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Liquid Propane Combustion?

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Liquid Propane Combustion?

Unread postAuthor: kjjohn » Tue Jul 27, 2010 7:24 pm

Say you had 1 gram of liquid propane. How much air would be required to ignite 1 gram of liquid propane, and would it release significantly more energy than larger "gaseous" propane combustions? How much air would you need to get the right stoichiometric ratio?
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Unread postAuthor: Technician1002 » Tue Jul 27, 2010 7:35 pm

Propane won't burn without air. It burns after it mixes with air. Liquid only won't ignite until it is mixed. This will provide poor power compared with propane mixed with air.
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Unread postAuthor: kjjohn » Tue Jul 27, 2010 7:39 pm

I don't think you understood my post correctly. :) This would still involve air. I am asking how much air would be required to ignite 1 gram of liquid propane, and if it would provide much more power in a smaller package. Sort of a super-high density hybrid. Of course, you couldn't use liquid air, but that could possibly supplied by a pump. The liquid propane could be stored in a cartridge, then released from the cartridge into the air chamber prior to ignition, eliminating the need for a propane tank.
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Unread postAuthor: ramses » Tue Jul 27, 2010 8:28 pm

oops, sorry. :oops: remove.
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Last edited by ramses on Tue Jul 27, 2010 8:30 pm, edited 1 time in total.
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Unread postAuthor: ramses » Tue Jul 27, 2010 8:28 pm

well, it would flash boil until the partial pressure of propane in the system was equal to the temperature of the gun. You would be nearing a 300x hybrid before it would stay liquid, and even then, a significant portion would vaporize.

With regard to metering by mass:

C3H8 + 5 O2 → 3 CO2 + 4 H2O + heat

so,

Code: Select all
1g               x     1 mol C3H8     x       21% O2      x     24.465 L (@25* C)
44.1 g/mol          5 mol O2                 100% air               1 mol air


edit: fixed formatting.
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Last edited by ramses on Wed Jul 28, 2010 9:23 am, edited 1 time in total.
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Unread postAuthor: ilovefire » Wed Jul 28, 2010 2:02 am

i once had the exact same thought but i was thinking liquid oxygen and propane! i have always wondered if it would work as well
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Unread postAuthor: SpudFarm » Wed Jul 28, 2010 3:31 am

Well, as fas as I know you simply can't liquify propane while you have 86%air mixed in with it.
And if you want to dump liquid propane in to a air chamber and then ignite the mix it would be exactly the same as opening the valve on your propane bottle when fueling a hybrid.

You would need a chamber alot bigger then the propane chamber. Could probably be a pretty good way to fuel a hybrid quickly though.

I'll have to give this some thought.
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Unread postAuthor: kjjohn » Wed Jul 28, 2010 9:16 am

I am not saying that I want the propane to stay liquid. Once it is discharged from the cartridge, it will expand into a gas in the chamber.
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Unread postAuthor: D_Hall » Wed Jul 28, 2010 9:18 am

ilovefire wrote:i once had the exact same thought but i was thinking liquid oxygen and propane! i have always wondered if it would work as well

Congratulations, you'd have a high explosive on your hands and full blown detonation would be virtually assured.

That's *IF* you managed to actually mix the two without spontaneous combustion occuring first.
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Unread postAuthor: D_Hall » Wed Jul 28, 2010 9:19 am

kjjohn wrote:I am not saying that I want the propane to stay liquid. Once it is discharged from the cartridge, it will expand into a gas in the chamber.

Then you're not igniting liquid propane. You're igniting gaseous propane and the answer for your gun is the same as every other propane powered gun on this webpage (hint: when you buy a bottle of propane at the store, it IS liquid inside there).
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Unread postAuthor: kjjohn » Wed Jul 28, 2010 9:50 am

I guess what I'm trying to say, is could you use, say, a small amount of liquid propane in a cartridge, then release it into a chamber precharged with the correct amount of air. I know that a propane tank has liquid propane, but my idea is meant to make fueling quicker, and propane tanks do not discharge a liquid, they discharge a gas, which even at its unregged pressure, is not nearly as dense as the liquid. By injecting a liquid, and allowing it to expand into a gas (which would happen very quickly), you could greatly increase the amount of propane injected into the chamber. It would make high-mix hybrids quicker and easier to fuel, eliminating the need for a meter pipe.
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Unread postAuthor: SpudFarm » Wed Jul 28, 2010 10:40 am

First off, I don't think it will mix that fast. I imagine the pressure of air being much greater then the pressure of the propane. It might boil into gas damn fast (boiling terms) though.

If you don't want a fuel pipe it is another option: Manometric metering.
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Unread postAuthor: SpudBlaster15 » Wed Jul 28, 2010 12:38 pm

kjjohn wrote:I guess what I'm trying to say, is could you use, say, a small amount of liquid propane in a cartridge, then release it into a chamber precharged with the correct amount of air.


Yes, it will work. Will it be effective? I very much doubt it. As a chamber fan will not withstand the conditions within a hybrid chamber, the incoming air charge is responsible for fuel/oxidizer mixing. Simply dumping fuel into a pressurized chamber will achieve very little initial mixing, and it will likely take a significant fraction of an hour for the propane to diffuse and mix with the air.

The best way to achieve effective mixing is to measure the gaseous fuel within a fixed volume, then inject the air through this volume and into the chamber. Such a design was first implemented a few years ago, and it fixed all of the issues people were having with small volume hybrid metering.

SpudFarm wrote:If you don't want a fuel pipe it is another option: Manometric metering.


Manometric metering is great, and likely the best system for high mix fueling, but only if you have a very precise and accurate gauge for measuring fuel pressure. It's very easy to achieve significant errors with the system, especially at low to moderate mixes. At 10x, you're looking at ~3PSI being the difference between a stoichiometric mixture of propane and air, and a mixture that is below propane's LEL.
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Unread postAuthor: SpudFarm » Wed Jul 28, 2010 12:47 pm

My gauge is by no means accurate, but I havent had one single missfire due to the gauge reading wrong pressure. Not even at 3x mixes.

My gauge has been abused by 150psi of air so the needle was at max all the time. I had to jam the mech inside the gauge and twist the needle to the right position and it is still working (:D)

I REALLY suggest to everyone; Use manometric meters!
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Unread postAuthor: jimmy101 » Wed Jul 28, 2010 4:58 pm

SpudFarm wrote:I REALLY suggest to everyone; Use manometric meters!
Or a $2 syringe.
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