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Can someone check these metering calculations?

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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Can someone check these metering calculations?

Unread postAuthor: Dave_424 » Wed Jun 24, 2009 10:25 am

Hey guys, just wondering if someone could check over these calculations for manometric metering

Volume of the chamber = 19.6349541 * 28 = 549.778715 cm cubed
549.778715 cm cubed in inches cubed = 33.5495556 inches cubed
Calculation for 10X mix
(33.5495556 * 10)/0.958-(33.549556 * 10) = 14.7085694 inches cubed of propane
By how much has the chamber pressure risen?
14.7085694/33.5495556 = 0.438413241
0.438413241 * 14.7 = 6.44467464 psi for 10X mix
Add 9 atmospheres of air and fire


Also, is there an easier way to get the results of the amount of psi of propane I have to add from 1 - 15X mix?

Thanks Guys

Dave
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Unread postAuthor: THUNDERLORD » Wed Jun 24, 2009 10:56 am

Looks interesting to study.
I have no time right now :( Got a side job fixing a completely broke toilet and plumbing...No plumbing experience besides spudding but I'm feelin' confident... :lol: :D 8)
BTW, (It's not poopy or anything, just a bunch of messed up internals and valve).
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Unread postAuthor: Dave_424 » Wed Jun 24, 2009 10:59 am

HAHA okay go and tend to your toilet

thanks for giving a reply anyway

Dave
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Unread postAuthor: daccel » Wed Jun 24, 2009 3:14 pm

In HGDT, go to Tools > Load/Mix Calculator, and enter your specs.

I probably wouldn't be playing with hybrids without that. Not that I'm lazy, just mathematically challenged :D
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Unread postAuthor: Dave_424 » Wed Jun 24, 2009 4:12 pm

I have HGDT but didn't know it had that facility

Dave

EDIT: as far as can see, HGDT cannot calculate the manometric metering method that I am using

Can anyone confirm my numbers?
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Unread postAuthor: ramses » Wed Jun 24, 2009 6:33 pm

I think the HGDT metering tool is flawed. I multiply mix by .61 to get propane pressure in psi.

For air, either of these work:

* psi= ((mix#-1)*14.7)+propane pressure
* psi= ((mix#-1)*14.7)+ (mix#*.61)

EDIT:

for 10x mix, I see 10*.61= 6.1psi propane followed by (14.7*9)+6.1= 138.4 psi air.


for an explanation of the .61 psi number, assume a 100cu in chamber.

the ideal mix is 4.2% of propane, so 100* .042= 4.2cu in propane

add this to the 100 cu in of air, and get 104.2.

divide this by 100 to get 1.042, which is in bar. (absolute). subtract the 1 to get relative pressure since atmosphere is nearly 1 bar, and convert .042 bar into psi to get .61 psi/x

the absolutely correct answer is 0.609158498 psi/x but .61 is close enough.
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Unread postAuthor: Dave_424 » Wed Jun 24, 2009 7:24 pm

Okay, I seem to be pretty bad with these kind of calculation and just want to be clear about it

Could you check the number Psi of propane added to the chamber?

The chamber is 33.5495556 cubic inches

for 15x mix i get 9.66701196 psi of propane

and 5x mix i get 3.22233732 psi of propane

can someone check their results so i can confirm that the rest of my numbers are correct

Dave
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Unread postAuthor: mark.f » Wed Jun 24, 2009 8:24 pm

Not to be self-promotional or anything, but I did a write-up a few days ago at http://www.spudstalker.net/hyfuel.html on hybrid fueling. It should answer your question about how much the propane affects final pressure, and what the final mixture pressure should be for x mix.
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Unread postAuthor: Dave_424 » Wed Jun 24, 2009 8:37 pm

Thanks for that Mark

That really helped, Im now confident that my numbers are correct.

Now to order the parts and start assembling

Dave
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