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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.
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.
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 know-it-all 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.
I'm pretty sure my adjustment for altitude is the unaccounted variable. Here is my math.
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...
When life gives you lemons...throw them back they suck!
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. Day-to-day 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.
I hadm issed this working, good job
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