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Compression Autoignition Solid Fuel Hybrid?

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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Compression Autoignition Solid Fuel Hybrid?

Unread postAuthor: auxiliary » Tue Jan 01, 2013 6:18 pm

Iv'e got an idea here and wondered if this is at all feasible. The main idea is to compress air and solid powdered fuel like flour with enough pressure and velocity to create a temperature increase high enough to combust the fuel.

In the concept drawing below I show a pneumatic ram system to push the small compression piston using air from an HPA paintball tank. I don't think it has to use a pneumatic ram but it seems like the option most likely to work.

The operation of this gun would be to first put a little powder (green stuff) in the cylinder.

Install the burst disk (purple thing) and barrel.

Open the vertically aligned valve to force the push piston (blue thing) back and when it reaches all the way back the air will then flow into the small compression cylinder at around 850psi regulated HPA.

Then shut that valve.

Open the horizontally aligned valve until the main air chamber is up to 120 psi or so.

Close that valve.

Squeeze blowgun valve to actuate sprinkler valve (green thing)

In theory the air ram will push the compression piston forward which will in turn compress the 850psi air + little bit of flour or whatever (stoichiometrically balanced of course) and ignite just by the rapid increase in pressure and temperature.

Think it could work?
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Unread postAuthor: PaperNinja » Tue Jan 01, 2013 7:33 pm

To start off, flour won't work. The whole point is that it has to be aerated, when it's in the air like powder it has a lot of surface area to burn with and stuff. If you are going to try to compress more of it into a small space, and light it it's never going to work, the flour is too compact. If you try to light a bucket of flour it's not going to happen.

Even so, you might think to use gas. In a different thread I started, ferret_guy calculated that it would take approximately TWO HUNDRED THOUSAND psi to ignite an oxygen-hydrogen mix. While that number could be changed possibly with different gases, I don't think you're going to drop by several orders of magnitude.

You could use something like diesel, which easily ignites with rapid pressure, but we're not allowed to talk about it on these forums.
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Unread postAuthor: auxiliary » Tue Jan 01, 2013 7:37 pm

Thanks for your input. That makes sense to me. 200,000psi is a lot of pressure! And I'm pretty sure it's okay to talk about using diesel because it does not fall under the category of "explosives".
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Unread postAuthor: Zeus » Tue Jan 01, 2013 7:50 pm

PaperNinja wrote:You could use something like diesel, which easily ignites with rapid pressure, but we're not allowed to talk about it on these forums.


Unless diesel is a euphemism for pyrotechnics, we can discuss it. As long as it's not a solid oxidiser, you're fine.

On topic, some powdered fuels will work, airfloat Aluminium/Magnesium/Magnalium will be interesting.
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/sarcasm, /hyperbole
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