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Dieseling mini hybrid cartridge idea

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Dieseling mini hybrid cartridge idea

Unread postAuthor: McKlane » Thu Oct 24, 2013 12:14 am

Hi people.

I have been trying to come up with a miniature cartridge cannon that could be used to make a powerful semi-auto handheld spudder.

If the barrel is very short, dieseling could actually be beneficial, no? Because the problem with ddt is the brief but excessive pressure. In a short barrel, that is not as bad, which is the same reason why pistol powder has to be fast and the barrel strong.

Here is what I came up with. But I think somebody must have already done this. So my question is why will it not work? :) Or has somebody already done this but in a better way?

Here is how it would work:

The diesel is carefully measured and dropped into a small recess in the bottom of the lead sabot. The sabot is then pushed into the inner pipe until it sits securely in front of the burst disk. The air pressure behind the burst disk is high, but lower than the diesel ignition pressure.

When firing, a rod (the "hammer") rapidly pushes the sealing plug into the cartridge, raising the pressure of the air inside the cartridge. The burst disk is chosen to burst at a pressure slightly higher than the diesel ignition pressure. So, as soon as the burst disk bursts, the diesel will ignite and detonate.

I think the "hammer" could be operated from a high pressure air chamber at perhaps 1000PSI, way above the pressure needed to ignite the diesel. This air will only be used to push the "hammer" so it will never be in contact with the diesel.

(By the way, this is a HPA/liquid fuel hybrid, but not an airgun, so that is why I post it under hybrids)
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Re: Dieseling mini hybrid cartridge idea

Unread postAuthor: dart guy » Thu Oct 24, 2013 5:50 am

The idea you just submitted was awesome, but not a hybrid. You just made a burst disk pneumatic which could easily be made hybrid by having a wire that would get got from electric current or have the plug be a spark plug thing.Also, i would like to know why you built a foster slug to launch a tiny insignificant piece of potato when you could have solid point or a plastic split er point. also i think you may need to experiment with the liquids.
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Re: Dieseling mini hybrid cartridge idea

Unread postAuthor: Labtecpower » Thu Oct 24, 2013 6:02 am

Should work I think, basically the same system as a fire piston.
But why the lead sabot? If you put a piece of potato on the tip the potato will decelerate before the lead does.
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Re: Dieseling mini hybrid cartridge idea

Unread postAuthor: cammyd32 » Thu Oct 24, 2013 3:47 pm

dart guy wrote:The idea you just submitted was awesome, but not a hybrid. You just made a burst disk pneumatic which could easily be made hybrid by having a wire that would get got from electric current or have the plug be a spark plug thing.


Technically it is a hybrid. Because the power comes from a pressurized mix of fuel and air at pressures greater than 1 atmosphere, that makes it a hybrid.
He wouldn't be using a spark as a source of ignition, instead his design uses the auto-ignition of the diesel to ignite the mix, have a read

The design, In theory looks great, in practice it will be quite a task to build and get it running reliably enough for any semi auto action, although I suggest doing away with the measly bit of potato and just fire that big ass bit of lead!
I like the concept though. :)
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Re: Dieseling mini hybrid cartridge idea

Unread postAuthor: jackssmirkingrevenge » Thu Oct 24, 2013 4:30 pm

Is it just me or is the lead "sabot" actually the projectile and the potato just a nominal inclusion to qualify it as a potato gun :D

Well, you said "non discarding"... does something stop it from leaving the barrel?

The theory looks sound enough, implementation will be a challenge. Some sort of pop-off mechanism would allow you to do away with the burst disk, and have the diesel already in contact with the air when compression begins, making ignition more likely.
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Re: Dieseling mini hybrid cartridge idea

Unread postAuthor: Fnord » Fri Oct 25, 2013 10:00 am

If your hammer is moving sufficiently fast you won't even need a burst disk. Your "sabot" should be a tight fit though.

One other thing to keep in mind is the ratio of hammer mass to projectile mass; you don't want the hammer to move backwards any more than it has to when the mix ignites.
I am not sure of the intricacies of dieseling guns- you'd best start off by looking up spring-powered airguns which can produce this effect and base a prototype on them.
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