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Cartridge Concept (Oxygen+Fuel "Hybrid")

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: Insomniac » Tue Oct 12, 2010 7:59 am

Sodium Bicarbonate is a better alternative to NaCl, and is probably the best thing that you'd have lying around in the pantry...

...However, as you work in the lab and all, go with the sodium hydroxide. :)
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Unread postAuthor: POLAND_SPUD » Tue Oct 12, 2010 9:31 am

it's going to be adopted by NATO or something
lol I second that.

Oh btw... the way I understand it... if you use more oxygen then you get more power with lower mixes, right ? Is it more less along the lines of 3 times more oxygen gives 3 times more power?

Does this affect spark gap in the same way as using higher mixes does?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 10:05 am

Oh btw... the way I understand it... if you use more oxygen then you get more power with lower mixes, right ? Is it more less along the lines of 3 times more oxygen gives 3 times more power?


If you fill the cartridge completely with oxygen then add the butane, you can only get about 5x mix maximum (because oxygen is around 20% concentrated in the atmosphere), but since it's not pre-pressurised I'm not sure that it's the equivalent of having a 5x quantity of butane in 60 psi.

Does this affect spark gap in the same way as using higher mixes does?


Since you're still operating at atmospheric pressure, gas particle density should remain the same meaning the same spark gap as an ordinary combustion would suffice.
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Unread postAuthor: Ragnarok » Tue Oct 12, 2010 10:06 am

POLAND_SPUD wrote:Is it more less along the lines of 3 times more oxygen gives 3 times more power?

Not quite.

As Jack mused, having an otherwise inert gas in there (without affecting the partial pressure of everything else) does change things.
For example, take the following mix:

1 atm Propane and 5 atm Oxygen (total pressure, 6 atm) - GasEq shows the final pressure as 116 atmospheres.
1 atm Propane, 5 atm Oxygen and 6 atm Nitrogen (same amount of fuel, but total pressure 12 atm) - final pressure, 165 atmospheres.

That's one of the reasons why a viable way of upping hybrid power even after you've reached the vapour pressure of Propane/whatever is to inject inert gas - this doesn't affect the partial pressures of fuel/oxygen, but raises pre-ignition pressures. The effect on the end result is not as effective as being able to add more fuel/oxygen, but still works.

In short, a 5x fuel/oxy mix (about 1 atm pre-ig pressure) is not as powerful as a 5x fuel/air mix (about 5 atm pre-ig pressure.)
Bear in mind, I define mix by the amount of fuel in the chamber, not the final pressure.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 10:17 am

I knew you'd jump in with some numbers, cheers :)

As to my electrolysis setup, it's pretty dismal. Bubble galore but nowhere near the rate I expected, if this thing is going to get off the ground I either need to ramp it up (bigger electrodes, more current etc.) or find myself a small cheap bottle of compressed oxygen.
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Unread postAuthor: Ragnarok » Tue Oct 12, 2010 11:18 am

jackssmirkingrevenge wrote:If this thing is going to get off the ground I either need to ramp it up (bigger electrodes, more current etc.)

It's best to keep the voltage down (I can't find my source to check it, but I think <s>3-4 volts is about the ideal</s> EDIT: Might be as low as 2V or so), so if you want more gas, it means bigger electrodes (which will increase the possible current) and several cells in series.
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Unread postAuthor: Technician1002 » Tue Oct 12, 2010 11:32 am

This more current and the power required is often the factor missed by the free energy from water pseudo scientists. The energy from hydrogen from water does not come free. It takes energy to separate water and then join them back.
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Unread postAuthor: Ragnarok » Tue Oct 12, 2010 12:15 pm

Yes, Tech - but I can't see that being relevant to this particular topic? The same thing is always the case with launchers - you have to put the energy in to fuel/pressurise them - and nobody has claimed otherwise.

We don't have to bring up the laws of thermodynamics every time someone mentions electrolysis.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 1:55 pm

Ragnarok wrote:Yes, Tech - but I can't see that being relevant to this particular topic?


Any excuse to mock the free energy from water pseudo scientists, I agree :)

The numbers aren't very encouraging though, I think I'll give this a go before delving any further into oxygen generation.
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Unread postAuthor: SpudBlaster15 » Tue Oct 12, 2010 2:29 pm

You could always just use bottled oxygen and a regulator. I think I saw that setup on another hybrid recently, but I can't quite recall who made it... :roll:
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Unread postAuthor: saefroch » Tue Oct 12, 2010 6:45 pm

Ragnarok wrote:It's best to keep the voltage down (I can't find my source to check it, but I think 3-4 volts is about the ideal EDIT: Might be as low as 2V or so)

Depends on your electrode material. So far as I know, one of the best is graphite, and even that has very significant decomposition at 3V.

Who ever said anything about "cells"? What about wall outlets (not running at 125V of course, but even a cell phone charger can take that down to 3V)
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 12, 2010 10:58 pm

SpudBlaster15 wrote:I think I saw that setup on another hybrid recently, but I can't quite recall who made it... :roll:


It was you! Silly :)

Of course if I had access to bottled oxygen I wouldn't be fiddling with electrolysis...

saefroch wrote:Who ever said anything about "cells"? What about wall outlets (not running at 125V of course, but even a cell phone charger can take that down to 3V)


*cough* check my diagram *cough*
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Unread postAuthor: BeaverRat » Tue Oct 12, 2010 11:43 pm

Electrolysis starts at around 1.6 volts, but to get any reasonable amount of amp draw, you must have several square inches of electrode surface area, and about 2.4 volts. Any more than that, and the electrodes will deteriorate rapidly, and you will be producing lots of steam along with hydrogen and oxogen due to electrode heat buildup. You also shouldn't run more than 1 watt per 1/2 inch squared of surface area. A couple months ago I had a reliable setup producing 2 Liters per minute of mixed hydrogen and oxygen. It ran on 50 amps, 12 volts, with the voltage spread across 5 plate gaps. If you are interested, I made a quick writeup of how I did it... Note, I refer to the gas as HHO, I know this is completely incorrect, but I did so because it is a recognized term for the product of electrolysis.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 13, 2010 1:11 am

Thanks for the tips :) is there a cheap plentiful source of graphite that doesn't involve me dismembering pencils though? Or another suitable electrode material? Can I go with stainless steel then ethically dispose of the electrolyte in an environmentally friendly manner?
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Unread postAuthor: Insomniac » Wed Oct 13, 2010 2:12 am

Grab some 6V lantern batteries, and prise open the plastic... They usually contain four large zinc carbon cells. The center electrode is graphite in each of these cells, and being zinc carbon cells they are relatively safe and easy to dismantle. ('Heavy duty' batteries are usually Zinc-Carbon... alkalines obviously arn't what you're looking for.)
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