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Right C:B Ratio For Aerosol

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Right C:B Ratio For Aerosol

Unread postAuthor: rustlerdude987 » Tue May 01, 2012 9:22 pm

like the title says what is the correct C:B ratio for a Aerosol like engine starter i keep hearing .8:1 is then 1.5:1 is correct. Which one is it?
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Unread postAuthor: jackssmirkingrevenge » Wed May 02, 2012 12:22 am

For "spray and pray" launchers where the mix is a bit hit and miss, 1.5:1 is the accepted ratio. If you want more power and more reliability, consider letting the lord syringe fuelling into your life ;)
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Unread postAuthor: jimmy101 » Wed May 02, 2012 4:25 pm

There is no such thing as the "correct CB ratio". 0.8 is generally the most efficient (but efficiency really is not important). 1.5 is a good trade off between performance (what you care about much more than efficiency) and chamber size.

But for a spray and pray none of that matters. The gun'll suck and the performance will blow.
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Unread postAuthor: rustlerdude987 » Wed May 02, 2012 7:50 pm

Wel than what is an ideal barrel and chamber size for spray and pray. The reason I went with a spray and pray is the ease of design and build. So what's the best camber length 3" and barrel length for 2.5"?
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Unread postAuthor: jackssmirkingrevenge » Wed May 02, 2012 11:44 pm

rustlerdude987 wrote:Wel than what is an ideal barrel and chamber size for spray and pray.


What jimmy was trying to say is that by going down the spray'n'pray route, you're basically saying "Fuçk proper air:fuel mix ratios, I'm letting fate decide!", so then worrying about correct C:B ratio seems a bit redundant.

The good old ordering-a-massive-triple-stacked-bacon-wrapped-grease-dipped-mega-burger-then-taking-a-diet-soda-with-it analogy ;)

If you want to maximise performance and reliability, meter your fuel properly. It doesn't add complexity to the build to fuel with a syringe.
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Unread postAuthor: rustlerdude987 » Sat May 05, 2012 12:26 pm

actually now that i look at this this seems really easy but i have one question is the ideal butane concentration always 3%
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Unread postAuthor: jimmy101 » Sat May 05, 2012 12:38 pm

Sort of. It depends on how you fuel. Technically a stoichiometric mix is either 3.12% or 3.22% depending on if the added fuel displaces air from the chamber (3.12%) or not (3.22%).

A very slightly rich mixture contains a little less energy but generally burns a little faster.
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Unread postAuthor: rustlerdude987 » Sat May 05, 2012 4:50 pm

so its that simple just find how much volume you have after the projectile is put in and multiply it by 3.22%
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Unread postAuthor: jimmy101 » Sat May 05, 2012 7:19 pm

Yep. With a syringe you would use 3.12%, for a meter pipe pressurized fuel 3.22%.
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Unread postAuthor: rustlerdude987 » Sat May 05, 2012 7:22 pm

perfect thanks for the help guys!
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