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Acetylene as a Propellant? (Safe/Not?)

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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Acetylene as a Propellant? (Safe/Not?)

Unread postAuthor: Dr meat201 » Sat Apr 10, 2010 9:24 pm

Has anyone looked into Acetylene as a fuel source? I'm thinking that it would probably be dangerous, but it can be made relatively easily (If you don't know how it's made, that's probably best...). I'm much more comfortable in the pneumatics section, so this was purely a curiosity question for those who are more experienced with combustion cannons.
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Unread postAuthor: inonickname » Sat Apr 10, 2010 9:46 pm

If you build your cannon correctly using the correct materials then it's very safe. Things such as PVC insulation on copper wire should be avoided, and preferably copper in general (silver as well :lol: ).

Asides from that, it must be kept at very low pressure- taking it up to even 20 psi is very unsafe.
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Unread postAuthor: DYI » Sat Apr 10, 2010 9:48 pm

Acetylene is an acceptable, and rather entertaining fuel for an all-metal combustion cannon of robust construction. It has a nasty tendency toward detonations, which sound great but rip normal plastic pipe to shreds. Which then proceed to rip YOU to shreds.

It's fairly energetic, as gaseous fuels go, but its instability makes it unsuitable for hybrids, and is thus easily overtaken by propane.

It has been used as a fuel source before, and is very easy to ignite (no s*** :roll: ) even if the fuel mix is off a bit. However, due to the requirement for much sturdier construction than that of a "normal" spudgun, it is not in widespread use.

Inonickname's comments on its chemical incompatibilities are correct, and the compounds which may form if they are ignored are not to be trifled with.
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Unread postAuthor: Moonbogg » Sun Apr 11, 2010 12:41 am

I asked the same question when I was new here. I wanted to make an all metal Acetylene cannon and people were able to convince me that even more power can be had from propane in hybrid configurations and safer at that. But yes, people use it sometimes, either by itself or mixed with O2.
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Unread postAuthor: DR » Sun Apr 11, 2010 1:33 am

Years ago, when the Spudtech forums were still active, we would always warn potential users against using acetylene as a propellant.

I'm not absolutely positive, but it takes only (something in the range of) 1/500th of the static energy you would generate, by walking across a carpet, to ignite the acetlyene gas.

Acetylene is dissolved in acetone in th porous filling of the tank. It is NOT stored as a compressed gas, because if that is done it can/will explode at any pressure above 15 psig. If you draw more than the 1/7 of the cylinder size per hour, acetone from the tank is drawn out and may damage the regulator, hoses and seals. The flame will sputter. If too much acetone is removed, the tank can explode when subjected to rough handling after use. Acetylene is a dangerous material and needs to be handled with respect ~ Reference: <a href="http://www.anvilfire.com/FAQs/gasfacts.htm"target=_blank">Gas Facts</a>


With the dangers involved and the great care that must be taken to handle the acetylene gas, the only benefit provided, is the added "WOW Factor" of using something much more unstable than the norm.
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Unread postAuthor: inonickname » Sun Apr 11, 2010 2:00 am

As a side note, the safest use of acetylene would be in a carbide cannon. The acetylene is made in the gun then used immediately. There's no projectile and little overpressure risk.
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Unread postAuthor: jimmy101 » Sun Apr 11, 2010 5:07 pm

What DR said. Why diddle with Acetylene? It's a hair (as in 10%) more powerful than propane and burns a bit faster.

But, heck the cylinder it is shipped in is filled with crushed brick to keep it from spontaneously exploding. (Acetylene will explode even without an oxidizer, like air, around.)

Want 10% more power in your gun? Make the chamber 10% bigger.

Any fuel related question is probably already answered on the SpudWiki fuel page. Search the wiki for "common fuels" and you should find the page. (Currently the wiki appears to be dead, "common fuels" returns an error. ) :cry:

Most of the info in the wiki is also at;
http://www.inpharmix.com/jps/Combustion_fuels.html
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Unread postAuthor: grock » Sun Apr 11, 2010 11:25 pm

inonickname wrote:As a side note, the safest use of acetylene would be in a carbide cannon. The acetylene is made in the gun then used immediately. There's no projectile and little overpressure risk.


actually, wasn't there a topic about carbide cannons shooting soccer balls or something? some yearly event in a European country?
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Unread postAuthor: Technician1002 » Sun Apr 11, 2010 11:37 pm

inonickname wrote:Asides from that, it must be kept at very low pressure- taking it up to even 20 psi is very unsafe.


This is the reason that regulator settings are marked in RED on the gauge.

From the Wikipedia article on welding;

Acetylene is the primary fuel for oxy-fuel welding and is the fuel of choice for repair work and general cutting and welding. Acetylene gas is shipped in special cylinders designed to keep the gas dissolved. The cylinders are packed with porous materials (e.g. kapok fibre, diatomaceous earth, or (formerly) asbestos), then filled to around 50% capacity with acetone, as acetylene is acetone soluble. This method is necessary because above 207 kPa (30 lbf/in²) (absolute pressure) acetylene is unstable and may explode.


This is not a gas to play with. Note the 30 PSI noted in the Wikipedia, this is Absolute pressure, not guage pressure. At sea level, this is about 15 PSI.
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