I read some of the post. As for nitrogen not leaking out as fast as air; I do not buy it. The atomic weight of nitrogen is 14.0067; air, which is ~78% air, ~just under 20% oxygen and just under 1 percent argon is given a (calculation mass weight of 28.7); You get the gas conversion rate by taking the square root of the first gas divided by the second gas, for the gas conversion rate.
Because nitrogen has less atomic mass than air, it will leak out faster than air. Air will actually leak out it’s constituents in their own respective leak rates, but, the matter is that nitrogen will leak out at the rate of air, multiplied by ~.7 rounded up. As for nitrogen preventing moisture, this will not happen either, as tire materials are organic polymers and never hermetic. Moisture will ingress through them. Only glass, metal and ceramics can be utilized to meet hermeticity requirements of MIL-STD-883, Method 1014, which defines leak testing. As for better mileage, I don’t buy it. A vessel filled with any gas will have one cummulative atmosphere; doesn’t matter what gas it is; the atmospheric pressure will be the vessel volume multipled by atmospheres of gas times volume resulting in units of ATM CC; That is to say that a tire inflated to 32 lbs with nitrogen, or 32 lbs of air, is still 32 lbs.
exellent
No. Permeation is something of a function of molecular size, which doesn’t necessarily scale with mass. Nitrogen will permeate rubber at a rate roughly one-fourth that of oxygen (for example, 25 v. 98 ccs per atm. per day per square meter for a 1mm thich sample of butyl rubber at 0C).
The argument isn’t that using nitrogen completely seals the tire from moisture, it’s that moisture isn’t introdced into the tire during filling by using non-dry air. As was pointed out, simply using dry air gives the same benefit.
The argument is that nitrogen-filled tires lose pressure more slowly than air-filled tires. Since lowering the pressure in tires reduces fuel economy, and nitrogen-filled tires will on average have a higher pressure (because they lose the pressure more slowly), nitrogen filling increases fuel economy. Only, with reasonably regular pressure checks, the difference for a passenger vehicle is small.
You obviously did not read the link that was previously supplied with respect to this topic. It explicitly explains that permeation is a function of molecular geometry and size, not atomic weight. Nitrogen gas is diatomic N[sub]2[/sub], oxygen gas is diatomic oxygen O[sub]2[/sub]. Air is, as you say, a mix of gases and each component of air will behave independently. Also, because oxygen has one more proton that nitrogen, it forms a stronger bond and pulls the electron shells in tighter. Plus the bond geometries between the molecules are at different angles. For these reasons, the nitrogen molecules are actually larger than oxygen molecules.
Do you agree a larger molecule will have a harder time fitting through a tiny hole?
It’s not about preventing all moisture, it is about relative quantities of moisture. Using nitrogen or dry air will prevent a large amount of the water from being included.
Think of it this way. Take two identical buckets, fill one halfway with water. Then set them outside in the rain. Assuming identical conditions, which one has more water in it at the end of the day?
Also consider if one of the gases is water vapor, atmospheric temperature changes can make some of that water condense. If the water condenses inside the tire, it gives less contribution to the total tire internal pressure.
At least I think we can all agree that inflating your tires with hydrogen would be a bad idea.
While road debris can sometimes cut or damage the rubber reinforcing material causing a blowout or permitting the pressure peak of a severe bump to rupture the tire, “Most blowouts are caused by too little air pressure allowing the tire to flex beyond its elastic limits until it overheats to the point where the rubber loses its bond to the internal fabric and steel cord reinforcement.” (http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=13) so I don’t think I’m out of line assuming a reduction of rubber degradation in that area will decrease your chances of a blowout. The Drexan study agrees, citing fewer road failures as one of the many N2 benefits.
As I have found no data indicating what percentage of blowouts are due to deteriorated sidewalls separating from the internal reinforcement as opposed to recently picking up a nail (with the resulting loss of pressure) – let alone how much they overlap to contribute to the failure - I can’t give you a hard number for blowout reductions due to nitrogen. The best I can do is present studies that show N2 inflation doubles the tire body strength over the life of the tire compared to air.
I found a more comprehensive summary of the Drexan study (http://www.nitroplus.com.au/assets/Results_of_a_Trial_of_Nitrogen_Tire_Inflation_in_a_Long_Haul_Trucking_2007_metric.pdf) but not the full 36 page report (perhaps one of our academics with archive access can help).
In addition to better pressure retention, the chemical reaction of oxygen breaks down the unsaturated bonds in rubber, converting long chain polymers into shorter, weaker chains with a similar result to the way soft, gummy racing tires reduce MPGs.
I would think the thinner, weaker rubber in automotive tires would benefit even more from slower aging than truck tires, I guess we’ll have to wait for a double blind 110 million tire mile study on car tires to settle this one.
As they were determining suitability for fleet conversions they used regular maintenance intervals rather than a daily check as a purely scientific study might have done.
Even if a different mechanism accounts for the 3.3% increase in mileage on their regularly maintained tires, it’s still a 3.3% increase.
I pay for my own tires, fuel and maintenance and I think they are high enough to spend a couple of bucks (even if I couldn’t get it for free) to get all the other slight to moderate advantages, including a substantial (IMHO) 26% increase in tire tread life and 50% stronger tire by the time they do eventually wear out the tread.
Since there are nearly 100 times more cars than semi’s in the US, think of all the lives, oil, pollution and money we’d save if we weighed N2 inflation on it’s own merits instead of assuming there was only a ‘very small benefit’ to using it.
We were in the nitrogen business (industrial gases, in general), and it was easy for us to use nitrogen. To my knowledge, testing was done in a qualified facility to see the difference in burning characteristics, ignition, rate of burn, etc. between normall aspirated tires and nitrogen ones…I think I recall seeing film. I don’t think the frequency of these fires could be gauged and controlled for tire manufacturer, ambient temperature, OTR vs. local, etc. What I’m saying is that in my fleet of 30 vehicles, using mostly 11/22.5 radials, we didn’t have any tire fires either before or after the change to nitrogen. Comparing results for miles of use per tire was a very long process and we had little data to compare to at our local location.
In other words, no startling results, only theoretically positive ones.
Why would a dipole molecule like oxygen leak more easily than a monopole like nitrogen? I suspect the oxygen reacting with the gummy stuff in the bead where the tire meets the rim, or, even, the seals in the valve stems.
to me, the technology that lets you keep an eye on tire pressure on all 18 tires on a rig is rather wonderful. I’m sure it pays for itself, sooner or later, independent of the gas used.
An aside. When inflating balloons, our old expert used to make a mixture of helium and carbon dioxide (99/1) claiming the carbon dioxide molecules would plug the interstices in the balloon, sealing it better. Our easy tests of his method revealed that he was right, inflation lasting twice as long with his mix.
Today, they use mylar to produce the same effect. I think a balloon mix helium would be worth considering if you owned a balloon inflating franchise…
O[sub]2[/sub] molecules are smaller than N[sub]2[/sub] molecules. (Because oxygen atoms are smaller than nitrogen atoms. In general, atoms get smaller going left to right on the periodic table, and then take a big jump up at every “carriage return”.)
I fill my tires with Radon. No interaction with the rubber. Large enough to not leak. Not flammable.
Yeah, but you have to re-do them twice a week, and they get coated with lead over time.