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Cheap fuel system

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Cheap fuel system

Unread postAuthor: fatcat6 » Thu Sep 25, 2014 1:40 am

I've seen the basic hairspray design and i wanted to build something that would put the right amount of gas in the chamber. I don't have the time to ship all the parts for the metered propane system so i came up with my own idea. I found these butane refills :arrow: :http://www.bernzomatic.com/item.html?id=66 They're 13.3 mills or .44 ounces.

My plan is to calculate how much butane should go into my combustion chamber and inject it in with the pressurized liquid butane and because i can see into the refill, I'll draw lines for each shot. First i calculated the volume of my combustion: chamber :arrow: http://www.onlineconversion.com/object_ ... r_tank.htm

Next I found I needed only 4% of the chamber to be filled with butane (gas) for the most power, (my combustion chamber required about 210 cc of butane or 12 cubic inches (gas form) and then finally I found the butane liquid to gas ratio: http://encyclopedia.airliquide.com/ency ... sp?GasID=8

After all that research, My potato cannon should get maximum power with .85 mills of liquid gas which will then turn into 210 cc of gas. The butane refills are about 6cm or 2.3 inches long and they're a symmetrical shape so i divided 13(butane refill size) by (.85 gas used per shot) and got about 15 which means one refill will have 15 shots in my case. Lastly i cut a refill piece out of a lighter and stuck it on my potato gun and drew 15 lines on the butane refill( because the refilling cartridge is clear i can push the refill in until the butane level has reached the line)

So I havn't tested this but do you guys think it will work? any suggestions?
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Re: Cheap fuel system

Unread postAuthor: jackssmirkingrevenge » Thu Sep 25, 2014 5:38 pm

have a look:

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Re: Cheap fuel system

Unread postAuthor: fatcat6 » Fri Sep 26, 2014 12:18 am

yeah that looks like a good system but isn't 3 or 4% of the chamber meant to be filled with butane in gas form not liquid form? I think the butane liquid to gas ratio is about 1:200.
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Re: Cheap fuel system

Unread postAuthor: jimmy101 » Thu Oct 02, 2014 5:09 pm

The syringe fills with gaseous butane. The syringe is then burped (vented to the atmosphere) for a second or so to set the gas's pressure to be the same as atmospheric (required to get the correct volume of gas).

The advantage of using gaseous fuel is that you measure a volume that can be measured with reasonable accuracy. The problem with liquid fueling is it is very difficult to accurately measure 0.85 ml of a liquid that wants to vaporize the instant its pressure drops anywhere near atmospheric.

Your approach will work but I doubt it'll be all that accurate or reproducible. It is easier to do it like Jack describes or something like this;Image
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