Nitrogen--my experience

[smgutsch]

I came across this thread and found it interesting. But, I disagree with some of the comments.
1. Air is about 78% Nitrogen 21.3% oxygen.
Oxygen is a larger molecule than nitrogen (molecular weight of 32 vs 28).
The density of oxygen is a little higher than nitrogen. (1.33 vs 1.17 g/L)
2. The guys that died in the storage tank died from lack of oxygen. This type of accident has happened way too often. Thus the OSHA rules for oxygen monitoring during confined space entry.
If you empty your nitrogen filled tires in your closed garage you will be fine. It will take more than 4 tires to drop the oxygen content of the air to below 21%
3. Nitrogen narcosis and the "bends" happen because some gases will dissolve in the blood more rapidly than others at high pressures. (180 ft water pressure)
4. Aircraft manufactures are concerned because tires that get hot enough to auto ignite would also be filled with really hot oxygen that would support a runaway reaction (fire).
5. The reason nitrogen is used in racecars is because it is dry - no water. You could just as easily use really dry air, but because of the marketplace nitrogen is cheaper. Water vapor expands differently than air as the temperature changes. When it changes from liquid to vapor the volume really increases. If someone is constantly putting wet air in their tires there might be some concerns with pressure fluctuation.
6. Oxygen and ozone in the air might degrade the rubber faster but I agree that is would probably take a longer than what tires typically last.
7. A properly inflated tire is the best thing you can do. Higher tire pressure means lower rolling resistance and less heat build up. Over inflated tires lose traction and will skid in a cornering situation. And then there is tread wear.
8. Winter air is much better because it is drier, especially if it is obtained in the mountains where it is thinner.(insert smiley face icon)

I have been skeptical of all the claims. But, I was happy to read your research results.
Thank you for the excellent discussion.

 

[orezok]

The great thing about the internet is that if it's "published" it must be true! Yes, nitrogen molecules are smaller than oxygen, but not enough to ever make a difference.

Molecular size a bit tricky. As a quick comparison, if you use the covalent radius defined as 1/2 the distance between to identical covalently bonding nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's covalent radius is 75pm so the length of a nitrogen (N2) molecule ought to be 4 X 75pm or 300 pm. A molecule of oxygen (O2) ought to be just a shade smaller 4 X 73pm or 292pm. So an oxygen molecule is a little less than 3% smaller than a nitrogen molecule.

The real difference between plain old air and nitrogen is the water vapor difference. Water vapor expands at many times the rate of either dry air or dry nitrogen.

Many of your "budget challenged" racing teams use dry air instead of nitrogen due to cost. Most claim no difference, but that is subjective.

Longacre Racing Online -- Instructions "Air Dryer Instructions - P/N 50570"

 

[TheGoose]

I may be wrong here (long time since chemistry). O atomic #=16, N atomic #=14. O2=32 g/mol; N2=28 g/mol. Oxygen has the bigger molecule.

I sat in a meeting a while back with some tire experts and this subject came up. The consensus was it's a hoax. There is some agreement that pure nitrogen will leak down slower as the molecules are larger than oxygen and other constituents, but as Baucom already pointed out, regular air is 78% nitrogen anyway.

The other flaw is that in a normal tire shop there is no way to fully remove the normal air before the nitrogen fill so you will always have a mixture in the tire.

Best advice, spend $2 on green valve caps and save $38 in nitrogen.

 

[Youare]

I came across this thread and found it interesting. But, I disagree with some of the comments.
1. Air is about 78% Nitrogen 21.3% oxygen.
Oxygen is a larger molecule than nitrogen (molecular weight of 32 vs 28).
The density of oxygen is a little higher than nitrogen. (1.33 vs 1.17 g/L)
2. The guys that died in the storage tank died from lack of oxygen. This type of accident has happened way too often. Thus the OSHA rules for oxygen monitoring during confined space entry.
If you empty your nitrogen filled tires in your closed garage you will be fine. It will take more than 4 tires to drop the oxygen content of the air to below 21%
3. Nitrogen narcosis and the "bends" happen because some gases will dissolve in the blood more rapidly than others at high pressures. (180 ft water pressure)
4. Aircraft manufactures are concerned because tires that get hot enough to auto ignite would also be filled with really hot oxygen that would support a runaway reaction (fire).
5. The reason nitrogen is used in racecars is because it is dry - no water. You could just as easily use really dry air, but because of the marketplace nitrogen is cheaper. Water vapor expands differently than air as the temperature changes. When it changes from liquid to vapor the volume really increases. If someone is constantly putting wet air in their tires there might be some concerns with pressure fluctuation.
6. Oxygen and ozone in the air might degrade the rubber faster but I agree that is would probably take a longer than what tires typically last.
7. A properly inflated tire is the best thing you can do. Higher tire pressure means lower rolling resistance and less heat build up. Over inflated tires lose traction and will skid in a cornering situation. And then there is tread wear.
8. Winter air is much better because it is drier, especially if it is obtained in the mountains where it is thinner.(insert smiley face icon)

I have been skeptical of all the claims. But, I was happy to read your research results.
Thank you for the excellent discussion.

I have asked the question "why is nitrogen better to inflate a tire than plain air" many times of people in the tire business and got all different the different responces mentioned in this thread. The tire dealers are making a lot of easy money telling people things that were not valid.

The only reason nitrogen might have an advantage over plain air is that in the process of extracting it from the atmosphere it becomes a very dry gas. The water levels in compressed air could be lowered by the use of filters or refridgerated drying units an added expense that tire dealers can not charge extra for like they can for nitrogen.

The government has passed a law requiring all new cars and light trucks to have a tire pressure management system to alert the driver of a loss in tire pressure in an effort to prevent rollover accidents. The electronic pressure sensor now mounted insdie of all new tires might last longer if they were not exposed to damp air. These sensors can cost up to $200.00 each so repalacement costs can be significant over time.

I really think tire dealers are taking advantage of customers by selling them green valve stems and "air that has a llitte more nitrogen in it.

The place where I work uses nitrogen both in liquid and gas form, I do have a little experience working with both.

Randy

Randy

 

[Bedlam]

Just curious are there any special precautions when dismounting tires with these valve sensors? Just have to be sure to not hit them with the bead?

 

[Wis Bang]

I used to have to N2 purge chem trailers loading transformer oil [very hydroscopic] until we replaced the site air compressor w/ a Sulaire screw compressor w/ a twin dessicant tank dryer. Then we purchased a simple electronic hydrometer to measure the dew point of the air as we purged the freshly cleaned tankers. We would get it down to -40 or so and seal them up.

No more need to have a supply of N2 from ourr welding gas supplier and no more need to affix warning signs over the oxygen deficient atmosphere.

The mechanics liked not haveing to drain the water traps several times a day and said their air operated tools lasted much longer w/ less oil added then w/ the old compressor.

 

[2rex2]

I buy and use nitrogen to inflate aircraft tires that will reduce the explosive risk of fire. It is available at the local welding supply source for about $28. same bottle could inflate about 500 auto tires. when the ground moles become a problem i pump it in to the "runs" and they drown because of the lack of oxgen.would i use it in a car?..no