gamma stirling engine scale

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

gamma stirling engine scale

Post by Shaysi » Sun Jan 01, 2017 6:03 am

hello,
my name is shay and i build a gamma stirling engine by specific plans and its work good but
i need stirling engine that able to produce much more power...
my questions is:
1.where can i find good gamma stirling engine plans.
2.if there is any guiding recommended ratio to scale my exist engine so i can know the new output power..

tnks a lot!

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

Re: gamma stirling engine scale

Post by Alfista » Tue Jan 03, 2017 9:15 am


Shaysi,
most published plans are oriented to the gamma configuration. My preference has been to work from the plans of Rudy Kouhoupt published by Village Press. Rizzo in his two volume "Stirling Engine Manual" offers lots of detailed information on building but these fall short of what I would call detailed plans. In terms of determining output, it seems to increase roughly exponentially with size. As a rough estimate, Take the Pressure as something between 3.5 to 5 psi, Length= length of stroke in feet, Area of piston, and Number of revolutions. Let's say you have a 3" power piston with an area of 7.07 sq. in., a stroke length of 3.3125" in one direction x 2 = 6.625" or .55 ft., a Mean Effective Pressure of 3.5 psi., then P * L * A * N divided by 33,000 = indicated horse power. Subtract your losses for the actual horsepower. So 3.5*.55*7.07*100rpm = 1,360.975 / 33,000 = .041 ihp or 30W. So one would expect about 20 actual watts per 100 rpm. This can improve substantially with superior construction, regeneration, ultra low friction, high performance heater, etc.

Of course, the larger the engine, the more heat will be required however there are some nice advantages to building larger engines, namely the issue of piston leakage / friction becomes easier to deal with in larger sizes.

Alfista


Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: gamma stirling engine scale

Post by Aviator168 » Tue Jan 03, 2017 6:53 pm

The problem is to get your 3.5 psi across the entire stroke is every difficult. One better show a detail analyse before claiming an effective pressure. On top of that, as the engine gets bigger, heating/cooling gets more difficult.

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

Re: gamma stirling engine scale

Post by Alfista » Thu Jan 05, 2017 8:50 am

Aviator, you are right that 3.5 psi MEP is no small accomplishment.

When M.I.T tested a 6" Rider engine in 1896, they found a Mean Effective Pressure of about 3.48 (psi above atmosphere) on the pressure side of the stroke. Data on modern engines shows much higher MEPs but that is not at all the case for small, hobby engines where something like 1.5 psi or less might be expected.

I suppose that I should have framed my comments more carefully: At any given MEP and RPM, the power of larger engines increases more or less exponentially : at 1psi MEP and 100 rpm, a one inch engine should produce .29W, a 2" engine should produce 2.35W and a 3" engine should produce 8W. However, because of the ratio of leakage to piston surface area, it is quite likely that a larger engine built with the same materials and skill level will produce higher MEP than a smaller engine.

Alfista


Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: gamma stirling engine scale

Post by Aviator168 » Thu Jan 05, 2017 9:01 am

I get you Alfista. Makes sense.

Ian S C
Posts: 2221
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: gamma stirling engine scale

Post by Ian S C » Fri Jan 06, 2017 2:10 am

I find that James G. Rizzo's books give more than adequate building information, all I need is a rough sketch, with the main dimensions on it, we are making one off's, not a production line of identical motors(well that's me any way).
You just have to build as well as you can, and hope that you get better as you build more motors, and other bits and pieces.
Ian S C

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