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What does 1X, 2X, 3X, etc. mean?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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What does 1X, 2X, 3X, etc. mean?

Unread postAuthor: D_Hall » Thu Mar 20, 2008 9:38 am

READ BEFORE YOU ANSWER!


OK, nominally speaking 1X is a stoichiometric mix of fuel and air at 1 atmosphere pressure. 2X is at 2 atmospheres. 3X at 3. Blah blah blah.

But here's the catch....

Around here everybody assumes "1 atmosphere" is the same as ambient pressure, but it's not!

1 atmosphere is 14.7 psi.

If you live on the beach? Yeah, it's the same. But if you live in Denver, ambient pressure is only 12.3 psi. That's 2.4 psi - 16% - different. That's significant!

So... Is a "1X" load only achievable at high(er) altitude with a hybrid? I would argue that this is the case. I would argue that an "ambient pressure load" in Denver is actually a 0.84X load.

Thoughts?
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Unread postAuthor: psycix » Thu Mar 20, 2008 10:04 am

True.
Its about the same thing that most combustion cannons perform better at cold weather, since more fuel can be put in then.
More fuel (and oxygen ofcourse) = more power.

However, the air resistance is also lower in Denver. Not only during ballistic flight but also the air wich has to be pushed out of the barrel is less.
Though the amount of fuel that is less/more is vastly more determining the preformance of the gun. And I think that will probably outweigh the air resistance lowering the performance.


Luckely Im living BELOW sea level and arent there any mountains in this country and thus I wont have to worry about anything.
This all does make me think that the perfect weather to fire a combustion/hybrid is dry, cold and high-pressurized weather.


But, good thinking! This will certainly cause a significant difference in performance.
I hope people will give their ambient pressure when posting hybrid results in the future :)
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Unread postAuthor: BC Pneumatics » Thu Mar 20, 2008 11:25 am

I think it would come down to how you define "one atmosphere" when talking about the x mixes for hybrids.
If you define it as the pressure unit 1 ATM, then the poor folks in Denver come up a little short. Of course if you interpret it as meaning the ambient pressure, then people in Denver using 14.7psi increments would be ahead of the curve at a 1.16x mix. I do not know if this was differentiated upon creation of the "x system", but the first option seems to be the most obvious and intuitive.
Even if you use the former definition (the one I have always used for simplicity's sake) people at lower atmospheres can of course fire at 1x, they just cannot do so with a naturally aspirated cannon.

The great part is that if there is a problem, all we have to do is redefine the system to make it work properly, or be more descriptive. I think we are pretty much the ones that control these things ;)
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Unread postAuthor: Jared Haehnel » Thu Mar 20, 2008 1:14 pm

So I know this sounds very simple and I kind of like the sound of the "x factor" but why don't we take a few minutes to do the math and figure out what PSI the fuel and air mix is?
That way every one can see the results and get an idea of what pressures are capable of what. and those of you who use the BAR unit of measure post it in bars and I'll do the conversion...


Edit: Post the PSI no the "xfactor"
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Unread postAuthor: D_Hall » Thu Mar 20, 2008 1:57 pm

BC Pneumatics wrote:I think it would come down to how you define "one atmosphere" when talking about the x mixes for hybrids.

Well, the scientific community has already defined "one atmosphere" to be 1 atm (14.7 psi, 101300 Pa, etc...). "Ambient" is the accepted term for "whatever your current pressure happens to be."

The question is which of these scenarios does Nx marry itself to? Honestly, I don't think it's a question that's been definatively addressed. Or at least, i've not seen evidence of it (but am willing to be proven wrong).

In any event, I'll think I'll go with the "Denver is really a 0.8X mix" as it's more descriptive. I mean, if I know that 1X = 1 ATM, then 0.8X is 0.8 ATM. Easy enough. But if I go with the "ambient" definition, then if somebody tells me they did a 1X mix in Denver.... Well, unless I break out my atmospheric tables I have no friggin clue what that really means!

I guess I'll continue forward unless somebody has some compelling argument for the "ambient" scenario.

Short version: I expect to have a "GGDT-like" tool for hybrids ready for beta testing within a few weeks. I know it's not the first hybrid predictor, but hopefully it'll be the most informative.
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Unread postAuthor: TurboSuper » Thu Mar 20, 2008 3:11 pm

1X=Ratio of propane to oxygen present in the air;
2X=Twice the propane with twice the oxygen that air has.

...and so on

I always thought the "nX" system was just a simple way of comparing stochiometric ratios of oxygen to propane. Using Atm seems like just a simple way of having a nice, round number to work with.

But hey, whadda I know about hybrids :?
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Unread postAuthor: Brian the brain » Thu Mar 20, 2008 3:31 pm

Did you READ BEFORE YOU ANSWER?

I doubt it.

He wasn't really asking what it means, he wants you to think about it.
Is, what we mean by 1x,2x actually right, or do we assume things based on a wrong idea.
D-hall knows his stuff.
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Unread postAuthor: BC Pneumatics » Thu Mar 20, 2008 3:32 pm

My explanation was poorly written...

I was trying to point out the two ways of looking at the "x system"
First would be 1X=1ATM ("To make a 5x mix, I must pressurize to 5ATM")
Second is 1X=1(Atmospheric Pressure) ("To make a 5x mix, I must pressurize to 5(Atmospheric Pressure)")

I do not know if anyone in the beginning said that our Nx system was based off the ATM unit (14.7psi etc) or off the atmospheric pressure (being defined as "The pressure exerted by the atmosphere at a given point.") - the ambient pressure in relation to the launcher.

I agree that of the two, 1X=1ATM is the better way of going about things, but was just pointing out that others may see things differently.

So I know this sounds very simple and I kind of like the sound of the "x factor" but why don't we take a few minutes to do the math and figure out what PSI the fuel and air mix is?


Using the first method, what you are suggesting is exactly what we are doing, expressing the fuel/air mix total pressure. Since 1X=1ATM, 1ATM=1.01Bar, 1.01Bar=14.5psi, then a 5X mix=5ATM=5Bar=72psi

It is just unfortunate that you grew up in the wrong country for convenient hybrid calculations. While we have to convert these mixes to psi equivalents, it is one of the few things around here that everyone besides the US doesn't have to convert. (Other than the simple ATM to Bar conversion, which can be considered 1:1 in most situations)


On a personal note, I have always liked the idea of measuring the fuel contained in a combustion mix by the weight of the propane used. Of course if something like hydrogen, mapp, etc. was used, you would have to convert it in to the propane equivalent.
You could have a "419mg Cannon" in much the same way as you could have a "3Megaton Bomb".
Hell, if we all like scientific notation, we could just measure in actual TNT equivalent megatons...
This system would also work for non hybrid combustions, being a direct reflection of chamber volume (and atmospheric pressure)
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Unread postAuthor: Hotwired » Thu Mar 20, 2008 5:30 pm

I don't believe anyone actually does mixes according to their local atmospheric pressure.

Multiples of 1atm (being 14.7psi) perhaps rounded to a more comfortable 15psi is what generally happens.

But nevertheless the ambient pressure still affects those readings because if at 12.3psi atmospheric pressure a 15psig mix is made thats still a weaker mix than the same thing done at 14.7psi atmospheric pressure as less molecules will be present in the chamber.

Short of everyone getting down to sea level to fire hybrids theres not much that can be simply done about it without fiddling with calculations to get the same moles of air/propane in there.

Interesting insight thread.
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