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Butane/Oxygen/Hydrogen mix?

A place to ask general spud cannon related questions.
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Unread postAuthor: Alster370 » Sat Oct 15, 2011 5:15 pm

You'd just pump the gases into the long thin copper piping, using a pump like the one I built.


Wouldn't that give the pump a huge dead volume? as well as adding a large amount of ambient air to the cartridge? :?
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Unread postAuthor: Alster370 » Sun Oct 16, 2011 9:19 am

Bump:

Since its still a week or so before I make a cartridge and try out this mix, I thought I might as well get some feedback from you in relation to my cartridge design.
Image

As far as I can tell, the only problem may be with the nichrome wire deteriorating due to the combustive mixture and the fact that it is very thin (36awg)

P.S: Oh, I have forgotten on the diagram that the Cartridge body is T6 aluminium.
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Unread postAuthor: Gun Freak » Sun Oct 16, 2011 11:05 am

Sorry if this has already been mentioned, but how are you going to connect to the schrader if barely any of it is exposed?
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Unread postAuthor: saefroch » Sun Oct 16, 2011 1:04 pm

So as the pump is concerned, so long as the copper piping comes after the check valve, there will be no effect upon dead volume. There is some really thin copper piping you can get, probably 1mm, that would work well.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 17, 2011 12:34 am

I have mixed feelings about nichrome wire.

I got it to work in a combustion, but never in a hybrid. Then again, I don't remember if my failure with the latter was due to an incorrect mix because I hadn't yet figured out that the pump's dead volume was an issue. For hisBACHdaccel certainly got good ignition with steel wool.

Hmmm, this might warrant some more testing...

saefroch wrote:So as the pump is concerned, so long as the copper piping comes after the check valve, there will be no effect upon dead volume.


All volume after the pump's check valve needs to be taken into account when calculating how much fuel to inject, in my shock pump I found this to be 1.75mL, insignificant for a large project but for a small cartridge this will have a huge effect and indeed is the reason why my initial hybrid projects failed to ignite.
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Unread postAuthor: Alster370 » Mon Oct 17, 2011 10:34 am

I just think its a lot less fiddly when It comes to installation and reliability than a spark gap. :? My only concern is that the combustion mix will destroy the wire eventually.

Sorry if this has already been mentioned, but how are you going to connect to the schrader if barely any of it is exposed?


Well it would have to be more exposed if I were to use a pump, but to be honest I would feel safer using a syringe to fuel and it would be more accurate. The shrader doesn't need to be exposed nearly as much because the syringe tip is going inside the shrader itself. An o ring would have to be epoxied at the thickest of the syringe tip to ensure a good seal.

Has nobody got any problems with me using nylon as endplugs? It seems to have identical(if not better) suited properties for this kind of use and is a fair bit cheaper.
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Unread postAuthor: Alster370 » Sun Oct 23, 2011 4:04 am

Might as well give a small update as parts arrive....

Image
Big ass syringe :D

Image Aluminium cartridge cases, 25mm OD 21mm ID, 6" long. type: en aw 6060. Would anyone be able to give me a max mix when using these aluminium tubes? Heres a data sheet, was quite hard to find :http://www.cosmosaluminium.gr/pdf/alloy_data_sheet_6060.pdf


Image Used presta to schrader converters instead as they are much cheaper than the actual valves but obviously have the schrader thread im looking for. Im using them as the burst disk holder for my cartridges.(see ilovefire's cartridges for a working example).
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Unread postAuthor: DYI » Sun Oct 23, 2011 10:20 am

The maximum allowable pressure for those tubes will be ~0.18*σ<sub>max. allowable</sub>. You can use GasEq to find out what mix that will require, and the data sheet to determine what maximum stress you're comfortable with for this application. The datasheet is, of course, useless to the rest of us because you neglected to mention the temper of the tubes you're using.

This may have been mentioned elsewhere in the thread, but try to use the largest diameter nichrome wire which your power supply can heat. If oxidation is still a problem, you may wish to look into diesel engine glowplugs. Their heating element is made of refractory metals with high resistance to oxidation, and they survive ~20X quite nicely.
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Unread postAuthor: Alster370 » Sun Oct 23, 2011 11:09 am

Sorry for not metioning the temper, I would of if it was stated on the sellers eBay page :?, So I have contacted him for an answer.

I planned to go up to an equivalent of 30x air using my mixture should the materials take the pressure. However I would be happy to go higher, my main concern is finding a cheap burst disk rated for 1500psi+, It may even have to be a steel disk cut from a sheet.

Im trying with steel wool for now, but I will get some nichrome when Ive done a bit of testing. I am aware that 32awg nichrome wire needs 1.36 to reach just shy of 1000F, so i will probably go with a x9 AA rechargeable battery pack.
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