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Stoichiometric's (A.K.A. Fuel/Air Ratio)

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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Stoichiometric's (A.K.A. Fuel/Air Ratio)

Unread postAuthor: khepera1997 » Wed Feb 17, 2010 10:56 pm

I am in the Process of Building a Spud Gun and iv Got Every Thing Down But The Stoichiometric's. (A.K.A. Fuel/Air Ratio)

Number One:I Can Calculate the Stoichiometric's But When i Do i Have the Answers in Volume i Need Some Thing in P.S.I. i Mean How do i use Volume as an Answers Ane way.

Number Tow:What Do People Mean by 1x 2x 3x ext.
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Unread postAuthor: McCoytheGreater » Wed Feb 17, 2010 11:50 pm

Check out the spudwiki.

Burnt Latke has helpful calculators.

The Hybrid Cannon Discussion board has all the answers on 1x 2x and 3x.
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Unread postAuthor: Insomniac » Wed Feb 17, 2010 11:56 pm

Well, firstly you need to work out the volume of the meter pipe is, and then you need to figure out what pressure you will need in that volume to give the correct voume of gas at atmospheric pressure. I've never done this so I don't know the math off the top of my head, but I doubt it's too tricky. It'll probably be easy to find in either the Wiki or the Burnt Latke site.

By 1x, 2x, 3x people are reffering to the 'mix' used in hybrid guns. Hybrid guns pre-pressurize their fuel/air mixture prior to firing to increase the total energy that can be obtained from a given chamber size. The number simply refers to the pre-ignition pressure in BAR. So a 1x mix is 1 times atmospheric pressure (about 14.7 psi), and this is the pressure at which a regular combustion operates (it would show 0psi on a normal pressure guage as these usually measure the difference between normal atmospheric pressure and what they're connected to, and as normal atmospheric pressure is 14.7psi then there is no difference).

A 2x mix has a pre-ignition pressure of 2 BAR etc. Some hybrids go all the way up into and beyond the 200x, or 200 BAR range.
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Unread postAuthor: MrCrowley » Thu Feb 18, 2010 3:41 am

To be honest, I would recommend you do more research if you don't understand what is meant by 1x, 2x and 3x, let alone how to calculate the required fuel pressure. Good thing about hybrids is that they don't work unless you know what you're doing, the bad thing is that if someone tells you how they work and you are unaware of the dangers involved you could cause some serious damage/harm.

Apart from that, check the hybrid discussion sections, the Spudwiki and even the showcase sections.
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Unread postAuthor: rcman50166 » Thu Feb 18, 2010 8:40 am

Well as long as this thread is here. Could anyone tell me the stoichiometric ratio for iso-octane? It's chemical composition is C<sub>8</sub>H<sub>18</sub>. Would that make the ratio 11.5 to one?
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Unread postAuthor: jimmy101 » Thu Feb 18, 2010 3:16 pm

rcman50166 wrote:Well as long as this thread is here. Could anyone tell me the stoichiometric ratio for iso-octane? It's chemical composition is C<sub>8</sub>H<sub>18</sub>. Would that make the ratio 11.5 to one?

2 C<sub>8</sub>H<sub>18</sub> + 25 O<sub>2</sub> = 16 CO<sub>2</sub> + 18 H<sub>2</sub>O

So for each 25 volumes of O<sub>2</sub> you need 2 volumes of C<sub>8</sub>H<sub>18</sub>.

Air is about 20% O<sub>2</sub> so you need (0.2)(2/25) = 0.016, which is 1.6% by volume. That's additive. I believe for displacive it would be 1.57%
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Unread postAuthor: rcman50166 » Thu Feb 18, 2010 3:55 pm

So on an O<sub>2</sub> sensor, I would be looking for a number ideally around 12.5? I just want to be sure. I'm going to be fine tuning an engine and need that number.
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