High compression

Discussion on Stirling or "hot air" engines (all types)
camerart
Posts: 9
Joined: Thu Dec 15, 2011 2:39 am

High compression

Post by camerart » Thu Dec 15, 2011 2:55 am

Hi all,

I'm new to this forum, so hello.

I would like to know if anybody, has experience in the type of piston with a con-rod sliding though it, where a second piston can be mounted as in some Stirling engines, giving two stage compression.

I need to know if this type of piston is capable of very high compression ratios, as in Diesel engines 'say' 20/1?

Cheers, Camerart.

celinaaniston86
Posts: 3
Joined: Thu Dec 15, 2011 3:32 am

Re: High compression

Post by celinaaniston86 » Thu Dec 15, 2011 3:38 am

Actually, a variety of pressure and warm. That's why they have gleam attaches to help to start the engine when it's cool. The burning time is then established by when the fuel is shot instead of spark plugs.

Ian S C
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Location: New Zealand

Re: High compression

Post by Ian S C » Thu Dec 15, 2011 6:04 am

Don't think of compression ratios as in internal combustion engines of any type. In the Stirling engine the displacer has its prescribed amount of room to move, with a minimum amount of clearance at each end of its stroke, the passage between the two cylinders should be as small as possible (although this is not too important according to an article in Model Engineer 18th Feb 1977, by W.D. Urwick who linked the cylinders of a test motor with 6ft of rubber tube with little ill effect). The power piston should take the full length of its cylinder.
The important ratio is the one between the two cylinders, ie., 1.5 : 1, displacer to power, this is the ratio for a high temp motor, as the temperature drops, the displacer free space volume increases, as you will see if you look at the LTD motors (I think my LTD one is 20 : 1). The ALPHA motor is different, the ratio between the two cylinders is ! : !.
I have three BETA motors, ranging from 1 1/8" bore, 1 3/4" bore, and 2 1/4" bore, in these motors the displacer and piston clear each other by about 1/16". The middle size one is horizontal, the small one is vertical, with the hot end at the top, the largest onethe hot end is at the bottom. Ian S C

camerart
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Joined: Thu Dec 15, 2011 2:39 am

Re: High compression

Post by camerart » Fri Dec 16, 2011 4:08 pm

Thank you Ian,

I hope that we are not at cross purposes, regarding High compression of this type of piston combination. I am designing a different type of engine, and remembered the double piston in one cylinder arrangement. I realise that different styles of Stirling engine sometimes have this arrangement.

My question is, can the seal between the two piston be made to withstand high pressures, 20:1 for example?

Cheers, Camerart.

Ian S C
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Location: New Zealand

Re: High compression

Post by Ian S C » Sat Dec 17, 2011 3:46 am

Do you mean that the motor is pressurised to 20 atmospheres? If so the crankcase must be sealed too. Do you mean the power piston, and the displacer are in the same cylinder, ie., a BETA motor. Ian S C

camerart
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Joined: Thu Dec 15, 2011 2:39 am

Re: High compression

Post by camerart » Sat Dec 17, 2011 2:26 pm

Yes, there are two pistons, in one cylinder, and both are subjected to high pressure, perhaps 20:1 and perhaps more.

I need top know if there are examples of this arrangement being capable of sealing.

So, it's called a Beta motor, thanks.

Ian S C
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Location: New Zealand

Re: High compression

Post by Ian S C » Sun Dec 18, 2011 4:32 am

Yes this type of motor can be pressurised, The place that is a problem for sealing is where the crankshaft exits the crankcase, as the whole motor must be pressurised. Some people get around this problem by building a generator inside the crankcase, this is motored over for starting the motor, or as Andy Ross did coupled the crank to the flywheel with magnets. I have two motors basicly designed for pressurisation, but I'v yet to design seals for the crankshaft, I intend to use up to 100 psi maximum. Ian S C

camerart
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Joined: Thu Dec 15, 2011 2:39 am

Re: High compression

Post by camerart » Sun Dec 18, 2011 10:50 am

Thanks Ian,

I'll get experimenting.

Ian S C
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Location: New Zealand

Re: High compression

Post by Ian S C » Tue Dec 20, 2011 12:40 am

Ditto, arn't we all!! Ian S C

Ferraccio
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Location: Italy

Re: High compression

Post by Ferraccio » Wed Dec 21, 2011 10:01 am

Camerart,
1) The design is your. But more complex is the solution more difficult become extract energy.
2) Pressurization means that engine is closed in a shell, or with devices (compressors) that maintain pressurization: all type of engines can be closed in a shell, or beared by a compressor.
3) To define two stage... has no meaning; being as abovesaid (point one and twoo).
4) Of course the shell have to be dimensioned to bear pressure.
5) The differential pressure upside-downside piston is NOT simply in direct relation to the pressurization.
6) The differential at stop is zero, in running the differential is normally, for Stirling engines, very low; the advantage of pressurization is that the motor gas is more dense, and for so carrying more heat, and for so the pulse may be is (also if not directly) increased, dimensioning of running parts (sealings, bearings, crankshaft, rods), have to be dimensioned on said pulse, that may be is only a very low fraction of pressurization.
7) In S. Engine, for overpass the typical low differential of pressure (also in high temp. engines) are adopted short strokes and elevated speeds of rotation, similar as happens in turbines.

camerart
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Joined: Thu Dec 15, 2011 2:39 am

Re: High compression

Post by camerart » Mon Dec 26, 2011 3:46 am

Thanks for that explanation Ferraccio,

We are certainly at cross purposes.

I am designing a completely different type of engine and only wish to know, if the piston inside a second piston arrangement (As in some Stirling engines) can withstand high pressures, as in a Diesel engine? So the rest of the engine is not pressurised. I am particularly interested in the seal between the two Pistons, as I know a single Piston can withstand the pressure.

Cheers, Camerart.

Ian S C
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Location: New Zealand

Re: High compression

Post by Ian S C » Mon Dec 26, 2011 6:33 am

Camerart, I think you'll need to try and post a sketch of what you are designing, so that we can see what you are proposing, because what appears to be evolving to me does not appear practical. Ian S C

R-WIN DEVELOPMENT
Posts: 6
Joined: Sun Dec 18, 2011 7:53 am

Re: High compression

Post by R-WIN DEVELOPMENT » Mon Dec 26, 2011 9:00 am

camerart wrote:Hi all,

I'm new to this forum, so hello.

I would like to know if anybody, has experience in the type of piston with a con-rod sliding though it, where a second piston can be mounted as in some Stirling engines, giving two stage compression.

I need to know if this type of piston is capable of very high compression ratios, as in Diesel engines 'say' 20/1?

Cheers, Camerart.
Hi Camerart
You can use air cylinder with teflon piston ring like this . . best regart

[BBvideo 425,350][/BBvideo]

camerart
Posts: 9
Joined: Thu Dec 15, 2011 2:39 am

Re: High compression

Post by camerart » Tue Dec 27, 2011 6:31 pm

I'm afraid I can't show you want I'm thinking about yet, as it is in the first stages of thought. I am working on a novel type of Diesel/bio fuel engine. One of the posibilities is the double piston arangment, but it seems that I can't find whether it will take the high pressures, so I will most likely use a different way of compression as a solution.

Thanks, Camerart.

Ferraccio
Posts: 188
Joined: Thu Jan 27, 2011 10:57 am
Location: Italy

Re: High compression

Post by Ferraccio » Thu Dec 29, 2011 6:49 am

As is obvious, always remember that any device, machine, engine, to be a successful invention should be substantially simpler than the existing one ...-
Small complications are granted only in return for substantial large benefits.
For the oil (vegetal) diesel alternative "low technology" see Lister engine, with "today's technology" see the Elsbett engine.

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