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A few questions from an amateur.

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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A few questions from an amateur.

Unread postAuthor: EternityTransfer » Sat Dec 20, 2008 4:01 am

Hello all, I'm new here, and, if no one minds, I'm gonna ask a few questions about my first ever combustion.

(Sorry about the metric units, but it isn't too hard to convert)

First off, the gun is going to have a barrel made from an as-yet-undetermined length of 63mm dia. PVC. The PVC is pressure rated to 60psi (class 6 PVC). The cannon will be the normal in-line configuration, with a barrel of 40mm PVC rated to 60psi (rating perhaps not necessary). The C:B ratio will sit at 1.5:1. The fuel used will be butane at a concentration of 3.230%, with a metered injection system. Chamber fan and spark-strip ignition from four disposable camera flash units in parallel (1400V) will also be included.

Questions:

1) The pipe is not SCH40, but is pressure rated (to 60psi). Is this OK?

2) I have heard many conflicting reports for an optimum C:B ratio, but 1.5:1 seems the one most mentioned, any suggestions?

3) Comments on the ignition source?

4) I'm not too sure what fitting/connection the butane cannister has, can anyone point me in the right direction?

Thanks for all the help. I hope this cannon will be a success.
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The butane cannister.

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Unread postAuthor: starman » Sat Dec 20, 2008 4:55 am

Hummm a 60 psi rating sounds like some weird stuff, although you will probably be ok. You'll get peak pressures in the 100 psi or so range in an optimum chamber, so your 60 psi stuff should allow for (barely) over-pressures in that range.

If this is some of that thin pvc that's used in Europe...I've seen some cracked barrels and chamber/barrel transistions using that stuff, especially while firing it in cold weather.

Don't worry about an optimum c:b ratio, it just represents overall chamber/barrel efficiency. A longer barrel will always make the cannon more powerful....a bigger chamber will always make the cannon more powerful.... :roll:

Just build yourself a 2500ish CC chamber and 1.5ish meter 40 mm barrel, something practical you can handle and transport....you'll be a happy camper... :wink:
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 20, 2008 6:45 am

You can get a cheap blowtorch or camping stove that the cannister fits into, it needs a container as the top has to be pierced for the gas to be available. I use one such blowtorch to fill a syringe which is then emptied into the chamber.
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Unread postAuthor: inonickname » Sat Dec 20, 2008 7:15 am

It looks like a propane canister used for portable bunsen burners to me. Just a note on them, never puncture a hole in a loaded one. They fly around like rockets and hurt a lot.

As for the pipe, it sounds like either thinwall or electrical conduit. Neither is very good, and it would be extremely dangerous in cold weather. Also, the thinwall stuff I have around is brittle so you're asking for shrapnel. I wouldn't risk it, just go to your hardware store and buy a length of high pressure rated, thicker walled schedule pipe.

As for a fitting for the canister, it's definitely from a bunsen burner. Maybe a chemsit/scientific sort of place may be some help with that. You probably want it to end up with a BSB fitting, as that's quite common.

As for ignition, probably just 1 camera flash dumped into a coil would work fine.


Welcome to spudfiles, and good luck :)
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Unread postAuthor: jimmy101 » Sat Dec 20, 2008 7:50 pm

Pipe rated to 60 PSI really isn't safe for a combustion. If you jamb a round in the barrel the chamber will spike to nearly 120 PSIG. You really need to find better pipe.

For the igntion were you planning on dumping the photoflashes through ignition coils? Without the coils the spark is usually to wimpy (you have to use the trigger wire from photoflash tube.)

Much easier to use a singel photoflash and a single igntion coil and just wire the spark gaps in series. (Actually, even simpler, use a BBQ piezo and 2 spark gaps).

What the heck is in that fuel cartridge? The top says "20% propan" (propane?) the side says "Butan" (butane?).
http://www.outdoorfair.de/epages/611918 ... lags167900
An injection cartridge with 70/30 butane/propane mixture. For the Campingaz 206 series. To date more than 900 million sold. 190 g.

So, it appears to be a mixture of propane and butane. The proper fuel ratio would be about [(3.23%)(70) + (4%)(30)]/100 = 3.46% if the cylinder contains 30% propane and the rest butane.
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Unread postAuthor: EternityTransfer » Sun Dec 21, 2008 6:36 am

Thanks all for the replies.

Just to clear something up, I'm not in Europe, the pic was a bit misleading, I'm actually in South Africa.

The cylinder I'm using is pure butane. (The pic is a bit inaccurate, the cylinder I have is different.)

OK looks as if I'm going to buy another length of pipe. The wall is quite thin, only 2.5mm. I figured that it would be OK because of the pressure rating, but obviously not. The piping does have a code along the length of it:
PVC-U (966-1:DPI) DUROFLO 63mm CLASS 6 PRESSURE


Changes:

1) New chamber pipe. (Expensive in SA, but you can't put a price on safety.)

2)Obtain car ignition coil.

3)Work out way to attach fuel cannister.

Thanks for all the comments, replies and help. :D
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