Spark length at 20x mix


Postby benstern » Sat Nov 04, 2006 4:27 pm

To get it to 280 psi and to speed fueling I will use a HPA tank to pressurize chamber AND to flush propane out of the fueling device.
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Postby Dumbascii » Fri Dec 15, 2006 1:59 pm

A CO<sub>2</sub> cylinder should be able to withstand the combustion pressure. DO NOT drill, cut, dent or modify the cylinder in any way or all bets are off. The only bummer is the very small exit hole at the top which will seriously limit the rate that gasses can flow out, and your ignition will have to stick in through that same hole to avoid drilling the cylinder. You could probably mount a 40' barrel to this thing to use up that relatively slow but huge volume of comustion gas. Although, the slow exit rate will probably allow the hot gasses to cool quite a bit, rapidly reducing the resultant pressure. You should definitely build this.
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Postby benstern » Fri Dec 15, 2006 6:40 pm

You miss the point a 48" cylinder rated to 3000 psi.
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Postby Dumbascii » Sat Dec 16, 2006 12:48 pm

<blockquote><i>Originally posted by benstern</i><br>You miss the point a 48" cylinder rated to 3000 psi.</blockquote>You overestimate the power of propane. Propane/air combustion does not produce a 10 atmosphere pressure increase - oxy/acetylene does. Also, 3000PSI is test pressure, not burst pressure.

Adiabatic flame temp of air/propane is 3590° F. Stoichiometric pressure increase in a closed vessel is around 8.2 atmospheres. A 20X mix would have a starting pressure of 279 PSIG, and a resultant pressure of 2288 PSI.

Since you will never achieve adiabatic temperatures or a perfect stoichiometric mix, the results would be even lower. You'd probably also have a hard time actually raising the pressure to a 20X mix. That's all if you can keep the propane from liquifying which you probably can't because it will precipitate and fill the bottom of the cylinder - even with the inrush of compressed air.

You might just put rocket fins on it and skip the spud.
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Postby benstern » Sat Dec 16, 2006 2:29 pm

The propane can't liquefy due to vapor pressure.
I know it is test pressure, that is why I said "rated"!
The stoichiometric mix would be near perfect and I will use a standard SCBA/HPA cylinder to pressurize it.
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Postby Dumbascii » Sun Dec 17, 2006 9:34 am

<blockquote><i>Originally posted by benstern</i><br>The propane can't liquefy due to vapor pressure. I know it is test pressure, that is why I said "rated"! The stoichiometric mix would be near perfect and I will use a standard SCBA/HPA cylinder to pressurize it.</blockquote><img src="http://www2.taconic.net/fkennedy/cartman.gif" align="right">Oh crap - sorry. I mistook your post as a reason <i>not</i> to do this project so I explained why you <i>should</i>. No matter what pressures you can actually ignite, this thing has the potential to be sweeeet.
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