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Liquid Fuel

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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Liquid Fuel

Unread postAuthor: meatballs » Fri Apr 27, 2007 11:08 pm

I have lately been contemplating the idea of using a volatile liquid as the fuel for my cannon. I want something that i can measure as a liquid but that will evaporate in the cannon. I have thought of alcohol, probably ethanol (5% propanol so you can't drink it) because i have access to that. Does anyone have any experience with this? any sort of ratio for liquid volume to chamber volume? do you think i'd be off with methanol, ethanol, or propanol, or some other non alcohol liquid?
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Unread postAuthor: homedepotpro » Fri Apr 27, 2007 11:45 pm

ive used gasoline but i put in a spray bottle, tey don't always burn completely, so you have to be careful
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Unread postAuthor: Pyro Ninja » Sat Apr 28, 2007 2:19 am

Some of the liquids might start to dissolve the pvc...maybe... :?
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 28, 2007 2:40 am

There was someone on here who was using heptane as fuel.

http://www.spudfiles.com/forums/im-stil ... t7285.html
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Unread postAuthor: lukemc » Sat Apr 28, 2007 6:16 am

heptanes liquid? didnt know i have an aerosle can that heptanes the first ingredient and man does that work
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 28, 2007 6:38 am

At room tempterature, yes
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Unread postAuthor: meatballs » Sat Apr 28, 2007 2:32 pm

how would one go about accuiring heptane? would it have any negative effects on the pvc? How fast does it evaporate?
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Unread postAuthor: Hotwired » Sat Apr 28, 2007 2:53 pm

Why do you need to measure the fuel as a liquid?

You'd also need to atomise the fuel using a spray and/or wait for it to evaporate much like a hairspray setup...

*Edit: actually it could greatly reduce the clutter of a gas measuring setup depending on how you planned on getting the liquid into the chamber.
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Last edited by Hotwired on Sat Apr 28, 2007 2:59 pm, edited 2 times in total.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 28, 2007 2:55 pm

meatballs wrote:how would one go about accuiring heptane? would it have any negative effects on the pvc? How fast does it evaporate?


It's highly volatile. We use it as a solvent at work so we get it in 45 gallon drums, as far as I can tell it doesn't attack PVC. I suppose you could get it from a laboratory chemical supplier, but it will probably cost a little.
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Unread postAuthor: BC Pneumatics » Sat Apr 28, 2007 5:42 pm

May I suggest... propane? Getting it to the meter in a liquid form wouldn't be all that difficult, and once it is in the chamber, it will change phase to a gas.

denatured alcohol, as you mentioned earlier would work, but be careful when using new fuels. Thats a lotta' energy to be toyin' with.
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Unread postAuthor: meatballs » Sun Apr 29, 2007 8:27 pm

yeah, alcohol has a lot of power. i put .4 ml in a gatorade bottle and let it evaporate, and it made quite the boom when ignited. scale that up to a full size chamber and it would be quite powerful.

and yes i'm going with propane (metered as a gas, not the liquid) but i think it would be cool to make a cheap easy metering system and a liquid lends itself nicely to that purpose since it doesn't require all the valves, pressure gauges, regulators, etc that propane needs. just a syringe and you're all set.
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Unread postAuthor: mark.f » Mon Apr 30, 2007 6:30 am

I've been using 91% isopropyl alcohol for a while now in my BS combustion. I just measure out a few CC's, (6), close off the chamber, shake it up, and then heat it up with a blowdryer or just wait a few minutes while the alcohol evaporates. Shoots very nice.
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Unread postAuthor: jimmy101 » Mon Apr 30, 2007 11:27 am

The only way to accurately measure the small volume of liquid would be with a syringe. (Get'm for cheap from your local farm supply store).

Lets see, assuming a 100in<sup>3</sup> chamber, hexane as fuel;
2C<sub>6</sub>H<sub>14</sub> + 19O<sub>2 </sub>= 12CO<sub>2</sub> + 14H<sub>2</sub>O
So you need 2/19 volumes of gaseous hexane for every volume of Oxygen. But air is only ~20% oxygen, so you need (2/19)*0.2 volumes of gaseous hexane for each unit of chamber volume.

100in<sup>3</sup>(2/19)*0.2= 2.5% by volume of gaseous fuel.

Density of hexane at NTP = 0.66g/ml
Molecular weight of hexane = 86g/mol
100in<sup>3</sup> = 1.64Liters
2.5% of 1.64L is 0.041L
(0.041L)(mol/22.4L)(86g/mol)(ml/0.66g) = 0.24 ml of liquid hexane

A "generic" drop of liquid is about 0.06ml, so, about 4 drops of hexane is needed for a 100in<sup>3</sup> chamber.

To use a syringe it would have to be a pretty small one, say 1ml total volume.

The boiling pont of hexane is 69C (156F) but the heat of vaporization is pretty low so a chamber fan should vaporize a small amount of hexane fairly quickly.

I make no gaurantees that I didn't hose my math somwhere.
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Unread postAuthor: Abigor » Mon Apr 30, 2007 11:39 am

stick with gas, too much pissing about when you try and use fuel
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Unread postAuthor: meatballs » Mon Apr 30, 2007 2:12 pm

yeh, i think i will just go with propane. i just got the stuff for my meter and am assembling it. should be awesome, it'll be regulated for easy operation and is detatchable via quick disconnect so i can use it on multiple cannons.
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