Noob question - would these parts work?

Discussion on Stirling or "hot air" engines (all types)
Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Noob question - would these parts work?

Post by Blaf » Fri Mar 02, 2018 3:19 am

Hi guys and gals,
I'm thinking about building a larger alpha stirling for exhibition at one post-apocalyptic (of that stylized kind - Mad Max/Fallout style) event.

Since i'm pretty tight on the budget and also have no access to any machining tools, i was wondering if building a stirling from ready-to-buy stuff found on the internet would be feasible (also it would better fit visual settings of the event).

(i'm sorry for providing links in czech, i was looking for local supplies)
I found this 299mm diameter barrel, which i would like to use as a piston.
Then inserting this barrel in 300mm smooth stainless air conditioning tube serving as a cylinder (and it's extension also as a hot cap).
And then using temperature resistant low frcition teflon tape to seal the piston.

The plan is then to stick the hot cylinder into some kind of wood burning rocket stove, and submerging the cold cylinder into water.

Considering things stated above, i would like to ask you - would you expect these parts to work? Or am i on the wrong track here? Is the teflon tape able to lower the friction enough? Am i crazy?

Many thanks in advance!

Alfista
Posts: 91
Joined: Thu Feb 18, 2016 9:14 pm

Re: Noob question - would these parts work?

Post by Alfista » Fri Mar 02, 2018 7:55 am


Blaf, you may be able to make them work with some handwork. Personally, I would avoid making a power cylinder from stainless steel, but perhaps I have misunderstood you. If you are considering this as the displacer and displacer chamber, then the tolerence is much too close !

Perhaps you could make a makeshift lathe such as the one built by Matthias Wandel :

[youtube][/youtube]

Otherwise, if you are looking for "off the shelf" components, you could consider an Airpot cylinder to build a small engine. To build a very large engine as the one you are looking to make. Unless you have machine tools, you may want to look at constructions by Approtechie Attila Blade and other similar other makers for ideas on making large diaphragms or bellows, etc.


Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: Noob question - would these parts work?

Post by Blaf » Fri Mar 02, 2018 11:26 am

Hi, thank you for the reply.

You understood correctly, i planned using stainless tube for both hot cap and power cylinder. I choosed such tube because its quite cheap.
What would you recommend using for power cylinder instead? Or maybe could you elaborate more about why is stainless steel bad choice to statisfy my curiosity?
Btw, the engine is supposed to be alpha, so two pistons and no displacer...

Ive checked Airpot and while their glass/graphite pistons are really nice, they are quite expensive (mind you, we are pretty poor here in central europe :)

I never thought of making diy lathe, thanks for the inspiration!

Ian S C
Posts: 2154
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Noob question - would these parts work?

Post by Ian S C » Sat Mar 03, 2018 3:43 am

A power cylinder could be made from an old wet sleeve from a truck or tractor engine, this might give you 120/150 mm bore (there's one under my bench). It's possible your scheme could work, but how round is the stainless AC tube. Adapt your design from a working motor.
Ian S C

Alfista
Posts: 91
Joined: Thu Feb 18, 2016 9:14 pm

some alpha engines have displacers

Post by Alfista » Sat Mar 03, 2018 8:01 am

Blaf,
some alphas have displacers and since you have not started building yet, I would encourage you to consider the possibility in your design. Usually, this has the result of moving the rings of the the hot piston a good distance from the heat. Directly heating the cylinder and piston is rather problematic as it increases both the prospects of friction as well as leakage and complicates the problem of lubrication. If these issues are not addressed, then, if the engine runs at all, it may either run when it is quite hot or when it is warming up but not under both conditions. In any case, the issues of the coefficient of friction and the thermal expansion coefficients are especially important in a heated cylinder. Rider (1905) dealt with this in two ways, he moved the sealing ring as far from the heat as possible and he also used a rather long displacer attached to one cylinder. I am not saying that things must be done this way. I am saying that these are important issues to resolve in order to build a successful alpha engine.

Stainless steel is relatively sticky compared to cast iron but it still could work. In any case, as long as the issues of thermal expansion and friction are addressed with regard to the cylinder and piston combination, then it can certainly work. Keep in mind that the hotter the cylinder and piston, the more difficult the job of lubrication.

Alfista
....

Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: Noob question - would these parts work?

Post by Blaf » Sat Mar 03, 2018 1:55 pm

Ian S C wrote:A power cylinder could be made from an old wet sleeve from a truck or tractor engine, this might give you 120/150 mm bore (there's one under my bench). It's possible your scheme could work, but how round is the stainless AC tube. Adapt your design from a working motor.
Ian S C
I was also wondering if the AC tube would be fine enough. Thanks for the tip, ill check if i can get some cheap engine sleeves, however that means ill have to find some other off the shelf item to be used as a piston :)

Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: some alpha engines have displacers

Post by Blaf » Sat Mar 03, 2018 2:11 pm

Alfista wrote:Blaf,
some alphas have displacers and since you have not started building yet, I would encourage you to consider the possibility in your design. Usually, this has the result of moving the rings of the the hot piston a good distance from the heat. Directly heating the cylinder and piston is rather problematic as it increases both the prospects of friction as well as leakage and complicates the problem of lubrication. If these issues are not addressed, then, if the engine runs at all, it may either run when it is quite hot or when it is warming up but not under both conditions. In any case, the issues of the coefficient of friction and the thermal expansion coefficients are especially important in a heated cylinder. Rider (1905) dealt with this in two ways, he moved the sealing ring as far from the heat as possible and he also used a rather long displacer attached to one cylinder. I am not saying that things must be done this way. I am saying that these are important issues to resolve in order to build a successful alpha engine.

Stainless steel is relatively sticky compared to cast iron but it still could work. In any case, as long as the issues of thermal expansion and friction are addressed with regard to the cylinder and piston combination, then it can certainly work. Keep in mind that the hotter the cylinder and piston, the more difficult the job of lubrication.

Alfista
....
I have to apologize, since it seems my poor english caused a misunderstanding - i was refering to separate displacer in my previous post, as i was under impression its called a "Heylandt crown" in alpha configurations, being attached to piston.
I am aware proposed teflon tape sealing is far from perfect, therefore i already plan to use pretty long 60-90cm) hot cap with displacer/heylandt crown in it. Separation of hot cap and hot cylinder is planned, using flanges with thermal insulation in between.

I should probably attach a picture of some sort, i understand my initial description is not thorough enough.

Regarding the stainless steel stickiness - do you think maybe some additional dry lubricant would help? Graphite powder comes to mind, i found out its quite cheap.

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Noob question - would these parts work?

Post by Ian S C » Sun Mar 04, 2018 1:53 am

You are right, the displacer type thing in an ALPHA motor is attached to the top of the piston is called a Heylandt Crown. It keeps the direct heat off the piston, and also has the regenerative effect that the displacer has in other types of motor. I would keep the length to 300 mm to 500 mm long.
Ian S C

Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: Noob question - would these parts work?

Post by Blaf » Sun Mar 04, 2018 4:57 am

Thanks for the tip Ian, glad to hear the crown could be shortened. Am i correct assuming the hot cap itself should be shortened accordingly, containing as low dead volume as possible?
This leads me to another question - is there some rule of thumb for crown side clearance to hot cap (e.g. in order to not restrict the air flow)? Or should i also keep the clearance just small enough to avoid contact?

Btw, thank you both for your patience with me, i really appreciate it :)

Ian S C
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Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Noob question - would these parts work?

Post by Ian S C » Mon Mar 05, 2018 1:27 am

I'm not too sure about the clearance in a motor that big, a gap of 2.5 mm/3 mm sounds about right by me, I think maybe 4 mm/ 5 mm for end clearance. Really if you are going to build to this size you should have a machine shop with at least a lathe, and quite a big one at that.
Ian S C

Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: Noob question - would these parts work?

Post by Blaf » Mon Mar 05, 2018 3:18 am

Ian S C wrote:I'm not too sure about the clearance in a motor that big, a gap of 2.5 mm/3 mm sounds about right by me, I think maybe 4 mm/ 5 mm for end clearance. Really if you are going to build to this size you should have a machine shop with at least a lathe, and quite a big one at that.
Ian S C
Unfortunately i don't have access to any machine shop. For this reason i was hoping i could build the engine from off the shelf parts using just welding, screwing, grinding and gluing :)

Alfista
Posts: 91
Joined: Thu Feb 18, 2016 9:14 pm

I agree with Ian

Post by Alfista » Mon Mar 05, 2018 7:57 am


To quote the Sherline Tools motto "Think big and build small". If you plan on building such an ambitious project, you should be willing to build up to it and one way or another build or borrow the tools necessary to accommplish it. If you can build even a small alpha engine, then you can build a lathe such as the Wandel lathe. He publishes plans for it and even shows how to build a 4 jaw chuck. If you can build a small lathe, then you will have the knowledge to build a large one. An engine of the size that you are considering is a serious challenge but I believe that you can do it if you build up to it. Have you already built some gamma engines ? Ian is also right that it may be easier to build a multicylinder engine. Have you seen the engines of Approtechie or those of Attila Blade ?

Alfista


Blaf
Posts: 32
Joined: Fri Mar 02, 2018 2:50 am

Re: Noob question - would these parts work?

Post by Blaf » Mon Mar 05, 2018 9:04 am

To be honest, so far i only managed to assemble two small stirling models from premade parts :)
Ok then, if you both say this would probably be bigger than i could chew, considering my lack of essential knowledge/skills, i will rather rather start with something smaller. Thanks for the advice.

I think i have probably seen all the engines that are there to be seen on internet, so i'm aware of the work of these guys as well :)

Ian S C
Posts: 2154
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Noob question - would these parts work?

Post by Ian S C » Tue Mar 06, 2018 3:02 am

I have the feeling that you might end up disappointed tying something that big. My biggest one, a BETA has a 2.25" bore. But this ALPFA with 35 mm bores is just about as powerful, and will power this mechanical hacksaw with a Junior hacksaw blade (it really does cut steel ----- slowly).
Ian S C
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Blaf
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Re: Noob question - would these parts work?

Post by Blaf » Tue Mar 06, 2018 6:50 am

Actually the reason i intented to go that big is to have higher tolerance to imperfections that would inevitably come considering my construction options. And maybe still have some power left to light a bulb or charge a radio :)

I've already seen this engine of yours in other threads. Very nice indeed. Is it more powerful because of simply being alpha, or did you manage do integrate some construction improvements?

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