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hybid igniton

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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hybid igniton

Unread postAuthor: c11man » Mon Mar 02, 2009 7:06 pm

i am in the dreaming stage of a hybrid and i was wondering if there is much or any diffenence between having the ignition source in the miiddle of the chamber or at the end of it. also i was wondering how long could you make a 2inch chamber with out having the danger of ddt oh i almost forgot this cannon would be fired at a max of 10x
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Unread postAuthor: CasinoVanart » Mon Mar 02, 2009 8:28 pm

You could make a two inch chamber rather long (over twenty feet) and still not worry about ddt at 10x mix.

The difference between having the ignition at the back vs middle is simple, when it's in the middle you have two flame fronts and a lower chance of ddt (ddt is way overated). Most people however find that placing the spark at the rear is a lot easier than placing it in the middle, myself included, you won't compromise the integrity of the chamber if you place it at the rear either.
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Unread postAuthor: c11man » Mon Mar 02, 2009 10:11 pm

oh that is good to know about the ddt danger and the camber wouldnt be compremised because i would use a tee in the middle instead of drilling and tapping into the pipe.
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Unread postAuthor: starman » Mon Mar 02, 2009 11:08 pm

With the gap in the middle, those 2 flame fronts also cause the chamber to burn roughly twice as fast as if the flame starts at one end and has to propagate the full distance of the chamber.

The multi gap advantage is also very real but the critical issue there again is precise placement of the gaps in the chamber. Think multiple flame fronts simultaneously burning fuel/air in different locations of the chamber.

This effect makes the chamber combustion act like a faster valve would in a pneumatic model.
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Unread postAuthor: jimmy101 » Tue Mar 03, 2009 12:57 pm

The affect of multiple gaps, and/or position of a single gap, are much less critical in a hybrid than they are in a standard combustion gun.

The burst disk, if designed to rupture near the theroetical peak pressure, will pretty much override the affects of different number and position of the spark gaps. Doesn't really matter how fast the fuel burns since the burst disk "gates" the pressure to the ammo/barrel once combustion has proceeded far enough. If combustion is slow (for example from a single spark) it doesn't matter since that just means there is a longer time delay before the disk ruptures.
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Unread postAuthor: starman » Tue Mar 03, 2009 1:09 pm

Yep true, although based on HDGT, gap count can still make a significant performance difference in a hybrid, especially if the peak pressure burst disk break point isn't possible or practical.

Lots of other complexities as well, ammo mass, c:b ratio, play into it...
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Unread postAuthor: c11man » Tue Mar 03, 2009 9:35 pm

thanks for the help starman
:D
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