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The highest possible mix for a 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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The highest possible mix for a hybrid?

15x
1
8%
25x
0
No votes
50x
0
No votes
75x
0
No votes
100x
0
No votes
100+
11
92%
 
Total votes : 12
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The highest possible mix for a hybrid?

Unread postAuthor: Larda » Thu Jul 24, 2008 4:51 pm

How high mix hybrids do you think its possible to build?
Can you go above, lets say, 15x, 25x, 50x 75x, 100x or even higher?
To clarify i am talking about Air-Propane, not Oxy-Propane.
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Unread postAuthor: jimmy101 » Thu Jul 24, 2008 5:24 pm

This has been asked and answered before.

The limitation is the liquifaction pressure of the mixture. Propane liquifies at a fairly low pressure. What's the pressure in a propane tank at 70F? 150 PSI or something like that?

So you can't get anywhere near 100X.
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Unread postAuthor: BC Pneumatics » Thu Jul 24, 2008 5:32 pm

The highest mix you can achieve depends on the temperature.
At 70*F the vapor pressure of propane is 110psi. This means with a partial pressure of roughly 4%, you are limited to 2800psi, or around 190x, before any extra propane turns to liquid.
Of course building a cannon that can hold 2800psi is a bit of a challenge in and of itself. Trying to ignite a mixture that is at that pressure is something else entirely. It is 'possible' to build a launcher to contain this, so there's your answer, but I wouldn't hold me breath on seeing one.
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Unread postAuthor: SpudFarm » Thu Jul 24, 2008 7:22 pm

i can correct jimmy:D

on 100x you want 4.3bar of propane and that is totally doable.
the limit will be 200x then the pressure is 8.6 bar and that is also doable since.....
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Unread postAuthor: BC Pneumatics » Thu Jul 24, 2008 7:41 pm

SpudFarm,
Almost feels good in a schadenfreude sort of way, eh? :wink: :lol:

Of course one can see from both SpudFarm's post and mine as well that the ambient temperature is the big factor here. While a person in one part of the world may be limited to 120x, another could achieve twice that just because it's a warm day.

But, it doesn't matter if no one is willing to take up the geometric increase in cost that is associated with an arithmetic increase in performance.
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Unread postAuthor: SpudFarm » Thu Jul 24, 2008 8:00 pm

who knows?someone may feel like setting a record someday BC, if i har a lathe and a huge tungsten carabide steel bar and the cutters needed i would have found the limit :D

and yes it is pretty good to correct the smartesy guy on the smartest website ever! he will do comeback and say [jamie hyneman voice] oh i meant 200x "typo" [/jamie hyneman voice]
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Unread postAuthor: jimmy101 » Thu Jul 24, 2008 9:13 pm

I stand corrected. BC and SPudFarm are correct.

I forget a "minor" factor of ~25x. :oops:
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Unread postAuthor: SpudMonster » Fri Jul 25, 2008 3:51 am

And for more fun, we simply go to Natural Gas instead of propane. I have no idea what the vapor pressure is, but CNG is stored at about 2900-3200 PSI, so with a stoichometric ratio of about 5%, we could have 4,353x hybrids (hypothetically). And if we assume that Natural Gas behaves similarly to propane (minus 20 percent because of its lower energy content) when combusted, given that an atmospheric propane mixture produces a maximum of 100 PSI (and 4x mixtures produce approximately 400 PSI with proper discs) then a post-combustion maximum pressure of almost 350,000 PSI would be possible.
I probably am wrong, but it's still fun to fantasize about.
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Last edited by SpudMonster on Fri Jul 25, 2008 4:00 am, edited 1 time in total.
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Unread postAuthor: ALIHISGREAT » Fri Jul 25, 2008 3:56 am

just out of a matter of interest, what kind of pressures are produced in BIG gun barrels, like tank gun barrels, maybe the military should forget solid fuel in favour of a high pressure mix of gases?
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Unread postAuthor: DYI » Fri Jul 25, 2008 8:19 am

I believe that some tank guns can reach as high as 90 kpsi barrel pressure. Nitrocellulose has a maximum combustion pressure of well over 300 kpsi. The really high pressure mixes are to be had with oxy/hydrogen though. If I remember correctly, neither of those gases can liquefy at room temperature (they will obviously become a supercritical fluid though, and it would be interesting to see how those behave in a hybrid), so the highest attainable mix is really whatever your hardware can withstand.

maybe the military should forget solid fuel in favour of a high pressure mix of gases?


A good rule of thumb: If you come up with a good idea, chances are that it's already been thought of by someone else, and probably already built. In this case, Utron's CLGG takes the honors, using a light gas mix (either CH<sub>4</sub> or H<sub>2</sub> burned in what is presumably pure oxygen, they don't really specify), to fire projectiles out of a 155mm bore at speeds in excess of 4km/s. I read something about it being able to hit a 5 metre square target at 100 miles as well.
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Unread postAuthor: paaiyan » Fri Jul 25, 2008 8:30 am

SpudMonster wrote:And for more fun, we simply go to Natural Gas instead of propane. I have no idea what the vapor pressure is, but CNG is stored at about 2900-3200 PSI, so with a stoichometric ratio of about 5%, we could have 4,353x hybrids (hypothetically). And if we assume that Natural Gas behaves similarly to propane (minus 20 percent because of its lower energy content) when combusted, given that an atmospheric propane mixture produces a maximum of 100 PSI (and 4x mixtures produce approximately 400 PSI with proper discs) then a post-combustion maximum pressure of almost 350,000 PSI would be possible.
I probably am wrong, but it's still fun to fantasize about.


What exactly would one use for a burst disc on a cannon like that, 1/4" steel plate?
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Unread postAuthor: DYI » Fri Jul 25, 2008 8:47 am

What exactly would one use for a burst disc on a cannon like that, 1/4" steel plate?


Depends on the bore. D_Hall is using 1/4" plate for burst disks in his Pipe Dream, and they'll be bursting at well under 100 psi, if I remember correctly.
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Unread postAuthor: SpudFarm » Fri Jul 25, 2008 9:10 am

but if you want to go onto a like 1000x isnt it just to messure and calculate the amount of liquid propane needed for that shot and then have a flow messure instrument like they use on the fuel line on cars to find out how much fuel it use, so you can messure it out? it will make sence to me that it turns to gas when it gets 999bars of air on it and it is just 4.2% of gas in there again :?

heck that was har to explain to me
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