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Detonation Powered Cannon?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Detonation Powered Cannon?

Unread postAuthor: SNDM » Sun Mar 16, 2008 3:29 am

Ive been thinking about this for a while (yes, even before that video was posted), how about a Combustion gun powered by Detonation, not Deflagation.

More power you see.

I know that roughly 20 meters of pipe (dunno the ID) can cause a Detonation when an optimum mixture of propane is ignited at one end.

Detonation happens when the flame wall travels at the Speed of Sound.

Im thinkiing of doing this with a much shorter piece of pipe, but using baffles to increase the surface area of flame exposed to the gas, so as the flames travel faster.

Does anyone have any thoughts on this, like what kind of material Id be using (Aluminium or Steel).
Thankeye greatly
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Unread postAuthor: Carlman » Sun Mar 16, 2008 8:34 am

i do not know much about combustions or hybrids but i do know that generally people try to avoid DDT dont they?
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Unread postAuthor: DYI » Sun Mar 16, 2008 8:55 am

Firstly, you need to do more research. It doesn't seem like you have any concrete plans, but are rather trying to get us to spoonfeed them to you.

Detonations produce a short-lived, quickly ocurring high pressure spike, causing a detonation wave to travel down the tube at a few km/s. With heavy (relative to the size of the detonation) ammo, you just won't be able to put that power to full use.

Every part of a detonation gun has to be able to withstand the extremely high shock loads, so any commercial fittings exposed to the combustion chamber won't last too long. You can use a piston in the tube that moves forward to protect the fueling mech before ignition, meaning that the only complex part exposed to the detonation is whatever type of pressure activated valve you use.

Steel of any kind isn't a good idea. Some materials that have been discussed are ABS, polycarbonate, lead, 2024 aluminum, and brass. Obviously, the walls would have to be fairly thick. Another possibility is a thick sleeve of one of these materials inside a steel cylinder, but the sleeve would be rather complex, and would have to be airtight.

Due to the uncommon and often expensive materials required, most det. gun designs have used relatively small chambers, and highly reactive fuel/oxidiser mixes to achieve detonation in as little as 12". If you're really serious about this design, you should be thinking along the lines of oxy/acetylene, not air/propane.

As far as I know, no det. gun designs have ever been built, because their creators realised that they are impractical, expensive, and generally not very powerful due to their small size. Their only real advantage over normal hybrids is the ability to go hypersonic, but once again, they need light projectiles to do so. If you want hypersonic, the LGG or electromagnetic/electrothermal routes are more practical in most caes.
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Unread postAuthor: jimmy101 » Sun Mar 16, 2008 2:52 pm

DYI wrote:Detonations produce a short-lived, quickly ocurring high pressure spike, causing a detonation wave to travel down the tube at a few km/s. With heavy (relative to the size of the detonation) ammo, you just won't be able to put that power to full use.

Lke DYI said, there is really not much of an advantage to a detonation gun. No extra energy in the chamber, just the much faster release of the energy.

You could probably use hydrogen and get the same affect (while avoiding DDT). Hydrogen burns about 8 times faster than propane. Of course, hydrogen also has a higher DDT propensity than does propane. Assuming no DDT, you might be able to go from a 25~50mS burn time with a ~20mS spud transit time to perhaps a 3~6mS burn time giving a faster spud transit time.
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Unread postAuthor: D_Hall » Sun Mar 16, 2008 10:28 pm

You bring up an interesting point, Jimmy....

Has there been any work towards doping propane with hydrogen as a burn rate modifier?
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Unread postAuthor: SNDM » Mon Mar 17, 2008 11:58 am

Hmmm...

Yes, I had realised just how luittle actual energy you would get from the DDT.
The thing I wasnt so sure about was the thickness of materials or types of mnaterials needed.

I suppose this would be too heavy and long, you wouldnt get much from it.
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Unread postAuthor: jimmy101 » Mon Mar 17, 2008 12:20 pm

D_Hall wrote:You bring up an interesting point, Jimmy....

Has there been any work towards doping propane with hydrogen as a burn rate modifier?

Never looked for that info specifically but I would certainly expect that many labs have looked at mixing various fuels in ICEs, jet turbines, PDEs, guns etc.
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Unread postAuthor: ispudder » Sun Mar 30, 2008 12:23 pm

not to hack this thread or rain on anyone's parade but shouldn't this be in the combustion forum instead?
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