Hydrogen and Airguns

[rsterne]

There has been some discussion on this Forum about the possibility of using compressed Hydrogen (instead of Helium) as a propellant in PCPs.... Intuitively (thinking of the Hindenberg) I think this is a bad idea, so I decided to look for a couple of UTube videos to demonstrate how combustible / explosive it is.... Check these out....

First, a balloon filled with Hydrogen....



Secondly, bubbles of Hydrogen/Oxygen mix being lit with a match....



Third, an egg filled with Hydrogen, hole in the top, lit with a match....

http://www.thenakedscientists.com/HTML/content/kitchenscience/garage-science/exp/exploding-eggs-burning-hydorgen/

All of these videos use quantities of Hydrogen that might be typical of the volume of Hydrogen used for a shot with a PCP or a spill occuring during filling or venting.... We all know that three things are required for combustion.... Fuel, Oxygen, and ignition.... If we use Air, Nitrogen, CO2, Argon, or Helium, we are not providing a fuel.... If we use Hydrogen, we are.... There is oxygen present in the air we breath.... all you need is a source of ignition and you could lose your eyebrows or worse.... No question that with proper purging and careful handling Hydrogen COULD be used.... Is it a good idea?.... I don't think so....

Why would anyone want to use it?.... In theory, the limiting factor for velocity in a airgun using expanding air is the RMS speed of the molecules in the gas, and that depends on the molecular (or atomic) weight of the gas.... Hydrogen is 1, Helium is 4, Nitrogen is 28, Air (a mix) is 29, Argon is 40, and CO2 is 44.... Those result in the following "speed limits"....

Hydrogen: 8887 fps
Helium: 4444 fps
Nitrogen: 1680 fps
Air: 1650 fps
Argon: 1405 fps
CO2: 1340 fps

As we know, air works darned well up to over 1000 fps, but the performance seems to drop off as we approach the speed of sound (1130 fps).... If we make the same assumption about Helium, the speed of sound is 3190 fps, so we should be able to have reasonable efficiency up to 2500-3000 fps.... While Hydrogen might double that again, you have to ask yourself if there is really any reason to take the chance?.... Do you have the skills to build an airgun that will shoot over 3000 fps to take advantage of it?.... My personal opinion is that only air and inert gases should be considered for use in PCPs.... Based on performance and/or availablity, the only two that make sense to me are Nitrogen (available from Welding supplies) and Helium (commonly used for balloons).... I think playing with Hydrogen is, quite literally, playing with fire....

Bob

[amb5500c]

Good post Mr. Bob. Stick with whats tried and true. And remember folks: Even with whats tried and true, there have been several extremely dangerous and potentially fatal mishaps. Mostly due to the lack of thorough education of the user, about dealing with pressurized air etc. and vessels.
Richard

[Brewerja]

i agree, i tried helium in my mrod once and saw about 23% increase in velocity but, the helium gas molecules being much smaller then oxygen/nitrogen mix (air) leaked out of my pressure cylinder in the rife. I know that hydrogen is the smallest and most simple molecule in existance so, i dont know how we would be able to keep the pressure behind those orings. plus, i dont want an explosive gas in my gun! id be afraid to go near anything electrical until it was completely discharged of pressure. helium was fun to try because its inert but, im not messing with boom gas!

[PakProtector]

The usual cause of death for  German Zeppelin was a British Pilot spitting .303 incendiary at them. Eckner never had any issues...

The stoic hydrogen explosion is interesting, but not germane; nobody is suggesting combining it with o-2. I'll bet heavily that it would have been anticlimactic had he just used air...
cheers,
Douglas

[ezman604]

http://www.ehow.com/about_5393335_hydrogen-fuel-cell-dangers.html

Hydrogen is a fuel. No place in a PCP airgun application for it to be used safely.
SAFE & Happy Shooting!!!!
Dave
 

[MustangMike]

i always wondered what helium would do performance wise in a 25cal shooting a heavy pellet/slug or in a big bore.. seems like it would provide more power if the accuracy can stay good with the extra power..

[williesurvive]

The hydrogen would ignite before the pellet was out of the barrel. Based on the work of Dr. Dryer

[Dead nuts dog]

That was fun to watch

[PakProtector]

The hydrogen would ignite before the pellet was out of the barrel. Based on the work of Dr. Dryer

With what oxidizer? There is only the air in the transfer port. And if you've taken a shot, it will be high in hydrogen concentration.
cheers,
Douglas

[Cal]

And those crazy fire arms guys are using "GUN POWDER"!

 That stuff could blow up!

But the first video reminded me of an antic that I ahh ....err.  participated in.

Two balloons tied together,  One was a He party balloon, and the other was "somehow" filled with a "hard flame mix" of oxy/acetylene.

We rigged a AA battery to a fine wire on a cheap mechanical watch, Timed at 5 min.  Then set the whole affair free to drift in the breeze.

We counted down the seconds.  five, four, three, two, one, 

Then there was a very  big sound,  we were stunned and awed.
This did take place in somewhat of a valley in Northern New Hampshire, and I'm sure the reverberation added to the impact of the event.

But it was a VERY loud sound.

I hear that Acetylene is just south of TNT on the Richter scale.

[Cal]

Would Di-hydrogen monoxide be OK,  I hear it was used a long time ago to power all sorts of things.   I can get it from the local chemical supply,  but I'm worried about the mixture of both Hydrogen AND oxygen.

cheers

[williesurvive]

http://www.princeton.edu/mae/people/faculty/dryer/homepage/research/hydrogen-fire-safety/movies/Dryer_et_al_CST_179_2007.pdf   Maybe I miss understood this paper it has been over 30 years since college. This never was my area of interest.

[dukemeister]

Would Di-hydrogen monoxide be OK,  I've hear it was used a long time ago to power all sorts of things.   I can get it from the local chemical supply,  but I'm worried about the mixture of both Hydrogen AND oxygen.

cheers

I heard it's not good for the internal components of rifle and charging equipment. Causes corrosion when the hydrogen and oxygen dissociate setting up galvanic action between dissimilar metals, and oxygen concentration cells on the ferrous metal parts.

[Rescue35]

You also need to consider Hydrogen brittlization of any container used to store H. Since Hydrogen is so small it finds a way out through just about everything...including "solid" metal. As it does, H deteriorates it. Causing it to weaken.

[Bent]

Would Di-hydrogen monoxide be OK,  I hear it was used a long time ago to power all sorts of things.   I can get it from the local chemical supply,  but I'm worried about the mixture of both Hydrogen AND oxygen.

cheers

You can buy it in bottles at the store, with and without CO2.... 


H2O..... ? is Water

[Rescue35]

Would Di-hydrogen monoxide be OK,  I hear it was used a long time ago to power all sorts of things.   I can get it from the local chemical supply,  but I'm worried about the mixture of both Hydrogen AND oxygen.

cheers

You can buy it in bottles at the store, with and without CO2.... 


H2O..... ? is Water

Check out this link to inform yourself of the dangers "DHMO". http://www.dhmo.org/dihydrogen-monoxide/

[Bent]

Check out this link to inform yourself of the dangers "DHMO". http://www.dhmo.org/dihydrogen-monoxide/

ROFL... 

[Rescue35]

I hope you went to the main page also. They have a store too, I so need this tshirt.



/threadjack

I would like to see the difference in real world performance of these various gases in a test rig with the only variable being the gases themselves. It would be interesting academically. I do not see hydrogen being practical as a regular use propellant due to the safety, containment, and cost issues. How much more would hydrogen cost versus the same amount of HPA?

[aack73]

throw in some hops, yeast, malt etc. and i'll ingest it, as a death defying act in an effort to expose this for what it really is.

[amb5500c]

Stick with the inerts people. There's absolutely no sense in experimenting with potentially fatal gasses under high pressure. There is plenty enough danger to go around, using the accepted and reccommended methods. Do NOT underestimate the dangers of just plain old air, when its pressurized. This can not be stressed enough.
Richard