displacer and power piston proportions

Discussion on Stirling or "hot air" engines (all types)
Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

displacer and power piston proportions

Postby Shaysi » Wed Jan 25, 2017 2:44 am

hi everyone!
i am new here and almost got drawn with all the info around here...
my question is pretty simple..
there is any guidelines about the displacer and power piston sizes?
my motor should work with 350~500 degrees celsious on the hot side...
tnks!

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: displacer and power piston proportions

Postby Ian S C » Thu Jan 26, 2017 1:01 am

The standard ratio for a high temperature Stirling Engine is 1.5 : 1, swept volume of displacer to swept volume of the power cylinder. The displacer should be about three times its diameter in length.
The power piston can have a large diameter and short stroke, or a small (not too small) diameter and long stroke, as long as you stay some where near the 1.5 : 1 ratio.
Ian S C

thanh-cuibap
Posts: 147
Joined: Tue Sep 06, 2016 8:09 am
Location: Việt Nam

Re: displacer and power piston proportions

Postby thanh-cuibap » Thu Jan 26, 2017 6:31 am


Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

Re: displacer and power piston proportions

Postby Shaysi » Thu Jan 26, 2017 10:55 am

thanks! that was very helpful!
there is anywhey to predict the power i will get at the shaft? in general, there is anywhey to calculate it with exist motor? i have no torque meter..

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: displacer and power piston proportions

Postby Ian S C » Fri Jan 27, 2017 1:56 am

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You need Something like this, This is my torque arm on one of my flame lickers. You also need some way of measuring RPM, a non contact Laser tachometer is ideal.
Ian S C
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Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

Re: displacer and power piston proportions

Postby Shaysi » Fri Jan 27, 2017 5:55 am

yes i thought i will need torque meter but those tools very expensive and i dont know how to build one...

Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

Re: displacer and power piston proportions

Postby Shaysi » Sun Jan 29, 2017 4:34 am

Ian S C wrote:The standard ratio for a high temperature Stirling Engine is 1.5 : 1, swept volume of displacer to swept volume of the power cylinder. The displacer should be about three times its diameter in length.
The power piston can have a large diameter and short stroke, or a small (not too small) diameter and long stroke, as long as you stay some where near the 1.5 : 1 ratio.
Ian S C

hi lan,
according to your information, i noticed that the ratio of my Stirling (gamma) is 1:1...
I measured the strokes with caliber..
there is any influences of this on the motor power?

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: displacer and power piston proportions

Postby Ian S C » Mon Jan 30, 2017 2:48 am

If you can reduce the power piston's stroke to obtain the 1.5 : 1, this is probably the simplest way. The motor as is may run at high temperature with little power.
Ian S C

Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

Re: displacer and power piston proportions

Postby Shaysi » Mon Jan 30, 2017 4:00 am

Ian S C wrote:If you can reduce the power piston's stroke to obtain the 1.5 : 1, this is probably the simplest way. The motor as is may run at high temperature with little power.
Ian S C

you are right!
this is exactly what happened.. i need to reach temperature of 350 Celsius so it will start rotate...
but my final goal is to design Stirling engine that able to produce power of about 40 watt...
what do you recommend me to do with these displacer and piston ratio? i read in this forum that the more high of the ratio the lowest temperature needed to the hot end... is that affect the output power ?
thanks a lot!

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: displacer and power piston proportions

Postby Ian S C » Mon Jan 30, 2017 6:39 am

[My largest motor is a BETA type, power piston 2 1/4" bore x 1 1/4" stroke, Displacer 2 1/4" bore x 1 3/4" stroke, it can produce about 10 Watts at the crankshaft.
Ian S C
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Trevor
Posts: 169
Joined: Sun Nov 06, 2016 4:07 am

Re: displacer and power piston proportions

Postby Trevor » Mon Jan 30, 2017 11:43 pm

woo! That's a big engine Ian. The flywheels looked machined from iron.
Trev

Shaysi
Posts: 7
Joined: Sun Jan 01, 2017 5:55 am

Re: displacer and power piston proportions

Postby Shaysi » Tue Jan 31, 2017 5:17 am

ABSOLUTELY IMPRESSIVE...but yet didn't got answer...
if I want to produce about 40Watt...
what is the recommended ratio..? the more higher the better performance or to stay with 1.5:1 ratio?

Ian S C
Posts: 1970
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: displacer and power piston proportions

Postby Ian S C » Tue Jan 31, 2017 5:24 am

Not the flywheels are my usualls, a central disc 8 mm thick with the spokes cut in it and the hub fitted, then a 8 mm thick ring is bolted on each side. Where I was working up to a year or so ago we had lots of 160 mm discs of 8 mm hot rolled steel.
Ian S C

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Trevor
Posts: 169
Joined: Sun Nov 06, 2016 4:07 am

Re: displacer and power piston proportions

Postby Trevor » Wed Feb 01, 2017 2:56 am

Damn awesome Ian. They certainly look good. I am looking at 12"alloy ones that I can sand down (improvising) . Can't fit that size in my lathe as it will only swing 8". Trev


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