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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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Unread postAuthor: jimmy101 » Fri May 18, 2007 12:38 pm

By my calculations Hydrogen has slightly more energy per mole than do most other fuels. Slightly as in ~10%.

Hydrogen burns much quicker than most fuels at atmospheric pressure. At elevated temperatures and pressures (i.e., part way through combustion) flame speed isn't much faster than other fuels.

The peak adiabatic pressure is a little lower than other fuels (~10% less than propane) but the peak temperature is a little higher.

Hydrogen is more likely to do deflagration to detonation transistion than most other fuels.

A <A href="http://www.spudfiles.com/spudtech_archive/viewtopic.php?t=15671">bunch of stuff</a> about fuels.
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Unread postAuthor: dongfang » Sat May 19, 2007 3:45 pm


OK, good point to consider the oxidizer as the limiter, not the fuel.

Anyway, if there are x moles of O_2 in some chamber:

After a stoichisometric injection of hydrogen, according to the link above, (1-29.5%)x = 0.705x moles of O_2 should remain (assume athmosperic chamber charge pressure. If you do hybrid, just multiply x by the final charge pressure in bar).

That is, heat of combustion is 119 kCal / mol * 0.705 x moles = 83.9 x kCal.

With, say, butane, it is
(1-3.67%)x = 96.33x moles of O_2 * 105 kCal / mol = 101.15 x kCal.

So, still some more energy (as if combustion heat was all there was to it, I know it is not...) in the butane. The large volume of the tiny mass of H_2 displaces about a third of the oxygen.

Of course, by all means play with the hydrogen & have fun... but do not expect any performance miracles.

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Unread postAuthor: boilingleadbath » Sun May 20, 2007 6:20 pm

Indeed, dongfang.

Energy density has the potential to mislead, so I suggest farming the math out to a more comprehensive utility, like gaseq.

(which, incidentally, supports your analysis)
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