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Query on kerosene and LPG

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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Query on kerosene and LPG

Unread postAuthor: FiveseveN » Sat Aug 04, 2007 3:39 pm

In the old days I used to make small flamethrowers from bug spray cans. Recently it has come to my attention that I could use them as fuel for a combustion or hybrid cannon.
Killtox is 50% Kerosene and 49% LPG (Propane - Butane) and is in fact a lot cheaper and more commonly available than the butane cans I've used so far.

The calorific value of LPG is 94 MJ/m³ ; kerosene's is 40-something. That's lower than butane's 133 MJ/m³, but the cost/energy ratio would still be in Killtox's favour.

Haven't tested it in a cannon yet since I don't have a complete one at the moment; just wanted to hear what you guys think. Hopefully I'll make a small metal hybrid soon and I want to see if I could use this as fuel.
Also, I have the option of my old electronic ignitor vs. camera flash (I could add more caps, maybe an ignition coil). Which one do you figure would be more suitable for a hybrid using either kerosene+LPG or butane?
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Unread postAuthor: DYI » Sat Aug 04, 2007 4:24 pm

To use this in a hybrid you would have to know the exact percentages of each component in the fuel, and use this to calculate what a stoichiometric mixture with air would be.

As far as fuels go, the differences between butane, LPG, and propane in terms of power provided are not noticeable in a normal combustion.

In the kerosene+LPG vs. butane debate I would choose butane, as hybrids aren't exactly cheap to begin with. However, MAPP gas is a better fuel than either of these choices.
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Unread postAuthor: FiveseveN » Sun Aug 05, 2007 3:23 pm

Since it's a small chamber (around a liter, I guess), I don't think complex calculations will be of any use, since the control system to inject a precise amount of fuel is beyond my scope.
I still have some butane and plenty of Killtox, so I guess the best course of action is to just build the cannon, test different scenarios and judge for myself.
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Unread postAuthor: DYI » Sun Aug 12, 2007 5:53 pm

Well, I can guarantee that if you don't meter the fuel precisely, your hybrid won't work. Using aerosol fuels isn't really possible on a proper hybrid.
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Unread postAuthor: frankrede » Sun Aug 12, 2007 6:07 pm

Its possible. Just not practical.
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Re: Query on kerosene and LPG

Unread postAuthor: jimmy101 » Mon Aug 13, 2007 4:03 pm

FiveseveN wrote:The calorific value of LPG is 94 MJ/m³ ; kerosene's is 40-something. That's lower than butane's 133 MJ/m³, but the cost/energy ratio would still be in Killtox's favour.


You can't compare two fuels based on their calorific content or their heats of combustion. Different fuels will require different amounts in a fixed size chamber. The limiting quantity is the amount of oxygen in the chamber. The quantity of fuel that should be used is then calculated to match the amount of available oxygen using the balanced chemical equation for combustion of the fuel.

If you can find a reasonably accurate description of what kerosene is, and the actual percentages of propane and butane in LPG, then you can calculate the amount of fuel needed for a particular chamber size. I think you'll find that all of these fuels have very nearly the same energy content (+/- a couple percent) per volume of oxygen available.
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