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Hydrogen/Oxygen Mixes

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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Hydrogen/Oxygen Mixes

Unread postAuthor: shardbearer » Sat Jun 16, 2012 3:52 am

I'm thinking of making an electrolysis rig to make Hydrogen and Oxygen as fuel, preferably separately so I can do different ratios. So, what would the best H to O ratio be? 2 to 1 so that everything gets burned up? More of one to act as a buffer gas and reduce the risk of DDT? Hydrogen should be a more powerful buffer gas, increasing flame front speed and speed of sound, but would this make DDT more likely or less? Faster flame front means more likely to detonate, higher speed of sound means less. Should I use more buffer gas for higher preignition pressure?

I've heard something about butane or MAPP mixed in with both hydrogen and oxygen?

If I used lots of extra hydrogen as a buffer gas, the muzzle flash should be quite impressive. :o

What should I use to model this? HGDT won't work with either hydrogen or pure oxygen. I've heard a lot about GasEQ from DIY, but can't figure out how to work it. Which mode should I choose in the top left dropdown box? Do I have to enter the products manually? How do I know how much of each product? I want to have some idea of the pressures involved before I start building, so I can design it accordingly.
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Unread postAuthor: Alster370 » Sat Jun 16, 2012 5:30 am

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Unread postAuthor: DYI » Sat Jun 16, 2012 11:05 am

It's quite likely that the optimum mix here will be hydrogen rich for several reasons:
-lower heat capacity in hydrogen than in oxygen
-less damage to internals from fuel rich mix than from oxidizer rich mix
-higher SOS in hydrogen rich combustion products


To answer your questions on GasEq:
If you're considering launcher performance, you would be interested in the results for a constant volume. It's rarely necessary to manually select products - there's a dropdown menu which allows you to select various product sets. The only reason to manually enter products is when you're using a mix component containing an element which doesn't appear in the standard product set - for example, helium.
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Unread postAuthor: shardbearer » Thu Jun 28, 2012 2:15 pm

After lots of reading, I've decided to go the normal route of butane/propane and air. It seems that at normal mixes that would be more powerful and easier.
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