Motor Vehicle Maintenance & Repair Asked on March 12, 2021
In critical applications tires are inflated using pure nitrogen (link).
But carbon dioxide (CO2) is a larger molecule (will leak slower from the tire), as well as inert (will not oxidize rim and will not combust in case of an accident). (link)
Also, from the ideal gas law, pressure is proportional to the density, individual gas constant and temperature. Assuming constant volume (i.e. P ∝ R*T), any change in temperature is “amplified” by the individual gas constant. And the gas constant is in favor of CO2: R(CO2) < R(O2) < R(N2). (ref) So CO2 seems to give better pressure stability over temperature fluctuations.
Also, CO2 storage is cheaper than nitrogen storage.
So why tires are inflated with nitrogen and not CO2?
Nitrogen is inert and doesn't affect rubber or the steel rim. Carbon dioxide is highly reactive and affects both the rubber by causing swelling in the rubber. It also would cause corrosion in iron based rims (particularly Carbon- Steel).
Edit: When CO2 is mixed with moisture becomes Carbolic acid which is corrosive. It all depends on concentration. It is like comparing Acetic Acid commonly referred to as Vinegar. At 3% you can put on french fries. At industrial strength 97% not only will it dissolve the french fry but also human flesh right down to the bone very fast. As for CO2 affect on rubber I cited a industry source-(Air Liquide) a company that specialized in compressed gases.
In the case of automotive tires using CO2 would probably cause catastrophic failure. My experience with Nitrogen is that I have noticed it to be much more quieter while driving and less pressure variations when the temperature varies from season to season.
http://encyclopedia.airliquide.com/encyclopedia.asp?LanguageID=11&GasID=26
Check under Material Compatibility under the heading of Elastomers- Quite illuminating.....
Correct answer by Old_Fossil on March 12, 2021
Nitrogen makes up around 80% of Air - therefore its more readily reclaimed and separated than the smaller amounts of other gases in air. I.e. the process for reclaiming nitrogen from air could be less efficient than that of reclaiming CO2 from air and still be cost effective. Additionally its stability at higher temperatures means its behaves more predictably and means the tyres handling characteristics are consistent.
Answered by Mauro on March 12, 2021
Nitrogen is a very predictable gas. All of its behaviors have been tested rigorously over many many years. As such they can predict the behavior much more easily than a mixed gas. Also, its performance is very similar to air. If you were unable to have access to a bottle of nitrogen, you could still use normal air and still be close to the original performance.
From a safety perspective, nitrogen contains no oxygen. If there were an accident there is no oxygen to propagate a fire (air contains ~21% oxygen).
Answered by Kris on March 12, 2021
Nitrogen is cheaper because it's readily available in the air, and can be extracted with a rather compact nitrogen generator. Extraction of carbon dioxide from the air is inefficient, so it has to be produced by burning fuels (such as methane) or via thermal decomposition of limestone.
Answered by Dmitry Grigoryev on March 12, 2021
Primarily two reasons:
Of course, you can argue that since CO2 is a bigger and heavier molecule then it will leak more slowly from your tires (about 20% more slowly per Graham's Law!), but I believe that to be largely overshadowed by the two points mentioned above.
Answered by ManRow on March 12, 2021
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