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Gen, III 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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Gen, III Hybrid

Unread postAuthor: pbmann123 » Tue Oct 16, 2007 1:10 am

alright guys, i brought this up a year or two ago on spudtech, and i have had some time lately, i just came back from the north, and bought a house, i also have an intown job that is only 40 hours a week, novel thought hey. Anyway, being a machinist and a welder by trade i decided to put my skills intob uilding my idea of a generation 3 hybrid.


The basic principal behind the gen 3 hybrid is that like an normal hybrid you inject fuel, in this case propane, into an atmosphere containing 21 percent oxygen. the difference is that the atmosphere in a gen 3 hybrid is made up of primarily helium, which being lighter than air, will allow for faster flame front propagation, as well as a higher speed of sound allowing the projectile to overcome the restrictions of atmospheric speed of sound.


that being said; the method to accomplish this is that once a projectile is loaded, and the burst disk secured, the chamber is flushed with helium until the air has been displaced. then the propane is injected, followed by oxygen, and the the pressure differential is made up with helium. so after fuel and oxygen have been injected, in the proportions for a 4 times mix, the ambient chamber volume is increased to 58.8 psia.

some of the other factors i have included with this design is the flexibility to allow higher fuel oxygen concentrations and lower fuel oxygen concentrations, with the ability to vary the ambient pressure. the flexibility is due to the fact that i can easily vary the chamber pressure with an inert gas and leave the same relative concentrations of fuel and oxidizer. anyway, i have completed some of the work on the gen 3, and there is still more yet to do, but the basic dimensions are a 2.5 by 12 inch sch 160 steel chamber, high pressure brass gas fittings, singular gas injection port, as well as a max pressure gauge assembly. the ignition is a custom plug driven at 12,000 by a neon sign transformer.


hopefully i will have some more time in the next few days and will date with more specs, and some pictures, but for the time being thats all i have time for.

regards,

Pb
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Unread postAuthor: Novacastrian » Tue Oct 16, 2007 1:30 am

Hey Pb thanks for the informative script.
In the back of my tiny little brain i have always thought that air is the fuel to all things burning, i realise that it is the oxygen that fuels the fire however i always had this stupid idea that all the other gasses would have some appreciable effect on the flamefront. I now understand combustion in an entirely different way because of the way you wrote.
I do not understand why it made my noggin click, but it did!

Your method (or theory as of now) seems like it could give way to a entirely new and rather safe way of projecting spuds at super high velocities due to greater control gained (you would know EXACTLY how much bang to expect).

I can see a super advanced Hybrid coming along here.

Kudos
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Unread postAuthor: BOMBOMBOMB » Tue Oct 16, 2007 2:41 am

Yea go for it!!! this is how technology advances with a smart and skillfull pioneer of destruction :twisted:
Best of luck on this new generation of hybrid aye. Break the abrriers and while your there smash what evers outside it.
Cheers Nato
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Re: Gen, III Hybrid

Unread postAuthor: jimmy101 » Tue Oct 16, 2007 12:28 pm

pbmann123 wrote:The basic principal behind the gen 3 hybrid is that like an normal hybrid you inject fuel, in this case propane, into an atmosphere containing 21 percent oxygen. the difference is that the atmosphere in a gen 3 hybrid is made up of primarily helium, which being lighter than air, will allow for faster flame front propagation...


I'm don't know if the flame front will propagate faster in a helium/oxy environment versus a air. The flame front "propagates" but the gases really do not move anywhere near as fast. Indeed, they probably don't move at all until the projectile starts to move. So, I would think that changing to a lighter co-gas probably will have a pretty minor affect on the flame front speed.

Is there any evidence from say gasoline engine or rocket engine design that a light co-gas like helium increases the burn rate? I can see there being an affect based on the difference in heat capacity between nitrogen and helium but off hand can't guess which gas would be better.

To boost the speed of the flame front you want it to be a turbulent front and not a laminar front. The easiest way to do that is to have a chamber fan running during the firing.

I'm not even sure that the helium will help all that much in how fast the gases can move through the gun because of the speed of sound restriction. The gases in a standard 1x combustion are what ~2600K? According to GasEq the speed of sound in a 1X propane + air mixture after combustion is 3250 FPS. So the speed of sound really doesn't affect the movement of the gases in a combustion gun all that much, at least, not in terms of getting the projectile to exit the barrel at >1100 FPS.

But hey, a kick-ass hybrid is always a nice thing to see.
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Unread postAuthor: benstern » Tue Oct 16, 2007 3:55 pm

Why not just skip the whole helium and make it all oxygen?
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Unread postAuthor: pbmann123 » Tue Oct 16, 2007 8:24 pm

well first off thanks for the comments and support, hopefully it turns out well.

In response to jimmy i do not know as an absolute fact that helium will increase the flame front propagation, but i do think the the smaller atomic radius of helium versus nitrogen will allow the gasses to " slip and slip" easier, and that its lower thermal constant will allow it heat up faster and transfer the heat. also having a smaller atomic radius will allow the molecules of propane and oxygen to be closer. Although my high school chemistry tells me that because one mole of nitrogen and one mole of helium have the same volume at the same pressure that there will just be more " heliums" between the propane and the oxygen. as far as no gas movement before the burst disk goes, it seems to me that as the flame front which originates in the back will create a localized high pressure at and behind the female front which is going to push gas forward. And this seems to follow that you can trigger a ddt with a very long chamber, because as the flame front pushes forward it will compress the gas ahead of it. although i am by no means an expert it seems logical to me.


AS far as making the entire chamber oxygen i will be able to experiment with different pressures and mixes with this design and inherent tot he design is the ability to be vastly adaptable. we will be able to see the effects of mix / pressure.
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Unread postAuthor: HaiThar » Tue Oct 16, 2007 8:30 pm

pbmann123 wrote:In response to jimmy i do not know as an absolute fact that helium will increase the flame front propagation, but i do think the the smaller atomic radius of helium versus nitrogen will allow the gasses to " slip and slip" easier...


Spudguns on the atomic level?

:shock:

Will it have that great of an effect? The investment may not be worth the return...
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Unread postAuthor: benstern » Tue Oct 16, 2007 9:03 pm

HaiThar wrote:Spudguns on the atomic level?

Will it have that great of an effect? The investment may not be worth the return...


Go back to school! Atomic radius refers to the size of the atom thus atomic.
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Unread postAuthor: Lentamentalisk » Tue Oct 16, 2007 9:31 pm

benstern wrote:Why not just skip the whole helium and make it all oxygen?


Because then you get DDT, as well as a bunch of metal shrapnel embedded in the back of your skull...
Plus, your spudgun ends up in many pieces, putting you hundreds of dollars down. That in addition to the cost of your funeral is just too much for most people to afford.
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Unread postAuthor: pbmann123 » Tue Oct 16, 2007 9:58 pm

so i was doing some thinking, and i realizer how complicated gen three terminology is going to be because we no longer have the atmosphere as a standard. So for the time being we will only consider the 4.23% propane atmosphere mixture, and the atmosphere will have the normal 21 percent oxygen. this is just currently, because we could get side tracked on this mixture and this , get confused with amount of fuel or the chamber pressure in relation to atmospheres. so for the time being only the 4.23 % fuel and 21 percent oxygen atmosphere will be considered. Period.

now one other thing i would like the address is wether to use a oxygen meter, or do the calculations for straight pressure increase. so once chamber is flushed and at atmospheric pressure, propane is added, and then either meter in oxygen, which presents its own complications or just add propane until such a chamber pressure is reached. Now the later seems the better option to me but i have no idea how to do the math to get from 21 percent to a specific psi. Although i did realize that no matter what the chamber volume, the psi for 21 percent will be a constant. so just use a hypothetical chamber of 1000 cui, or cm3 or what ever number you would like as long as the psi works out its peachy. So if some one could help out the less mathematically inclined i would much appreciate it.

so can someone please figure out the gen. III constant.

some final issues have we ( the spudding community) figured out the optimal c:b for a hybrid, did we leave it off at each atm acts as another chamber volume in a standard combustion or did we figure out an optimal ratio yet?


and finally i will go take some pics now and post them in an edit.

so pictures, first of an overhead view of the manifold, with the 400 psi glycerine filled gauger, chech valve and release valve.

Image

secondly a side view of the manifold.

Image

thirdly a view of the three gas inlets, the top being helium the bottom left oxygen and the bottom right propane, the meters and regulators havent been attatched yet.

Image

and finaly an entire overview of the chamber and manifold, with a 6 inch rule in the foreground for scale.

Image


regards,

Pb
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Unread postAuthor: spanerman » Wed Oct 17, 2007 3:35 pm

looking VERY nice...keep us posted :D :shock:
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Unread postAuthor: pbmann123 » Wed Oct 17, 2007 5:55 pm

so todays update, i came home from work nd built the propane meter, and plumbed the oxygen in. so i really need some one to help me out with what psi of oxygen i need to inject into a inert chamber to give me 21 percent oxygen.

other than that i painted a bunch of the manifold last night, but its a secret until its done now, also praxair called me and my helium tank reg and other stuff will be in two weeks from today.

regards,

Pb
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Unread postAuthor: Novacastrian » Wed Oct 17, 2007 9:34 pm

I am also Mathematicaly challenged, so i can't help you there, but i know who could. PM JacksSmirkingRevenge, i'm sure he would be pleased to help, aint that right JSR?
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Unread postAuthor: DYI » Thu Oct 18, 2007 4:25 pm

To get it exact, you would need to have the helium at 79% atmospheric pressure before the O2 injection, which probably isn't practical.

When you add the O2, the pressure in the chamber will raise slightly.
Say you have a 10ci chamber, just for the sake of easy calculations. There will be 10 ci of helium in the chamber before O2 is injected.
Since this 10 ci will make up ~79% of gas in the chamber after the O2 injection, the amount of gas in the chamber after the O2 is added would take up ~12.658 ci at 0 psig.
Therefore, you should add 2.658 ci of O2 to the chamber. (I think)
Because 12.658 ci of gas is forced into 21% less space than it would usually take up, the internal pressure of the chamber after O2 injection would be ~17.787 psia, or 3.787 psig. (I think)

When multiplied by say, 4, for a 4x mix, the chamber pressure after O2 and helium injection and before propane injection would be 17.787x4=71.148 psia, or 56.448 psig. (I think)

At a 4x mix, 10.632 ci of O2 would be present in the chamber, and since propane burns best at about 19% in pure O2, you would need 2.94 psi of propane in the chamber as well. This raises the pressure from 71.787 psia to 74.727 psia, or 60.027 psig. (I think)

As you can see, the maths for a GenIII hybrid are somewhat complex. All of these calculations could probably be done much faster, but I don't know how, so I took a roundabout method that can be devised from logic alone. These calcs assume an atmospheric pressure of 14.7 psia.

In short, the answers are: A "1x mix" in a genIII is actually about 3.787psig, so each extra atmosphere of helium would require the addition of 3.787 psia of oxygen to get a 21% oxy mixture.

For each extra atmosphere, you will need .735 psi more propane, as opposed to .6psi more propane in a normal hybrid, due to the slightly higher initial pressures created due to the oxygen injection.

Keep in mind that these numbers may very well be wrong. I would advise PMing Spudblaster15 for a definitive answer, but these numbers seem close.
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Unread postAuthor: pbmann123 » Thu Oct 18, 2007 7:04 pm

there is a problem with that, i need to inject the oxygen first, because the bernzomatic was only kind enough to give me a reg that tops out at 1`5 psi. also i do have a propane meter that injects one atm's worth of propane. so i get the mix that is need for a normal hybrid. this is so we cant say a gen three is more powerful per atm only because of the extra fuel, and also so i can fire the thing as a normal hybrid because i don't want to always be buying helium.


as it stands today i started the stand and the ignition, i also went through and leak proofed the entire cannon, i has been holding 150 psi for almost 4 hours now and no variation in pressure is observable. also sop water test shows no bubbles on any of the joints.

so i just need to wait for the helium kit to arrive, finish the ignition, and stand and build a barrel, i am thinking copper and AA sized :P. I also need a definitive number for the o2 injection.

regards,

Pb
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