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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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Fuel Type?

Unread postAuthor: rcman50166 » Sat Jan 26, 2008 12:19 pm

What is the best fuel type to use in a combusiton cannon. By asking this question I want to make a master list for this site for all members to use. The fuel you submit doesn't have to be the best. I just want feedback on fuels you've tried even if they don't work. I wan't to know why they are good/bad fuels.

Please feel free to disagree with the list I make.

To start the list

Good

Propane It is cheap, powerful, clean, and plentiful
Vaporized gasoline It is relatively cheap, powerful, and currently plentiful
MAPP gas More powerful than propane, cheap, clean, and plentiful
Hydrogen powerful and clean most energetic chemical/mass ratio
Butane not as powerful as propane, but low vapor pressure, relatively easy to meter

Bad

Goof Off It is extremely dirty and to high octane to be useful; expensive also
Hairspray hard to meter, additives make dirty chambers
Aerosol deoderants hard to meter, additives make dirty chambers
Cleaning products hard to meter, additives make dirty chambers
Engine starters hard to meter, additives make dirty chambers, dirty burns (high octane)
Ethyne maybe too powerful; will eventually destroy pvc cannons
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Last edited by rcman50166 on Sat Jan 26, 2008 1:02 pm, edited 3 times in total.
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Unread postAuthor: DYI » Sat Jan 26, 2008 12:30 pm

Good: Hydrogen - free with electrolysis, but rather slow to produce and not as powerful as propane
MAPP - nearly ideal combustion fuel, other than cost
Ethyne (if your chamber can contain repeated DDTs) - more powerful than propane, but rather useless for hybrids
Butane - not as powerful as propane, and with a lower vapor pressure, but easy to meter with a syringe

Bad: All aerosols, including all hairsprays, deoderants, cleaning products, and engine starters - difficult to meter properly, and lots of unwanted, non-fuel additions.
Liquid fuels - difficult to meter properly, unecessary fire hazards, and generally no power advantage over gaseous hydrocarbons

REALLY bad: Ethyne (if your chamber can't contain repeated DDTs)
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Unread postAuthor: rcman50166 » Sat Jan 26, 2008 12:42 pm

THANK YOU I really didn't want this post to go to the dusty corner of the back pages. I will add them.

however hydrogen is a burdon and isn't free.(Electric Bill) But nevertheless it is powerful
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Unread postAuthor: Lentamentalisk » Sat Jan 26, 2008 1:05 pm

the deal with hydrogen is that it may be best per molar mas, but that has almost no relevance, what is more important is energy released per mol, as such small weights mean nothing.
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Unread postAuthor: Lentamentalisk » Sat Jan 26, 2008 1:23 pm

well I just did some calculations, comparing propane and hydrogen. for starters, propane burning makes 1.5 times as many moles of gas. It also releases 2x the heat. Im not taking into account the speed of the reaction, but propane seems vastly more efficient.

edit: sorry about my double post :oops:
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Unread postAuthor: jimmy101 » Sat Jan 26, 2008 2:04 pm

To avoid "retyping the wheel" you might want to check the SpudWiki page on combustion fuels first.

DYI: "Butane - not as powerful as propane". Not true, the energy content of butane and propane are virtually identical.

Lentamentalist: "the deal with hydrogen is that it may be best per molar mas, but that has almost no relevance, what is more important is energy released per mol, as such small weights mean nothing."

Not sure what you are getting at, but the most relevant parameter for comparing two fuels is the probably the Heat per mole Oxygen. The second most important parameter is probably burn speed. Hydrogen has about 15% more Heat per mole Oxygen than does propane which isn't really terribly significant. Hydrogen burns much faster (~8x) than does propane. Hydrogen reaches a peak pressure about 14% lower than does propane.

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Unread postAuthor: psycix » Mon Jan 28, 2008 5:28 am

Is hydrogen really that safe?
I always thought it was almost equvalent of acetelene considering a short DDT runup distance, a huge brisance due to a shockwave and that it should only be used in really sturdy chambers witch are basically steel hybrid chambers.

Correct me if im wrong, but I thought it was way more powerful than propane.
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Unread postAuthor: jimmy101 » Mon Jan 28, 2008 12:18 pm

psycix wrote:Is hydrogen really that safe?
I always thought it was almost equvalent of acetelene considering a short DDT runup distance, a huge brisance due to a shockwave and that it should only be used in really sturdy chambers witch are basically steel hybrid chambers.

Correct me if im wrong, but I thought it was way more powerful than propane.

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.
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Unread postAuthor: Lentamentalisk » Mon Jan 28, 2008 8:25 pm

If I am using hydrogen in a small chamber, ie: much less than a liter, would that be safe, or is it dangerous at all sizes?
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Unread postAuthor: Novacastrian » Mon Jan 28, 2008 8:31 pm

That would depend on the material used and construction of your design.
It is only dangerous if the vessel used to contain the blast can't contain the blast.
I am confident that i could use a Hydrogen fuel mix in my Hybrids but when propane or butane has more energy whats the use?
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Unread postAuthor: jon_89 » Mon Jan 28, 2008 8:59 pm

What is the best to use gasoline for a combustion? For example a spray bottle or some sort of injector. Is it more powerful than propane?
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Unread postAuthor: DYI » Mon Jan 28, 2008 9:19 pm

Gasoline is slightly less powerful than propane, and poses some obvious fire hazards if proper safety is not used. Combined with cost and availabilty issues, gasoline has few to no advantages as a fuel over propane.

As far as I have heard, pure O2/H2 has a DDT runup distance of roughly 12", compared with roughly 420" for C3H8/air. I've never heard a figure for O2/C3H8, but I would assume that it isn't as low as that of O2/H2. When using oxy/hydrogen fuel mixtures, detonation is an ever present concern. Factor in the cost and slow production rates of electrolysis, and hydrogen is only really useful if you plan on going over 200x or so hybrid mixes when propane's vapor pressure becomes an issue (tank pressure can only inject up to about 210x, and the propane mixed with air in the chamber would start liquifying around 220x). I may have f*cked up somewhere in the calcs I used to get those (I made the assumption of 120psig tank pressure), but the bottom line is that unless you plan on trying 220x in a launcher, you don't need to use hydrogen.
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Unread postAuthor: jon_89 » Mon Jan 28, 2008 10:05 pm

What about compressed gas? It would work like an engine.
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Unread postAuthor: DYI » Mon Jan 28, 2008 10:16 pm

You mean a hybrid. Any of these fuels could be used in a compressed environment (although ethyne has a nasty tendency to violently decompose on its own at over 15psig), but propane/air at 8x atmospheric pressure will still be more powerful than gasoline/air at 8 atmospheres.
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Unread postAuthor: jimmy101 » Tue Jan 29, 2008 12:26 pm

jon_89 wrote:What is the best to use gasoline for a combustion? For example a spray bottle or some sort of injector. Is it more powerful than propane?

The amount of a liquid fuel required for a typical size gun is so small that the easiest way to mesaure it is with an eye dropper. A 100in<sup>3</sup> chamber (3"ID by 14" long) needs about 2 drops of gasoline. The actual number of drops depends on the characteristics of your eye dropper.

Once you put the liquid in the chamber you need a chamber fan to make sure the fuel vaporizes and is well mixed with the air.

Using liquid combustion fuels
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