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The Combustion Machine Gun

A place to ask general spud cannon related questions.
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Unread postAuthor: jimmy101 » Sat Aug 15, 2009 2:36 pm

inonickname wrote:I did not say "extremely", I said "very". It can cause blindness through skin contact and ingestion. If you want that, then good for you. I was just highlighting another issue with this non-working idea.

I've worked with thousand of gallons of MeOH, usually in small lots of a couple gallons or so at a time. Toxicity just isn't a problem. Doesn't matter if you say "midly toxic" or whatever, heck water is "midly toxic". Toxicity just isn't a big issue with MeOH. Pour it over your hand... no problem. Do it every day for a month ... no problem (I know because I've done it). Drinking tens of ml or more is a problem. Blowing tens of ml's into your eyes is a problem. But that level of toxicity occurs with all kinds of things, gasoline, terpentine, acetone, etc. Used motor oil is considerably more toxic than is MeOH but folks let it run down over their hand when changing the oil in a car.

Actually nah, you don't know. There are big differences between a 2-stroke and a pulsejet.

Yep, differences but also a lot of similarities. Both exhaust waste gases and intake fresh air via the same port. A 2-stroke compresses it's fuel, but only because of the mechanics of a typical 2-stroke engine, compression isn't a requirement of the combustion cycle. A 2-stroke engine can be ignited via a spark plug (which doesn't require the fuel compression) or as a diesel cycle (which does require compression). A pulse jet can be ignited by flame suck back, or hot chamber parts, or a spark plug.

A typical combustion spud gun probably goes a long way to auto-purging itself of spent gases during it's normal combustion cycle. That is, 2 seconds after firing the chamber does not contain 100% combustion gases, I would WAG that the gases in the chamber are perhaps 50% fresh air and 50% combustion gases by the time the "bang" of the gun has died out.

So put a magazine onto the barrel. Design the mag so that it feeds a round when the barrel pressure is low, that is, when the gun is sucking air back into the chamber. Include a stop so the ammo isn't sucked all the way back into the chamber. Timing would be tricky but not impossible.

During the firing cycle it looks like a generic combustion spudgun. During the combustion phase there isn't really anything special about a pulse jet, just fuel burning and expanding. It's the same with or without ammo in the barrel.

Once the ammo leaves the barrel a combustion spud gun behaves exactly like a pulse jet in terms of sucking fresh air back into the chamber. If fuel is injected during the suckback phase then there is no reason you can't get the combustion process to cycle. You might need a spark plug or you might be able to get a small amount of flame suckback to ignite the next cycle.

1. During the combustion cycle all three devices (2-stroke, pulse jet, combustion spud gun) are similar. All will work with a load or without a load. All three will work with or without compression.

2. Once the ammo has left the barrel the gun looks exactly like a pulse jet. Once the 2-stroke piston has opened the exhuast port the 2-stroke looks just like the gun and the pulse jet. All three devices will first blow out the exhaust products then suck back some fresh air into the chamber. The trick is getting enough air and the right amount of fuel. But that isn't really unique since basically all combustion devices have to solve the problem of the fuel to air mix.
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Unread postAuthor: jackssmirkingrevenge » Sat Aug 15, 2009 2:47 pm

jimmy101 wrote:I've worked with thousand of gallons of MeOH, usually in small lots of a couple gallons or so at a time. Toxicity just isn't a problem. Doesn't matter if you say "midly toxic" or whatever, heck water is "midly toxic". Toxicity just isn't a big issue with MeOH. Pour it over your hand... no problem. Do it every day for a month ... no problem (I know because I've done it). Drinking tens of ml or more is a problem. Blowing tens of ml's into your eyes is a problem. But that level of toxicity occurs with all kinds of things, gasoline, terpentine, acetone, etc. Used motor oil is considerably more toxic than is MeOH but folks let it run down over their hand when changing the oil in a car.


Ditto, we regularly work with hundreds of litres at a time, both as a solvent for reactions or for cleaning, and I'm still here :)
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Unread postAuthor: Biopyro » Sat Aug 15, 2009 2:50 pm

This has sort of already been done, I'm suprised no-one's linked it already.
http://www.spudfiles.com/forums/auto-t1278.html
He used an external air supply which meant 3 ports were needed, but still almost auto.
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Unread postAuthor: smiley_666 » Sun Aug 16, 2009 2:56 am

jimmy101 wrote:
Actually nah, you don't know. There are big differences between a 2-stroke and a pulsejet.

Yep, differences but also a lot of similarities. Both exhaust waste gases and intake fresh air via the same port.

not in any 2-stroke motor ive ever seen... they have both a intake port and exhaust.
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