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Calculating ratios

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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Calculating ratios

Unread postAuthor: ROCK SOLID » Sat Mar 22, 2008 8:56 pm

Since i dont know much about combustion cannons, i was asking for good methods of measuring ratios i was looking at Wiki and i wanted to know

how you guyz figure out your ratios so i can use the same priciples to
measure my cannons preformance which i have no idea about.

So plz tell me how you guyz figure out your cannons ratio.
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Unread postAuthor: D_Hall » Sat Mar 22, 2008 9:30 pm

It's called "Chemistry" and in particular the "balanced equation for stoichiometric combustion."
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Unread postAuthor: mark.f » Sat Mar 22, 2008 10:32 pm

I think he's talking about volumetric ratios.

And, since I'm tired of this question, I will answer with cool-looking equations:

In that case, V<sub>c</sub>/V<sub>b</sub>=k, where k equals some constant, which is your C:B ratio. To calculate this ratio, use the following process/formula:
Image Definition of volumetric C:B ratio

Image Chamber volume, form of volume of a cylinder

Image The volume of the barrel takes same form

Image Composition

Image Simplified formula for C:B ratio

Just plug values into the last equation for your C:B ratio.

And, I will end this post with the ever-present reply: SEARCH!
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Unread postAuthor: jimmy101 » Sun Mar 23, 2008 2:22 pm

Another way to do CB ratio;

CB ratio = D<sub>c</sub><sup>2</sup> L<sub>c</sub> / D<sub>b</sub><sup>2</sup> L<sub>b</sub>

where
D<sub>c</sub> = diameter of the chamber
L<sub>c</sub> = length of the chamber
D<sub>b</sub> = diameter of the barrel
L<sub>b</sub> = length of the barrel

I'll leave it as an excercise for the reader to show that the fomula above is equivalent to markfh11q's equation;
CB ratio = r<sub>c</sub><sup>2</sup> L<sub>c</sub> / r<sub>b</sub><sup>2</sup> L<sub>b</sub>
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Unread postAuthor: mark.f » Mon Mar 24, 2008 4:24 pm


Well, since radius is 1/2 diameter, you can multiply each D by 1/2, factor out these 1/2's, and they cancel to equal one. Since the constant 1/2 exists in the numerator and denominator, they cancel.


Yup. I guess that's for people who don't want to divide diameter in half to get radius.
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Unread postAuthor: bigbob12345 » Mon Mar 24, 2008 4:35 pm

well i calculate themn myself but if you suck at math you can always use this
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Unread postAuthor: jimmy101 » Mon Mar 24, 2008 4:58 pm

markfh11q wrote:
Well, since radius is 1/2 diameter, you can multiply each D by 1/2, factor out these 1/2's, and they cancel to equal one. Since the constant 1/2 exists in the numerator and denominator, they cancel.

Yup. I guess that's for people who don't want to divide diameter in half to get radius.

Actually, it's for people who know that the area scales as the square of the diameter or the radius. Since pipe is sized in diameters there is no need to add two divisions to the problem. It is much easier to think of a 3" diameter chamber and a 1.5" diameter barrel using those numbers instead of 1.5" and 0.75".
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Unread postAuthor: mark.f » Mon Mar 24, 2008 10:41 pm

Sometimes diameter is prettier than radius, (i.e. dividing 1.625 by two adds another decimal figure). I wasn't trying to be sarcastic, I just said that's another way to do it without dividing diameter in half to get radius. There the same because multiplying by 2/2 is the same as multiplying the whole equation by 1, and multiplying each radius by two yields the diameter, so they scale the same.

And, if we really wanted to simplify it some more, we could rewrite it as:

<div align="center">Image</div>

Stop me! My photobucket's screaming!!!
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