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midsized Combustion Fueling

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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midsized Combustion Fueling

Unread postAuthor: Lockednloaded » Fri Nov 06, 2009 6:00 pm

Combustions can be fueled by many things, but with out a metering system consistency is hard. I dont have the money for propane metering system, so i came up with a new idea for fueling with alcohol (not booze, more along the lines of ear drops and such) or any other liquid fuel. My idea is to soak a cotton ball in the liquid then place it in the cannon, the fumes would ignite, hopefully not the cotton ball, and the shot would fire. I could have pre soaked cotton balls and i could fire with pretty consistent results. I have not tested, but do you think this would be a viable way to fuel a combustion?
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Unread postAuthor: kjjohn » Fri Nov 06, 2009 7:59 pm

The cotton balls could be sort of like cartridges, but you would need to make sure that the spark actually intersected the cotton ball for best results.
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Unread postAuthor: Lockednloaded » Fri Nov 06, 2009 11:51 pm

yea, cartridge is the idea, but are you sure the spark needs to goe through tthe cotton ball, because i thought that the fumes were combustable
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Unread postAuthor: starman » Sat Nov 07, 2009 1:06 am

A reasonable propane metering system can be implemented in the $30-40 range. do you consider that too expensive? Can be used on multple cannon projects....

Why do you think a random cotton ball would would properly "fume" any particular sized chamber? Why do you believe it wouldn't catch on fire?
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Unread postAuthor: theBOOM » Sat Nov 07, 2009 2:27 am

Hm a very ghetto yet working idea is one created by this old member.. just search on completed cannons "automatic combustion gun" or something similar.... I remember it used some kind of liquid fuel and a constant spark.
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Unread postAuthor: Lentamentalisk » Sat Nov 07, 2009 2:41 am

If you can't afford a real metering system, you can always go for a rough metering system by opening a needle valve for a specific amount of time. Just experiment with different times, until you find the lower and upper combustibility limit, and shoot for something in the middle.
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Unread postAuthor: CpTn_lAw » Sat Nov 07, 2009 4:22 am

Or you could use you brain and find another way out, calculate de volume of pure propane you need inside the chamber (4.2% total chamber volume) , buy a small propane torch (10$), buy a syringe (without the needle 1$) and simply inject propane from the syringe into the chamber until you get the desired amount.
Chamber-fan could be used to mix the gaz and ensure proper "consistency" if that's what you're about.
hope this helps
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Unread postAuthor: Lockednloaded » Sat Nov 07, 2009 12:10 pm

yea, but the price is not the only thing keeping me from propane metering, my parents don't like the idea of propane they think it is too "dangerous," despite the fact i have two pneumatics that i take over 120psi.
@starman: I don't think the cotton ball would catch on fire because im pretty sure the fumes are he combustable thing, and even if the ball does catch on fire, it can't do much harm, but correct me if i'm wrong.
@theBOOM: yes have seen that gun, and it gave me this very idea.
@CpTn_lAw: I have a chamber fan, and it works well, but i just don't like using aerosols, I have read many forums which say they are the worst fuel, and anyway i don't like their stick residue.
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Unread postAuthor: starman » Sat Nov 07, 2009 12:28 pm

Lockednloaded wrote:@starman: I don't think the cotton ball would catch on fire because im pretty sure the fumes are he combustable thing, and even if the ball does catch on fire, it can't do much harm, but correct me if i'm wrong.


The cotton ball would more likely catch on fire when you reopen the chamber allowing air back in. You don't want anything catching on fire...ever. Trust me, the cotton ball concept is a non-starter.

If your parents are of the sort to disallow propane for whatever wrongly or rightly imagined reason, then maybe you should stick with pnuematic models.
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Unread postAuthor: jimmy101 » Sun Nov 08, 2009 11:15 am

The cotton ball has lots of problems besides catching on fire (which it will).

The amount of liquid fuel required for a typical size gun is miniscule. Usually in the range of a couple drops. So you are grossly overfueling the chamber with a soaked cotton ball and have defeated the attempt at metering.

You might want to read up on using liquid fuels in spud guns.

Careful use of an eye dropper may be accurate enough with a higher boling fuels like ispropanol (rubbing alcohol). Eye droppers work very poorly with low boiling liquids like methanol.

You will need a chamber fan to get the fuel to fully evaporate.
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Unread postAuthor: grock » Sun Nov 08, 2009 4:37 pm

Lockednloaded wrote: I have read many forums which say they are the worst fuel, and anyway i don't like their stick residue.


actually, if you use static guard, you get fairly good performance, with little to no residue
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Unread postAuthor: jimmy101 » Sun Nov 08, 2009 6:15 pm

grock wrote:
Lockednloaded wrote: I have read many forums which say they are the worst fuel, and anyway i don't like their stick residue.


actually, if you use static guard, you get fairly good performance, with little to no residue

Or starter fluid. If the can contains nothing but flammable propellant and flammable fuel then there is no residue.

Anything designed to be squirted into the carburetor of a gasoline engine is not going to be leaving any residue behind.

Any spray is gong to be difficult, if not impossible, to get consistent.
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