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Percent by volume for fuel air mixes

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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Percent by volume for fuel air mixes

Unread postAuthor: Secret Squirrel » Fri Mar 18, 2011 3:44 pm

I'm working on a little project, that once finished could be helpful to those of you working on hybrids or advanced combustions.

I've gotten everything I need other than the percentages for a combustible mix (at atmospheric pressure) of Butane, and the same for MAPP. Also, am I correct that the mix for propane is 4.2%?

Thank you for helping us help you help us all...
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Unread postAuthor: Fnord » Fri Mar 18, 2011 4:39 pm

http://www.spudfiles.com/spud_wiki/inde ... tle=Butane

http://www.spudfiles.com/spud_wiki/index.php?title=Mapp

3.2% and 4.6% respectively.

Also, it's 4.2% assuming you don't leak that small volume of air when the propane is added. If you do it's closer to 4%.
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Unread postAuthor: Secret Squirrel » Fri Mar 18, 2011 4:51 pm

Thanks

I'm working a simple fueling calculator based off of SpudBlaster15's hybrid fueling 101 thread. I just needed those values as constants for the program.
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Unread postAuthor: jimmy101 » Fri Mar 18, 2011 6:10 pm

Besides the fuel-specific pages Fnord linked there is;
http://www.spudfiles.com/spud_wiki/inde ... n_Spudguns
scroll down to the first table.
Edit: The table also gives values for both "additive" (no air is displace by the fuel) and "displacive" (a volume of air equal to the volume of the fuel is displaced from the chamber)" fueling.
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Unread postAuthor: Secret Squirrel » Fri Mar 18, 2011 8:48 pm

Well the programming is finished. In its current form it can calculate fueling measurements for traditional meters, chamber (manometric) meters, and syringe (volumetric) meters for propane, butane, and MAPP. It's still going to undergo a little further testing and tweaking, but could be ready soon, if I can figure out how to convert .py to .exe.

Edit: Anyone willing to submit mixes they've successfully used in their hybrids so I can confirm the program's results?

For traditional style meters I would need your fuel, mix #, chamber volume, and meter volume, along with your meter pressure to check my result.

For syringe meters I would need your fuel, mix, and chamber volume, along with the volume of fuel used.

And for manometric meters I would need your fuel and mix along with the increase in chamber pressure during fueling.

I would just like to know that the results are accurate to real hybrids.
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Unread postAuthor: Technician1002 » Sat Mar 19, 2011 8:54 am

And for manometric meters I would need your fuel and mix along with the increase in chamber pressure during fueling.


Use Boyle's gas laws and work in Absolute pressure instead of Gauge pressure. This will vary depending on local atmospheric pressure and temperature if you use relative pressure instead of Absolute.
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Unread postAuthor: saefroch » Sat Mar 19, 2011 9:19 am

Here is an already working hybrid spreadsheet.
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Unread postAuthor: Secret Squirrel » Sat Mar 19, 2011 11:30 pm

saefroch wrote:Here is an already working hybrid spreadsheet.


I see...

Well there's a few hours wasted. At least it was good practice for my Computer Science exam Monday.
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Unread postAuthor: saefroch » Sun Mar 20, 2011 12:43 pm

No time spent programming is wasted!
:D
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Unread postAuthor: jimmy101 » Sun Mar 20, 2011 12:57 pm

Secret Squirrel wrote:Well there's a few hours wasted. At least it was good practice for my Computer Science exam Monday.

Not at all. What Saefroch said, and by writing the code you made sure you actually understood the math, chemistry and physics.

Plus, there is always a chance that the existing codes are wrong.

(edit for engrish)
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Unread postAuthor: saefroch » Sun Mar 20, 2011 1:01 pm

Existing codes ARE wrong... my calculation for max fueling error went wacky when I added in the input for atmospheric pressure and the column for syringe metering. I'd appreciate a correction if you come up with one :wink:.
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Unread postAuthor: Hotwired » Sun Mar 20, 2011 1:35 pm

saefroch wrote:No time spent programming is wasted!
:D


I recall much time spent debugging code I'd failed to comment when I wrote it years ago.


Suppose it wasn't totally wasted, I now write almost as much in comments as code sometimes. Lesson learned :P
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Unread postAuthor: Secret Squirrel » Sun Mar 20, 2011 5:30 pm

I actually spent more time figuring out how to program a GUI for this than anything, and so the actual calculations are a little simplified. Atmospheric pressure was listed as a constant 14.7psi, and I feel like there's still a bug when calculating syringe metering, but all of that should be easily fixed.

I'd also like to add in a unit converter so it also works in metric units, and more fuel options wouldn't hurt.

And I definitely need to add some more comments.
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