Making a speical effect -the fire ball.

[)DEMON(]

Which brings me to another question, what material should the burst disk be made out of to achieve the best bang? I think latex sheeting would work well.

[jackssmirkingrevenge]

Foil is probably a better idea as it would tend to fragment as opposed to tearing like latex would.

[)DEMON(]

What is a good method of inserting the tinfoil into the onion?

Last time I tried it was such a mission to get the damn thing in and it didn't even work very well.

[starman]

I have a hard time beliving a simple combustion will burst the burst disc with ~100PSI pushing on it from the other side.

You'll need to use a 60-80 psi burst disk with a 1X advanced combustion, 100 is too large. My noise cannons are based on a roughly 60-70 psi burst disk setting. A combustion burst disk cannon is a LOT louder than a pneumatic burst disk at similar psi setting. You get much more of a boom sound with a combustion. While loud in its own right, the pneumatic however tends to give off a less impressive snap or pop sound.

Which brings me to another question, what material should the burst disk be made out of to achieve the best bang? I think latex sheeting would work well.

I'm using 3 layers of 2" Scotch Blue painters masking tape over a 2" male camlock coupling. Like this...


The tape disintegrates into lots of little blue chunks like the one on the floor beside my thumb.

[psycix]

The reason combustions may sound louder, is that the gases are hot, and thus flow out faster.

[)DEMON(]

Thanks for the advice guys, I will post some pics of my progress though out the next month.

I don't think a hybrid would be to difficult to do, essentially a hybrid is a multiplication of the propane and air mixture by a certain factor right?

Then what would happen when you reach the pressure at which propane liquefies?

[psycix]

Then you'll get liquid propane in your chamber, and everything screws up.

[)DEMON(]

So how do they prevent liquification at higher mixes?

[DYI]

Then what would happen when you reach the pressure at which propane liquefies?

Depending on the ambient temperature, that would occur somewhere in the vicinity of 170x (almost 2700psi precharge). If you're going to try that any time soon, let us know. If you did hit such a high pre-ignition pressure, propane would begin to condense on the chamber walls, throwing off the fuel mix.

No one needs to prevent liquification at higher mixes, because no one* has a hybrid capable of 2700 psi precharge.

[rp181]

Are you sure DYI.....?

Dont forget about partial pressure, whenever theres a mixture of gasses, it wont liquify for the pressure of one part.

[psycix]

I think he already included that, since a pure propane mixture would liquefy on about 100 psi, depending on the temperature ofcourse.

[)DEMON(]

So why is it that propane you buy commercially in metal containers is in liquid form yet has an output gas pressure of around 100psi?

** Nevermind, silly me. I was thinking of a homogeneous mixture of propane. Instead of air and propane.

I would like to know one thing though, how likely is it for a premixed combustion/hybrid to go off accidentally? If we exclude the actual cannon construction and include human nature.

[DYI]

I would like to know one thing though, how likely is it for a premixed combustion/hybrid to go off accidentally? If we exclude the actual cannon construction and include human nature.

In this case, it depends on the person operating it. Obviously, a lot more stable than nitroglycerine or TATP, but a lot less stable than, say, TNT.
It won't be set off by sudden shocks or any reasonable static electric discharge (not including Van de Graaf generators or lightning, of course), unless you're using hydrogen or acetylene, in which case such charges would be a real concern.

Basically, I'm only scared being near a hybrid when someone is standing close to the trigger

[psycix]

In this case, it depends on the person operating it.

Fully agree on that since cannon construction is left out.
But )DEMON( do note that the way of cannon construction plays a role. A good example is having a BBQ igniter on the back end of the gun: if you put the gun down on its butt while loaded, it fires.

Basically, I'm only scared being near a hybrid when someone is standing close to the trigger

I am afraid of a loaded hybrid even when no one is close to the trigger. Imagine that the disk fails on a 20x mix, maybe because of a mechanical shock the disk just got what it needed to burst.
Even if it doesn't ignite, the 19 bar pneumatic shot can be devastating.