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Well I know it's 3.2% per volume, I have done the math myself during chemistry class... So are.you telling me I just have to 3.2% x pressure = fuel pressure ?
Edit: ok, I'm good now, I got it stupidly simple.
I would just substitute the 3.2% for propane in the equations from 'Part 2' in the Hybrid Fueling 101 thread.
So... VP = (100*10)/0.958(100*10) VP = 44 cubic inches PC = 0.44*14.7 PC = 6.44 psi would become (by subtracting 0.032 from 1): VP = (100*10)/0.968(100*10) VP = 33 cubic inches PC = 0.33*14.7 PC = 4.85PSI Thus; 1x mix of butane = 0.485PSI I assume that's how one would calculate it anyway. Remember that the n mix pressure of butane is dependant on atmospheric pressure so substitute the 14.7PSI for your local atmospheric pressure.
The math for butane works out to be 0.47481 PSI/mix.
Basically, it works like this... simplified. 14.7(1+0.0323)14.7 You can substitute 0.0323 for the stoichiometric fuel/air ratio for any fuel and get the PSI/mix for that fuel. For propane, it works out to 0.6174 PSI/mix. For propylene, it works out to 0.68649 PSI/mix, etc., etc. EDIT: Crowley, I have some problems with that method. If SB15 dropped by that would be great. Basically, SB15 is treating stoichiometric ratios like this... 4.2% of the total composition is propane, with 95.8% of the total composition being air. When, in fact, doing stoichiometry, you do dimensional analysis, and find that 4.2% of the air you're using in your reaction is the amount of propane to react completely with that air... so 4.03% of the total composition is propane, and 95.97% of the total composition is air. I wish SB15 would pop by... I believe we talked about this in spud chat one night. Although, in practice, the difference isn't that noticeable, as you, SB15, DYI, and a few others have more than proven. Not trying to be a knowitall or anything.
Last edited by mark.f on Fri Jan 25, 2013 7:24 pm, edited 1 time in total.
Yay, thank you ^^
@MrC: what? The atmospheric pressure is different from your side of the world.than my?
Mark is correct, the equations in my thread use the fuel percentage as a fraction of the total molar quantity of gases, when it should actually be a fraction of the vessel volume. I've been meaning to update the thread for at least 2 years now, but other things have shifted my focus away from spudding.
You can still use my equations, but to obtain exact results you will need to use 4.03% for propane, 3.10% for butane, 4.46% for propylene, etc.. In any case, it's not likely to make much of a difference, as discrepancies between calculated values will almost always be offset by practical measurement error. Also, good day to all SF members, it's been a while.
People should not be afraid of their governments. Governments should be afraid of their people.
@mark.f
I'm pretty sure my adjustment for altitude is the unaccounted variable. Here is my math. x=propane (psig) y=manometer height difference (inch)
*does not include SB15's "it should actually be a fraction of the vessel volume" In other news... Added 2x worth of propane, then the manometer slowly recedes back to zero. Then I added ~13psi, 2x worth of air, click the ignition and boom! In essence this incurable leak adds this phantom variable I'm not accounting for. Next chance I get I'm adding an air meter, same construction as a propane meter, so that I can speed the process. AKA the propane/air mixture can leak equally. It is a mess, amid my ramble I'm realizing no one is reading this far so this is end of this post...
I am. So are you counting down the leak time then firing? Equal shot regularly...
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Haha well I just meant if you weren't at sea level. Even though I'm at sea level, atmospheric pressure still fluctuates about 0.5PSI between the average of summer and winter months. Daytoday it's very consistent but the difference between the record high and record low is more than a whole PSI in Auckland (which would throw off a 10x mix by up to 10PSI).
You know what? I'm going to stay with my syringes, I can't find some decent gauge and portable gas(any kind) with threads that I can use to build a meter isn't sold here anyway :l
25.6 inch height difference = .925 psi propane
15 psi air Hail to the potato launcher god(s)! It works every time! Also made a projectile out of 3/4" pipe. Gnarley looking, but cheap.
 
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