Critical Dimensions For Mixing Venturi?

Hello. Does anyone know what parts of a gas inspirator (venturi) primarily affect the fuel/air ratio? I've tried searching high and low
for the answer to this and can't find it anywhere. It seems like a black art or something.
See, what I'm doing is building a reproduction of a pest scaring device which makes a loud noise to scare away birds and animals from crops, just in case anyone was curious. The goal is to have an adjustable fuel/air ratio to vary the flame speed. This changes the "tone" that is produced. Maximum flame speed occurs when the mixture is stoichiometric and tapers off on either side. I figured someone on here would know about this because sometimes blacksmiths make their own custom burners.
Thank you, Robert
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Yeah. :/

Cool question! :)
Along the same lines I'd like to read about carburetors where the author really knows his stuff. Already read the "common" books on the subject. ...or should be "skirting" the subject?
I read my "yardsale" Encycolopedia Britanica from the mid 50's about flame and flame fronts etc first-thing then went to researching it further. Never ran across anything that was anywhere near as good as the first.
No kidding.
Suspect you need to look for "old" infomation.
Either way, post your findings here, so we can read it too, ok? :)
Alvin in AZ
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I believe I have found what I was looking for thanks to help from someone in alt.crafts.glass. It's called the North American Combustion Handbook and is available from amazon.com.
(Amazon.com product link shortened)
Cheers, Robert
snipped-for-privacy@XX.com wrote:

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Cool thanks! :) I believe I'll be able to borrow it from the UofA library. Anybody going for the $15 copy? :)
Alvin in AZ
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snipped-for-privacy@XX.com wrote:

Could you let me know whether it has the info I'm looking for if you get it? Some are saying it doesn't and others say it does.
Thanks, Robert
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Saw that it was even cheaper on Amazon lately so bought it. (ain't got it yet)
The sales-pitch sure makes it sound interesting. ;)
Alvin in AZ
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Anyone get their Combustion Handbooks yet? Does it have useful information about the orifice angles?
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Not yet, it's on its way tho. :)
Alvin in AZ
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Looks to me like it's got just about everything covered. :) Anybody else got a copy?

Never was all that sure what it was that was being looked for. Looks like it covers different types of orifices, placement and effect etc.
It's for sure geared toward industry just like ASM's metallurgy books, a guy has to just do his best to understand the material and apply it to his own needs as he goes. :)
Alvin in AZ
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Stumbled upon this the other day, may be a pointer to further research: http://www.aeronautics.ws/blunder5.html Perhaps you could find a trial version of a CFD (computational fluid dynamics) program to play with? --Glenn Lyford
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The Lightning Stalker wrote:

The gas accelerator has an effect on fuel economy, however the control valve and regulator play their part also.
Anyway, the following may help :-
Accelerator orifice ID    Burner Tube ID .031"        1/2" .031"-.038"    3/4" .044"-.048"    1" .054"-.064"    1 1/4" .064"        1 1/2" .070"        2"

I'd love to see some pictures of this device :-)
Regards Charles
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http://silenceisdefeat.org/~lgtngstk/Sites/Projects/Propane_Cannon_Noisemaker/Propane_Cannon_Noisemaker.html
Yhea, that's the feeling I get too. I just looked in a World Book encyclopedia from 1928 but still no luck. ;^_^;
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The Lightning Stalker wrote:

You might try something on jet engine design. What you're describing sounds a lot like a simple ramjet, so you might want to look into that area for general math parameters. Good luck...
Charly
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I believe I have finally hit paydirt on this, if anyone's still interested.
http://silenceisdefeat.org/~lgtngstk/Sites/Piccies/Burner_Success.jpg
I got to thinking that as the gas comes through the orifice, it is bent sort of the way light gets bent through a lens. The angle which it comes out would make more or less air get mixed in. Part of the idea comes from a patent for a "Punched orifice gas inspirator" where it says, "the ratio of injected primary air to fuel in the mixture will be proportional to the cosine of the injection angle". The other part comes from how most commercial orifices have a taper from one end to the other. The angle of the taper seems to affect the angle which the gas comes out and how it will mix with the air. Different orifices are longer or shorter because you need a longer one for a more gentle taper. The other thing which affects the mixture is the choke plate, of course.
Link to the patent: http://www.google.com/patents?vid=USPAT4156591
It's a lot easier to vary the choke plate opening than the taper of the orifice. So for the experimental burner, I needed as much air in the mix as possible from the orifice alone so that mixture control can be varied as much as possible using the choke plate. Also I have no idea how they can machine those tapers into the manufactured ones. So what I did was have a 90 "taper". How then to get a 90 taper? This might be hard to visualize but really it's extremely simple - just a thin piece of metal at the end with a small hole in it.
--------| --------|
This looks more like a true orifice plate. It also mixes the gas very well. I'm still not 100% sure if this is what is actually going on. I'm still wondering if that book has more information on this.
Cheers, The Lightning Stalker
The Lightning Stalker wrote:

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If you look at a mig tip, a lot of the work is done for you.
However I like to grind the tip so it looks like a bullet, this helps the air/gas mix.
Regards Charles P.S. THe gas looks like it's coming out pretty slow from that burner.
The Lightning Stalker wrote:

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Chilla wrote:

Mig welding just uses inert gas though.

Yes, it is! The gas at the orifice is under 1/2 psi.
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The Lightning Stalker wrote:

The point being is that mig tips are perfect for an accelerator.
The flame never touches the copper accelerator, and mine never get hot even after 4 hours of running at 300kpa :-)
I like to make tips on occasion for specialty jobs, but if I don't have to...
Regards Charles
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