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gas or hairspray

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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hairspray or propane/gas

Poll ended at Mon Oct 08, 2007 3:29 pm

hairspray
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propane/gas
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Total votes : 8
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gas or hairspray

Unread postAuthor: WEEMAN » Mon Oct 01, 2007 3:29 pm

what acellerant would work for a smaller combustion gun(small being about
5feetlong x 5inches wide)hairspray or propane
and.......
i want to know if anybody here has actually made a gas powered spud gun!!!!!!!!
pictures PLEASE
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Unread postAuthor: Pete Zaria » Mon Oct 01, 2007 3:38 pm

Dude, do you really need to ask? 90% of the combustion guns on this forum use propane.

The "advanced combustion guns" have propane meters (built from brass plumbing fittings, ball valves, and gauges) that meter out an exact amount of propane to give the correct fuel:air mixture every time. We also use fans in the chamber to mix the gases together and to vent out the chamber between shots. Other marks of an "advanced combustion" are breech loading, ball valves to vent out the chamber, multiple spark gaps, and a beefed-up ignition system. Check out the Cannon Showcase for some examples.

The answer to your question is overwhelmingly "propane", and you need to READ THE WIKI, because it explains all of this in detail.
Additionally, this question has been asked 500+ times before... Search first.

Edit: Did you mean gasoline, not propane gas? There have been gasoline-powered guns posted here before (should NOT be attempted with plastic pipe).

I was going to lock this thread, but I'll leave it alone for awhile...

Peace,
Pete Zaria.
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Unread postAuthor: Fnord » Mon Oct 01, 2007 4:35 pm

Thanks for not locking this, cause I have a related question to ask:

Is there any type of calculator or formula I can use to figure out how much gasoline I should use for a given chamber volume?
In this case I would need to find what would be optimum for a 1250 CI chamber.
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Unread postAuthor: f.c » Mon Oct 01, 2007 6:02 pm

i dont think you can really ov er fuel using gasoline. try a tablespoon for an averaged sized combustion.
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Unread postAuthor: benstern » Mon Oct 01, 2007 11:28 pm

Dude it is extremely easy to overload with gas you need 5 drops max!....noob
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Unread postAuthor: Redcoat » Mon Oct 01, 2007 11:31 pm

Woah, woah. What's with the sudden flaming thee benstern?

And I'd Go propane.
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Unread postAuthor: spudgunnerwryyyyy » Mon Oct 01, 2007 11:48 pm

I would say use denatured alcohol. It is volatile so you won't have to wait long and it burns the cleanest out of any fuel. Slightly more powerful than propane, think .5 of a percent. Good luck!
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Unread postAuthor: SpudBlaster15 » Tue Oct 02, 2007 12:22 am

_Fnord wrote:Thanks for not locking this, cause I have a related question to ask:

Is there any type of calculator or formula I can use to figure out how much gasoline I should use for a given chamber volume?
In this case I would need to find what would be optimum for a 1250 CI chamber.


Well, its actually quite simple.

The stoichiometric ratio of Air:Octane is 98.32:1.68. This means that you require 20,483.9*0.0168 = 344.130ml of gaseous octane in the chamber. At room temperature, 1 mol of any gas occupies 24 liters of volume. You will thus have 344.130/24000 = 0.014 moles of Octane in the chamber. Gaseous octane has a molar mass of ~114.229 grams per mol. Your chamber will contain 114.229*0.014 = 1.6 grams of octane. Liquid octane has a density of 0.703g/ml. 1.6/0.703 = 2.276ml of liquid octane.

The more accurate way is to combine it all into a single equation.

Volume of Liquid octane = (((Chamber volume in ml*0.0168)/24000)*114.229)/0.703

Edit: F*cked up my place values.
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Last edited by SpudBlaster15 on Tue Oct 02, 2007 12:33 am, edited 2 times in total.
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Unread postAuthor: benstern » Tue Oct 02, 2007 12:26 am

Thing is....gasoline is not a single compound. It is a mixture of many compounds, much like air.
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Unread postAuthor: SpudBlaster15 » Tue Oct 02, 2007 12:32 am

Gasoline is primarily Octane, and such the approximation I proposed is accurate enough to determine a baseline estimate as to how much gasoline should be added to the chamber.
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Unread postAuthor: jimmy101 » Tue Oct 02, 2007 10:42 am

Pete Zaria wrote:Edit: Did you mean gasoline, not propane gas? There have been gasoline-powered guns posted here before (should NOT be attempted with plastic pipe).

PVC should't have any problem when fueled with the proper amount of gasoline. For most sized guns, the stoichiometric amount of gasoline is only a few drops.

Various source with info on the chemical resistance of PVC disagree on gasoline:
http://k-mac-plastics.com/data%20sheets ... stance.htm says non-rated.
http://www.vp-scientific.com/Chemical_R ... _Chart.htm says PVC has good resistance to gasoline.
http://www.omega.com/pdf/tubing/technic ... hart_2.asp says "moderate" affect but not "Not Recommended".

I would say that making a gasoline storage tank out of PVC is probably not a good idea. Using a few drops in a standard combustion gun should not be a problem.
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Unread postAuthor: spud yeti » Tue Oct 02, 2007 10:48 am

propane, definitely
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Unread postAuthor: spudgunnerwryyyyy » Tue Oct 02, 2007 1:57 pm

Ok still no one said ethanol. It doesn't have any affect on PVC and its very clean burning. Plus its easy to use with larger chamber. You can also use more fuel than with Octane.
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Unread postAuthor: frankrede » Tue Oct 02, 2007 7:19 pm

a small combustion?
That is 5 ft long, 5 in wide?
Something doesn't sound right.
Either this guy is extremely new to spud guns or is an idiot
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Unread postAuthor: jimmy101 » Wed Oct 03, 2007 10:23 am

spudgunnerwryyyyy wrote:Ok still no one said ethanol. It doesn't have any affect on PVC and its very clean burning. Plus its easy to use with larger chamber. You can also use more fuel than with Octane.

Yes, ethanol will work but it really doesn't have much advantage over any other fuel, and it has some disadvantages.

It is not easy to get. If you are younger than 21 you probably can't get it at all. You would really like 200 proof ethanol with or without denaturant. The denaturant is usually methanol or benzene and is present to make the ethanol poisonous. If the ethanol is dantured then you don't have to pay the $20/gallon (IIRC) tax and a gallon will only cost a buck or two.

Ethanol will not burn cleaner than other pure fuels like propane, butane, gasoline etc.

"You can also use more fuel than with Octane" this is technically correct but totally irrelevant. The proper amount of fuel is limited by the amount of air in the chamber and the combustion stoichiometry. You'll find that with most simple hydrocarbons and alcohols that though the amount of fuel used varies the total energy available from combustion is essentially the same. Comparing ethanol to propane you'll find that the ethanol provides just 4% more energy than propane. It is unlikely that you could measure the difference in performance of a gun caused by increasing the available energy by 4%.

Gasous Fuels like propane:
SpudWiki
Another Site

Liquid Fuels like gasoline:
here
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