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Fuel Type?

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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Unread postAuthor: zagnut » Tue Jan 29, 2008 10:31 pm

While I'm no chem major, gasoline is actually quite explosive when vaporized. If you care to visit, I'll take you across the road a quarter mile away where a small family diner used to be. A disgruntled employee attempted to burn it down. Well, the gasoline vapors accumulated a little much before setting fire. I thought a plane crashed in my back yard and the police found him about a mile away walking in a daze, burnt to a crisp, not knowing where he was or who he was. I personally, would rather take my chances with hydrogen.

BTW, another way hydrogen can be obtained involves aluminum and a certain acid readily available at your local hardware store. As pointed out above with electrolysis, this is a rather slow process as well.
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Unread postAuthor: daberno123 » Tue Jan 29, 2008 10:43 pm

There is all this talk about H2/O2 mixes in hybrids but has anyone actually used it in a hybrid?
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Unread postAuthor: jimmy101 » Wed Jan 30, 2008 11:22 am

zagnut wrote:While I'm no chem major, gasoline is actually quite explosive when vaporized.

So you think propane in air isn't explosive? Or that a natural gas (propane) leak in a building can't cause the same magnitude of damage as an idiot with a gallon of gas?
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Unread postAuthor: psycix » Wed Jan 30, 2008 3:37 pm

jimmy101 wrote:Nope, H<sub>2</sub> is not way more powerful than propane. But it does burn much faster and is apparently much more likely to reach DDT than propane. The burn speed and DDT probability is why it is usually considered unsafe, not the difference in potential energy.


Yes, I know it isnt in the energy, but in the burn speed, wich causes a schockwave, wich blows your chamber.
Question:
How safe is it to use H<sub>2</sub> /O<sub>2</sub> (or maybe just H<sub>2</sub>/air) in a normal combustion? (PVC!)


Another thing I have to add:
Fuels that burn faster can be considered more powerful since the pressure buildup is faster. (While having the same amount of energy/mol)
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Unread postAuthor: rcman50166 » Wed Jan 30, 2008 8:16 pm

Well I think it would have to be the expanison ratio that draws the most power. The format of the potato gun can be determined by the rate at which a fuel expands (i.e. a longer burn requires a longer barrel with a larger chamber to barrel ratio, the opposite goes for a shorter burn.


A bit off topic but how is everyone getting the subscript letters. I've had to us the unprofessional looking H2/O2 format. :oops:
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Unread postAuthor: Lentamentalisk » Wed Jan 30, 2008 9:37 pm

Code: Select all
H<sub>2</sub>.


that shows up as:

H<sub>2</sub>
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Unread postAuthor: jimmy101 » Thu Jan 31, 2008 11:45 am

psycix wrote:
jimmy101 wrote:Nope, H<sub>2</sub> is not way more powerful than propane. But it does burn much faster and is apparently much more likely to reach DDT than propane. The burn speed and DDT probability is why it is usually considered unsafe, not the difference in potential energy.


Yes, I know it isnt in the energy, but in the burn speed, wich causes a schockwave, wich blows your chamber.
Question:
How safe is it to use H<sub>2</sub> /O<sub>2</sub> (or maybe just H<sub>2</sub>/air) in a normal combustion? (PVC!)


Another thing I have to add:
Fuels that burn faster can be considered more powerful since the pressure buildup is faster. (While having the same amount of energy/mol)

Good point, especially when the burn rate goes up significantly like it does with H<sub>2</sub> compared to propane.

I wouldn't recommend making a PVC gun that uses H<sub>2</sub> and air. H<sub>2</sub> burns too fast and may produce too much shock load on the PVC. H<sub>2</sub> + O<sub>2</sub> would not only burn even faster, and create ~5X as much energy in the chamber as air, it may also reach DDT.
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Unread postAuthor: VirusX » Tue Oct 06, 2009 9:20 am

Deodorant:

good:

-cheap
-easy to get
-good metering because of the nozzle
-has a reasonably power


bad:

-after a few shots your champer gets wet, sticky and slushy
-attacks screws and other things out of metal (---> rust)
-it sticks at the ignition cable, you have to clean it after a few shots
-The more shots I made, the more ignition problems did I get because of the wet and sticky champer

I don't recommend deodorant, there are much better fuels for cc's.

Edit: Oh I see the topic is old :(
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Unread postAuthor: rcman50166 » Tue Oct 06, 2009 9:45 am

It's fine to kick up old topics as long as something useful is contributed the discussion. You're addition qualifies for such.

And since I already have posted. I may as well post something on the topic. I have added aerosol deodorants to the bad list because of all the non-flammable additives. It makes the chamber nasty and will eventually coat you igniter with a residue that prevent a jump.

Also I wrote they were actually hard to meter because although you can get a final volume by taking the volumetric flow rate of the nozzle and multiplying it by time. The trouble with that is the flow rate isn't know until some testing is done. Also it isn't really worth it until the timing can be accurate enough. This means, with human error, the best you can do with timing will prevent you from getting the best fuel mixture possible.
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Unread postAuthor: john bunsenburner » Tue Oct 06, 2009 11:22 am

You left out the following(i can't give info on them):

-Zippo
-ethonol
-methonol
-diesel
-Kerosene

I am sure there are more but those are major ones.
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Unread postAuthor: rcman50166 » Tue Oct 06, 2009 11:28 am

Well if you can find someone who has used the fuel in a cannon I can post it. But not until then. I personally have no experience with these fuels
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Unread postAuthor: john bunsenburner » Tue Oct 06, 2009 11:48 am

"Ethanol belongs to the group of hydrocarbons known as alcohols. The density of ethanol is approximately 790 grams per liter this means it is a liquid. The chemical formula for ethanol is CH3CH2OH. Its structure appears like this

H H
| |
H-C-C-O-H
| |
H H

When combusted, ethanol forms water and carbon dioxide as follows:
CH3CH2OH + 3O2 -> 3H2O + 2CO2






A liquid fuel can be desirable as an alternative to pressurized gas fuels because of the lower risk or accidental detonation. The high heat resulting from burning alcohol’s has been know to set fire to the spud gun’s firing chamber."
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Unread postAuthor: jimmy101 » Wed Oct 07, 2009 12:52 pm

john bunsenburner wrote:The density of ethanol is approximately 790 grams per liter this means it is a liquid.

no it doesn't. Some woods have densities of 790g/L.

A liquid fuel can be desirable as an alternative to pressurized gas fuels because of the lower risk or accidental detonation.

not really. A liter of ethanol has roughly the same chemical potential energy as does a Bernzomatic cylinder.

The high heat resulting from burning alcohol’s has been know to set fire to the spud gun’s firing chamber.

not really. It is very easy to over fuel with a liquid. It's the excess liquid that continues to burn after firing. That might set the PVC aflame but that's not because of the "high heat", it's because of too much fuel.
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Unread postAuthor: Heimo » Sun Oct 25, 2009 3:31 pm

Hi new to this forum. Anyhow I have been playing with spud guns for quite a while now. (I will post a proper intro tomorrow) OK I use methylated spirits as fuel for my combustion spud gun and I have very good results I must add that my spud gun has a steel chamber so I do not know how this fuel will react in a PVC spud gun
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Unread postAuthor: niglch » Mon Oct 26, 2009 12:39 am

Has anyone ever tried using methane (CH<sub>4</sub>)? I would venture to guess that it would be somewhat superior to propane due to chemical structure (all C-H bonds).
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