, but I believe he is very severely disabled. Goes to show that rather than giving up, you should just get on, do what you enjoy, and impress everyone with the results.

Andy

NickG · « **Reply #19 on:** November 24, 2010, 03:28:37 AM »

Wow! And the reason I don't get things done is mainly laziness - puts things into perspective.

I did actually make some progress last night - I 2D drawings for 5 of the parts, but have another 11 to go. The good thing is, many of them aren't complicated - I'll ~~probably~~ hopefully get another few done tonight then the remainder on thurs night ready to start machining on the weekend!

Nick

NickG · « **Reply #20 on:** November 29, 2010, 05:15:17 AM »

Got all the drawings done for the Tiny Stirling now and was planning to start machining over the weekend but as always, life gets in the way. Saturday I started painting the downstairs loo, Sunday the car broke down and won't start and today on the way to work the other car broke down and went into limp mode - nearly killing me, again! Only had it since August, was in the garage last week supposedly getting repaired for something that wasn't covered by the 3 month warranty - £250 later then today, of all days, it cuts out when pulling onto motorway. In my experience all I can say is, don't buy a Citroen and don't buy from Evans Halshaw.

A very pissed off Nick!

sbwhart · « **Reply #21 on:** November 29, 2010, 08:31:47 AM »

Thats a real bummer Nick luckily you weren't hurt.

Stew

Stilldrillin · « **Reply #22 on:** November 29, 2010, 12:57:39 PM »

Ohh, Nick!.
Very sorry to hear that.....

It's amazing how life gets in the way of the best laid plans.

Hope you're soon sorted, and back to what passes as "normal".....

David D

shoey51 · « **Reply #23 on:** November 29, 2010, 03:31:07 PM »

thats bad luck mate hopr you get it sorted soon and back to normality

NickG · « **Reply #24 on:** November 29, 2010, 06:33:06 PM »

Cheers guys, sorry, bit

but I started ripping bits off the little Clio today to try and find out what's wrong. I was thinking it could be the crank angle sensor so have taken that off and ordered a new one, but while I was on I thought I'd whip the spark plugs out and do a compression test, as it sounded like there was no compression when turning the engine over - with my heath robinson compression tester (a grandad special!) there was zilch on any cylinder - will have to borrow a proper one to confirm it though. Not quite sure what it could be - cam belt could have slipped round? but would expect to see something on the gauge - valves stuck open possibly? - will have to get the rocker covers off to have a look at that. Anyway, will leave it there as this could be a whole new topic but you get the picture!

As for the other car (citroen) it's just too complicated for its own good, am incredibly annoyed, they are charging me £85 to get a recovery truck to pick it up to "have a look at it" as far as I'm concerned it aint coming back, going to fight for my money back (or most of it) and try something else

As Stew said, no actual harm done though and I've finished painting the toilet so

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Author Topic: Tiny Stirling Engine (Read 49272 times)