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How do I mix without a chamber fan?

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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How do I mix without a chamber fan?

Unread postAuthor: jor2daje » Thu Oct 22, 2009 5:46 pm

I have a plan for a pretty cool near semi-auto combustion, I could use a chamber fan but I am wondering what other ways there are of achieving a good mix without a fan.

Edited by jrrdw.
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Unread postAuthor: jrrdw » Thu Oct 22, 2009 6:21 pm

Drop something in the chamber and shake it around. That would be sgort87 style. :wink:
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Unread postAuthor: jor2daje » Thu Oct 22, 2009 6:37 pm

That could work, but I want this to be fairly quick to cycle, so taking time to stop and shake wouldnt be practical, I was thinking maybe some sort of vortex like nozzle for the propane to come out of so its spinning while entering the chamber.
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Unread postAuthor: Moonbogg » Thu Oct 22, 2009 7:02 pm

Perhaps a small tube with holes along the length in the chamber could evenly distribute the fuel. Maybe the holes could even be smaller at the start and larger at the end to compensate for higher pressure at the beginning of the tube.
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Unread postAuthor: hi » Thu Oct 22, 2009 8:33 pm

I have a mega combustion that shoots footballs, my cousin and i just put a length of rope in it, hanging from the center, and we just move the cannon in a circular motion for a few seconds, then shoot it.
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Unread postAuthor: D_Hall » Thu Oct 22, 2009 8:51 pm

If your system is large...

Vera uses a couple of venturi pumps(*) as fuel injectors. Seems to work reasonably well, but I acknowledge my statement is based solely upon feeling air movement; Vera has yet to be fired.





(*) mcmaster.com part 4977K12
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Unread postAuthor: Hubb » Fri Oct 23, 2009 7:33 am

The first combustion I ever built had a rope in it, similar to hi's design. The rope was affixed to the front and back of the chamber and I shook it around. It worked.
Image

The whole purpose of this design was to simulate a chambuh chain:
Image

As far as quickly mixing the fuel without a fan, a venturi would be ideal. Take moonbogg's or D_Hall's post and expand on that. In fact, I've considered something similar on the combustion I'm currently working on just so I can get rid of the batteries for the fan.
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Unread postAuthor: inonickname » Fri Oct 23, 2009 8:16 am

How about an object on a spring which is caused to shake by the previous combustion, and continues shaking to mix the fuel in a similar manner to well...a bobble head.
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Unread postAuthor: Technician1002 » Fri Oct 23, 2009 10:18 am

I am working on a metered flow rate delivery system that will meter the delivery rate of both fuel and air. They will mix into a single pipe and then the mix will displace the spent gas in the chamber for a quick repeating semi auto or full auto combustion.

The setup will include 2 of these;
Image

Both would be set to the same pressure, but the flow valves will be set to deliver the two gasses (Fuel/Air) in the proper proportion. The two regulators will have the outputs connected together in a T through check valves and the mix delivered through a single control valve. In the final configuration the flow meters and adjustable valve will be removed and replaced with calibrated gas jets. Chamber purge fill will simply be a timed cycle such as 1/2 second for a small chamber.

A variation for a large chamber will work on a pair of metering chambers. One for fuel as normal and one for air. Both chambers will be filled from regulators to the same pressure, then the outputs mixed on delivery to the chamber. This will be a 2 step metering operation to permit pre staging the gasses during the cannon reload step, followed by a quick purge fill step immediately prior to firing.
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Unread postAuthor: jimmy101 » Fri Oct 23, 2009 1:00 pm

You could scrounge up some very small ID pipe, say less than 0.01". Plumb it to several places in the chamber.

The high inlet velocity will help mixing.
Multiple injection points mean the fuel has less distance to diffuse.

The steel line used for HPLC system springs to mind. Kind of $$$ though.

McMaster #51755K31
High-Pressure Stainless Steel Tubing Type 316, 1/16" OD, 0.005" ID, .029" Wall, 5'L, $44.36 Each

A good hobby store might have more reasonably priced tubing.

EDIT:
Could also use small ID plastic tubing. That would probably be cheaper. Almost any type of plastic would work since at this ID range tubing gets to be very strong. OD is small enough that it could just be epoxied into suitably sized holes in the chamber.
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Unread postAuthor: Hubb » Fri Oct 23, 2009 1:18 pm

jimmy101 wrote:You could scrounge up some very small ID pipe, say less than 0.01". Plumb it to several places in the chamber.

The high inlet velocity will help mixing.
Multiple injection points mean the fuel has less distance to diffuse.

The steel line used for HPLC system springs to mind. Kind of $$$ though.

McMaster #51755K31
High-Pressure Stainless Steel Tubing Type 316, 1/16" OD, 0.005" ID, .029" Wall, 5'L, $44.36 Each

A good hobby store might have more reasonably priced tubing.

EDIT:
Could also use small ID plastic tubing. That would probably be cheaper. Almost any type of plastic would work since at this ID range tubing gets to be very strong. OD is small enough that it could just be epoxied into suitably sized holes in the chamber.


Do any of you remember the multiple sparking system that used to be on Advancedspuds.com (found here)? I was thinking something along those lines as far as a mixing pipe goes.
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Unread postAuthor: psycix » Fri Oct 23, 2009 1:27 pm

Nothing will mix as fast, as good and as easy as a fan.
But basically anything that causes movement inside the chamber will work.
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