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butane vs propane

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: kcajblue » Wed Feb 14, 2007 12:57 am

chaos wrote:
Mic Whitey wrote:butane is much better than propane. it's not hard to get the mixture right at all. I made tool that gives me control to give two shots of butane for 4" gun and 3", so ha


mate please i beg you, i have spent hours in the shed "trying" to make something to measure it please post plans. i am sure if this works good many people will be help by this also
thanks mate.

peace
chaos
paslode fuel cells have their own metering thing that only allow a certain amount per press.
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Unread postAuthor: chaos » Wed Feb 14, 2007 5:38 am

BC Pneumatics wrote:chaos, butane is packaged by weight, so it would be incredibly easy to find out how much is in it. all you have to do is look at the Can



mate i mean how measure how much comes out
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Unread postAuthor: BC Pneumatics » Wed Feb 14, 2007 8:28 am

Well, you could use the same system we do for propane, or use a liquid meter. As far as 'guessing', it wont be terribly accurate. ;)
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Unread postAuthor: kcajblue » Wed Feb 14, 2007 8:19 pm

chaos wrote:mate i mean how measure how much comes out
like i said. you can buy paslode fuel cells. they have their own meteting device.
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Unread postAuthor: LGM » Wed Feb 14, 2007 8:44 pm

In my experience with minis, MAPP is more powerfull than butane.

What is the liquefaction pressure of MAPP gas?
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Last edited by LGM on Sat Feb 17, 2007 10:00 pm, edited 1 time in total.

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Unread postAuthor: willarddaniels » Thu Feb 15, 2007 1:56 am

Liquification pressures: @ 70*F
Butane: 30 psi ***be sure to meter with a gauge, don't use with hybrids
Propane: 125 psi ***BEST
MAPP: 120 psi

Explosive limits in air:
Butane: 1.9-8.5% ***BEST
Propane: 2.2-9.5% ***4% is optimal
MAPP: 3.4-10.8%

Flame Temp in Air & Oxygen: (*F)
Butane: 3200 & 4925
Propane: 3450 & 4579 ***BEST for the money
MAPP: 3650 & 5301

Burning Velocity (ft/sec) - THIS IS A CRITIAL NUMBER
Butane: 11.0
Propane: 12.2
MAPP: 15.4 ***QUICKEST combustion time, fastest acceleration

Heating values, primary combustion: (BTU/Ft^3)
Butane: 315
Propane: 255 ***BEST for your chamber fan and PVC housing
MAPP: 517

You can easily find the numbers for acetylene as well, but never use the stuff with your cannons- you will die, it is too unpredictable.

Looks like MAPP is the best performer, but with propane's lower cost and lower heating properties, it seems obvious why it is the most popular (did I mention that refills are cheap?)

But ... draw your own conclusions.
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Unread postAuthor: BC Pneumatics » Thu Feb 15, 2007 2:59 pm

^^^^^^^^^^^^^^^^^^^^^^^^^^
First example of a good post I have seen
by someone with less that 100 posts in a
LONG while.

Great info Willard.

(Also, remember that the flame front will accelerate much higher than the burning velocity)
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Unread postAuthor: chaos » Fri Feb 16, 2007 1:47 am

willarddaniels wrote:Liquification pressures: @ 70*F
Butane: 30 psi ***be sure to meter with a gauge, don't use with hybrids
Propane: 125 psi ***BEST
MAPP: 120 psi

Explosive limits in air:
Butane: 1.9-8.5% ***BEST
Propane: 2.2-9.5% ***4% is optimal
MAPP: 3.4-10.8%

Flame Temp in Air & Oxygen: (*F)
Butane: 3200 & 4925
Propane: 3450 & 4579 ***BEST for the money
MAPP: 3650 & 5301

Burning Velocity (ft/sec) - THIS IS A CRITIAL NUMBER
Butane: 11.0
Propane: 12.2
MAPP: 15.4 ***QUICKEST combustion time, fastest acceleration

Heating values, primary combustion: (BTU/Ft^3)
Butane: 315
Propane: 255 ***BEST for your chamber fan and PVC housing
MAPP: 517

You can easily find the numbers for acetylene as well, but never use the stuff with your cannons- you will die, it is too unpredictable.

Looks like MAPP is the best performer, but with propane's lower cost and lower heating properties, it seems obvious why it is the most popular (did I mention that refills are cheap?)

But ... draw your own conclusions.


ok with the bit about acetylene what do you mean by "unpredictable" i ask this because this is my next thought of an upgrade and also because i have a stainless steel gun therefor it will not melt.

peace
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Unread postAuthor: BC Pneumatics » Fri Feb 16, 2007 8:54 am

I think he means more along the lines of 'unstable'.
Spontaneous combustion comes to mind. Also, remember that even in a steel cannon, it isn't necessarily safe. For the same reason that flash powder can't be used in a firearm, or gun powder in a (traditional) cannon, we should be weary of acetylene. It has been used with success, but that doesn't make it 'safe'.
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Unread postAuthor: Pete Zaria » Fri Feb 16, 2007 12:25 pm

Compression
Acetylene gas is highly unstable, and can explode readily if it is compressed. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (roughly 14.5psi) as a gas or when in liquid or solid form, so it is shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with porous filling, which renders it safe to transport and use.
- Wikipedia

Layman's terms: Acetylene will literally self-detonate when compressed which makes it very difficult and unsafe to store. In canisters (or tanks) it's stored dissolved in cotton or other filler soaked in acetone to keep it stable.
Acetylene is also dangerous because of it's huge flammable range; any mixture between 3% and 82% acetylene can be ignited. The ignition temperature is also reasonably low at 335C.

As BC already pointed out, the flame front in acetylene (Especially in hybrid mixtures) can exceed the local speed of sound (making acetylene's combustion process a "detonation" rather than a combustion). This produces a huge pressure spike which will obliterate all but the very strongest plastic pipe (I've heard of people using acetylene in 2" sch120, but I still think it's dumb to use in anything but welded metal pipe).

Additionally, acetylene is also very toxic to breathe.

If I was going to build an acetylene fueled cannon, it would have a small (2" x 12" max) all-steel chamber. I'd use milkjug burst disks, and pressurize the acetylene with compressed air until it self-detonated. It would be STRICTLY remote fired, at least for the first ~50 shots. It'd be a lot of fun though.

Peace,
Pete Zaria.
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Unread postAuthor: plumpthumb » Fri Feb 16, 2007 12:41 pm

I use propane in one of my combustions coupled with a stungun/sparkstrip
for ignition and a fan to mix the air with the gas. All I can say is it gives one solid kick and sends the projectile far out of sight. I have used butane in
other applications and it is passable but can't match propane in my estimation.
Only my experience and opinion.
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Unread postAuthor: LGM » Fri Feb 16, 2007 5:17 pm

Thanks for the numbers willard, I want to use MAPP in a hybrid and wanted to see how high I could take it before it condensed.

For the acetylene, if shocks set it off, could an acetylene cannon be triggered by a tube set off to the side with a spring in it like in some air guns, and have a small opening into the chamber? Then it would compress the acetylene to above it's instability pressure and give it a shock.
||-----------plunger
| || |-----------tube
|----|__________________________________________ -----chamber wall
| |
-- -- ----------------small opening
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Unread postAuthor: frankrede » Fri Feb 16, 2007 7:30 pm

You would have to have a pretty durable setup for that.
I imagine the shock could blow your piston to pieces.
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Unread postAuthor: willarddaniels » Fri Feb 16, 2007 10:00 pm

For the acetylene, if shocks set it off, could an acetylene cannon be triggered by a tube set off to the side with a spring in it like in some air guns, and have a small opening into the chamber? Then it would compress the acetylene to above it's instability pressure and give it a shock.

In theory, yes. However, your combustion chamber would be considerably weaker with that trigger mechanism and as frankrede stated, it could very possibly destroy or shoot off your spring/piston housing.
Solid/seamless chambers that are welded by a professional with high grade stainless, aluminum, or steel would work with acetylene. With the small but respectful amount of experience I have with it, I would still not be comfortable forcing a detonation: planned, or purposely using the unstable properties of the gas to produce the desired effect.

I know, use the hybrid threads for this, but it is applicable here as well:
For my first hybrid ...I currently have a machinist friend constructing a chamber from aircraft-grade aluminum to the measurements: 8"OD, 6"ID with a 2" thick threaded cap on the butt end and a 6-2.5"ID reducer that will be threaded on the business end and then welded. He is also making a custom union for the burst disks. This all costs a bit of monies, so it will be probably a year before it is ready to add components and barrel. I would feel secure that this would be sufficient to hold an acetylene detonation, but I doubt that I will try it. I plan on using a MAPP and small oxygen mix. I just like to over-build things.

Point being: Acetylene is unstable and I caution anyone who is thinking about using it to look at their fingers and other extremities, feel their heartbeat inside them and then rethink their plans.
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