MAPP//PRO Question

[MrPed]

Does anyone on the forum have experience with MAPP//PRO, it is different than MAPP supposedly it is propylene. Also, does anyone know the fuel:air ratio for MAPP//PRO, or the percentage of MAPP//PRO needed for optimum performance? Here is a picture of it:


Thanks in advance!

[deathbyDWV]

I'm not completely sure because i mostly do pneumatics but i think it's the same as propane. The only difference is that it burns faster. That means MOAR POWER!!! I'm not sure what the difference of regular and pro is. Sorry I hope this helps.

[MrPed]

Well, what you told me, I already knew but still thanks for trying to help! :toothy7:

[spudtyrrant]

map/pro is 99.5% propylene and .5% propane so combustion is listed to be the same as propylene which is between 5% and 9% with the optimum mixture being almost exactly 6% i haven't used it in spudguns before, but it is a form of propane and should have similar performance although it does burn hotter so i am not sure how good performance will be.

[MrPed]

THANK YOU SO MUCH!!!
Btw, why would it burning hotter not be as good for performance?

[spudtyrrant]

well hotter means faster i didn't say necessarily not as good i just said i don't know.

[MrPed]

Ooooo, gotcha nice. :thumbleft:

[hi]

Ive used mapp gas. it doesn't give that much of a difference. maybe a 10% power difference, but it costs a lot more.

[Technician1002]

As far as the air mix, it's almost the same as Propane. As with any combustion cannon, start at the calculated mix and then due to pipe size, valve and pipe nipple dead spaces and other factors, adjust slightly to find the sweet spot.

[spudnutbutthut]

what is dead space?

[Technician1002]

what is dead space?

Space between the meter pipe and chamber.. It may contain air, combustion gas or fuel.. When the metered propane or gas is delivered, some remains in this space instead of entering the chamber. This throws off the calculated mix, so experimentation is used in several shots to get the metering tuned to your plumbing.

[Ragnarok]

Ive used mapp gas. it doesn't give that much of a difference. maybe a 10% power difference, but it costs a lot more.

Your maths is disregarding something important.

Bear in mind the cost of your gas.
It costs me about £8 for a 400 gram propane cylinder, which would last 1100 shots in a 24" long 4" diameter chamber.
We'll call it 1000 to compensate for possible problems. 0.8 pence a shot.

Mapp in the UK is less than twice the price of propane, but we'll say twice, because I hear it's more expensive in the US.
No, I'll be generous. Three times. 2.4 pence a shot.

Cost of a potato: ~40 pence. I might get two shots from a potato if using a 1.5" barrel (which would make the chamber extreme overkill), so 20 pence of potato a shot.

20.8 pence for a Propane shot. 22.4 pence for a Mapp shot.
7.7% increase in cost. 10% increase in performance. Thus, a 2% increase in performance for each monetary unit spent. Most companies would kill for that.
It's a 3.8% increase in cost if MAPP is only twice as expensive, so a 6% increase in performance for each monetary unit spent.

I'm deliberately being generous on the cost of the gas, and I'm probably underestimating potato cost.
Given that gas is such a small fraction of money spent, then even a tripling of price there for a performance increase like 10% is worth it.

[jimmy101]

propylene = propene = C₃H₆ = CH₃-CH=CH₂

Which isn't on the SpudWiki Common Fuels page.
(Which I strongly recommend MrPed reads.)

Combustion formula:
2C₃H₆ + 9O₂ --> 6CO₂ + 6H₂O

Ignoring the 0.5% propane in the mix ...

So, for each propene you need 9/2 O₂'s. Air is ~21% O₂;
(2/9)(0.21)(100) = 4.67% by volume
if the propene displaces air from the chamber during fueling.

If the propane is injected into a sealed chamber then you need a bit more,
((0.0467)² + 0.0467)(100) = 4.9% by volume.

At least, that's the numbers I get.

[spudtyrrant]

propylene = propene = C₃H₆ = CH₃-CH=CH₂

Which isn't on the SpudWiki Common Fuels page.
(Which I strongly recommend MrPed reads.)

Combustion formula:
2C₃H₆ + 9O₂ --> 6CO₂ + 6H₂O

Ignoring the 0.5% propane in the mix ...

So, for each propene you need 9/2 O₂'s. Air is ~21% O₂;
(2/9)(0.21)(100) = 4.67% by volume
if the propene displaces air from the chamber during fueling.

If the propane is injected into a sealed chamber then you need a bit more,
((0.0467)² + 0.0467)(100) = 4.9% by volume.

At least, that's the numbers I get.

oh woops i went and rechecked the page i got my info from, and i realized those are the percentages for propylene oxide my mistake.

[jimmy101]

Cost of a potato: ~40 pence. I might get two shots from a potato if using a 1.5" barrel (which would make the chamber extreme overkill), so 20 pence of potato a shot.

I always get two shots/spud in a 2" barrel. Just cut the spud in half.

Most companies would kill for that.

Yes they would if the system was already optimized. Since a combustion spudgun is hardly optimized then I doubt the increased cost is justifiable. For a fraction of a pence per shot you could just use a larger chamber and get the same performance boost.

Or, do the math a bit differently. My ammo is free, since we have several crab apple trees and apples work great in a 2" barrel. So expendable cost per shot is 100% due to the fuel cost. So 0.8 pence/shot to 2.4pence/shot is a 300% increase in cost per shot for a 10% increase in performance.