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Syringe fuel injection?

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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Syringe fuel injection?

Unread postAuthor: OneIntervention » Sun Jan 08, 2012 12:49 am

Hey guys, I've reached a sort of stall here with the development of my first Spudgun. I've been having a debate with my dad about the Syringe loading system which I was planning on using. He says the syringe injection system does not work, as the Butane will escape from the Syringe when it is removed from the refill can, going so far as to title This video a hoax.

Thoughts?
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Unread postAuthor: warhead052 » Sun Jan 08, 2012 12:50 am

Just try it. If it works for us, why won't it work for you?
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Unread postAuthor: OneIntervention » Sun Jan 08, 2012 12:57 am

I've been trying to tell him this, but he won't have it. What he wants is cold, hard proof.
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Unread postAuthor: warhead052 » Sun Jan 08, 2012 12:59 am

Well, go out and get a syringe your self. Its not that hard. Look for jsr's see through combustion. I believe he included a video of him metering and injecting as well as firing.
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Unread postAuthor: OneIntervention » Sun Jan 08, 2012 1:13 am

I can't find it, would you mind posting a link?
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 08, 2012 1:31 am

It's counterintuitive but you have to think of the gas in the container as having fluid properties.

Here's an example to show your dad:

[youtube]http://www.youtube.com/watch?v=Xzfq3lIWu9s[/youtube]

CO<sub>2</sub> in a flask can be poured like a liquid.

You can do this yourself at home, many other examples on the web:

[youtube]http://www.youtube.com/watch?v=lNbHjKqt4BY[/youtube]

By the way, as it was blocked in some countries, I reuploaded the syringe tutorial without audio:

[youtube]http://www.youtube.com/watch?v=EoVDuh3ziNg[/youtube]

A quick experiment you can do, fill a syringe, and let it sit for 5 minutes with the nozzle open. Then squirt it (carefully!) in to a naked flame, and tell me if the butane escaped ;)
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Unread postAuthor: Technician1002 » Sun Jan 08, 2012 5:57 am

Butane will diffuse out of the syringe over an extended period of time. The time between filling it it and dispensing it into your chamber results in negligible loss.

Srynge fueling worked fine for my only combustion.
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Ignition on the first try.
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Unread postAuthor: warhead052 » Sun Jan 08, 2012 11:04 am

jackssmirkingrevenge wrote: Then squirt it (carefully!) in to a naked flame, and tell me if the butane escaped ;)


Haha I have done that multiple times just for the hell of it. Its so fun. Until you burn your finger, but its still fun. And I recommend using a candle and not a blow torch or anything for it to really work well.
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Unread postAuthor: jimmy101 » Sun Jan 08, 2012 11:57 am

Yes, butane will diffuse out of the syringe ... if the syringe is actually open to the air! (well duh)

Easy enough solution, put your damn finger over the end of the needle (hence a blunt needle is a good idea and is generally available wherever you get the syringe) or the tip of the syringe. The plastic syringes most people use are basically air-tight except at the opening of the needle.

Heck, if there is a needle you probably don't even need to cover its tip. Diffusion down an inch or so long pipe with an ID of less than a mm is going to be extremely slow.

Gas diffusion is a surprisingly slow process. So slow that that is the main benefit of a chamber fan. It takes tens of seconds, if not a couple minutes, for the gas load to fully diffuse throughout a typical sized combustion chamber. If you fire without letting the fuel fully mix the performance goes way down. A fan will mix the fuel fully within a couple seconds.

Heck, I've even roughly measured how fast propane diffuses. It is pretty slow. (http://www.inpharmix.com/jps/Propane_dif_polycarb.html)

It is safe to say that if the end of the syringe is covered the rate of fuel loss from the syringe is measured in terms of months if not years. It is also safe to say that once injected into a gun's chamber it will take tens of seconds up to a couple minutes for the fuel to fully disperse though out the chamber (without a chamber fan).

So tell your dad he is wrong and build the stupid cannon.
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Unread postAuthor: OneIntervention » Sun Jan 08, 2012 2:37 pm

Thanks for the replies guys,
@jack, actually, that last video with the demonstration, that's the one he called a hoax. Thanks for the vids!

@Technician, I've been telling him that the loss is negligible, but he doesn't get it.

@warhead (and jack), I actually tried this, and I got a nicely sized flame. He said that it's a flame, but not enough to push a potato out of a barrel.

@jimmy, I did this, but he says the time it takes to take the syringe off the butane tank and to put your finger onto it, all the butane is already lost.

He says I can build it using the syringe injection system, just for me to learn it won't work. The look on his face when it works is going to be priceless.

Thanks to all of you, and expect me in the Combustion Cannon Showcase!
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Unread postAuthor: jackssmirkingrevenge » Sun Jan 08, 2012 2:40 pm

OneIntervention wrote:that last video with the demonstration, that's the one he called a hoax.


Well, I bloody made it, and I can tell you it works :)

Here's the launcher thread with much more shots from the same launcher, all fuelled in the same way.

He says I can build it using the syringe injection system, just for me to learn it won't work. The look on his face when it works is going to be priceless.


FOR SCIENCE!

good luck :)
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Unread postAuthor: Gun Freak » Sun Jan 08, 2012 2:55 pm

Ahh good luck... Can you please video his reaction :D
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Unread postAuthor: OneIntervention » Sun Jan 08, 2012 3:05 pm

Ah don't worry guys, I'll have the whole thing documented :)
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Unread postAuthor: Crna Legija » Mon Jan 09, 2012 1:50 am

OneIntervention wrote:He says I can build it using the syringe injection system, just for me to learn it won't work. The look on his face when it works is going to be priceless.


just make sure you get the amount off fuel right on the first shot lol.
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Unread postAuthor: pneumaticcannons » Mon Jan 09, 2012 6:13 am

The look on his face when it works is going to be priceless.

My dad is almost as stubborn. I've gotten to enjoy that look many, many times.... You'll love it :D
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