Nitrogen Tire Inflation

[mvw2]

Oh, I'm all about the sarcasm, lol. It's one trait I picked up from my dad, lol.

In terms of benefit, I asked math and math said no. CapriRacer seems to confirm that.

It's simply that the properties of nearly pure Nitrogen and air is nearly the same in all meaningful properties. It just doesn't do anything different. All the properties between each is just so close that any minute difference just isn't meaningful. For multi-billion dollar racing where a tiny, tiny bit of advantage means winning, nitrogen has its place. However, I think they too are being fed a good amount of marketing b.s. Still, the differences on that level are "significant" enough to consider the use. For consumer use, a butterfly can flap its wings in Argentina and any benefit you had would be lost. It's really just a matter of scale.

 

[sprintman]

Nitrogen in all three vehicles. Checking tire pressures is my biggest hate bar none. Nitrogen fill fixes that.

 

[TwoLostMinds]

Originally Posted By: CapriRacer
We tire engineers have always thought that it did not matter what the gas was that was used for inflation purposes - the tire reacted to being inflated, not the inflation medium.

Here are 2 graphs presented by Walter Waddell of ExxonMobil to the California Air Resources Board on June 4, 2008.

http://www.geocities.com/barrystiretech/n2cavitytemp.jpg

http://www.geocities.com/barrystiretech/n2rr.jpg

Both of these show no difference between N2 and air for 2 very important tire properties - Rolling Resistance and Operating Temperature.

Tire Aging?

The Law of Gas Partial Pressure says that oxygen would leak into the air chamber, in spite of there being an overall higher pressure in the chamber. This has been demonstrated, but I can't put my hands on a copy of the presentation made at the Sept 2007 Tire Society paper that shows the supporting data. When I find it, I'll post it.

But in the meantime, it is expected that oxygen would migrate into the rubber of the tire - and while the overall degradation rate would be slower, it would still happen. The question then becomes how much longer would it take before the degradation would become critical. The fact that oxygen can be detected in the air chamber - and the O2 volume increases over time - and the important area is halfway into the tire (the edges of the belt) - well ..... it's questionable that this difference would be enough to warrant the expense of using N2 as an inflation medium.


Thank you Capri. Now, this is far more convincing of a reason not to use nitrogen than "I wouldn't waste my money on it" or "its a scam". We will still have our tires filled with nitrogen when we pick up our Escape at the dealership but only beacause they are throwing it in for free. After that it will be air all the way.

 

[George Bynum]

Originally Posted By: CapriRacer

http://www.geocities.com/barrystiretech/n2cavitytemp.jpg


Does that show lower pressures at higher temperatures? What is the "cavity" being discussed.

That graph doesn't seem to fit at all the P1*V1*T2=P2*V2*T1 I understand ... yes, I converted to absolute units, but _ASSUMED_ the volume to remain constant.

 

[Quattro Pete]

The way I understood it is that they measured the temps inside the tire (the space betw. rim and tire - the cavity) for various inflation pressures. For example, they first inflated the tires to 24 PSI, then drove on those tires and found out that the temp inside the cavity reached 105.5 degrees F. When they inflated the tires to 26 PSI, the temp reached 104.5 degrees F, and so on.

I'm not a tire engineer, but I believe the reason this happens is that an underinflated tire flexes more as in rolls, and that flex results in significant heat being generated.

 

[itchrelief]

Originally Posted By: George Bynum
Originally Posted By: CapriRacer

http://www.geocities.com/barrystiretech/n2cavitytemp.jpg


Does that show lower pressures at higher temperatures? What is the "cavity" being discussed.

That graph doesn't seem to fit at all the P1*V1*T2=P2*V2*T1 I understand ... yes, I converted to absolute units, but _ASSUMED_ the volume to remain constant.


I agree with Quattro Pete in that this is probably more of a simulation of a tire and not strictly an isolated gas situation where P1*V1/n1/T1 = P2*V2/n2/T2 would directly correlate any two points on the graph.

That equation assumes an isolated sample of gas with no heat exchange with its surroundings. A situation akin to if you had an air-filled thermos with a plunger in it, and you pushed on the plunger to compress the air.

A tire exchanges heat with its surroundings. In a tire, any one-time temperature change in the tire's air (ie from a P1*V1/n1/T1 = P2V2/n2/T2 incident) will, over time, go away, as heat is exchanged with the ambient air.

The only difference in temperatures would occur if you had a sustained source of heat input to the tire and tire air cavity (as Quattro Pete stated, from the flexing) that exceed the tire's ability to dissipate that heat.

The tire and air chamber temperature would then rise as energy accumulated until the tire's heat exchange with the ambient air increased enough (due to increased temperature difference with the air) to balance out this heat input.

I believe it is this situation that is being graphed, and shows that there is little difference between air and pure nitrogen fill.

 

[Volvohead]

Of course, there's that special 78% nitrogen formula too.

Otherwise, I guess helium could reduce unsprung weight and improve mileage . . .

Keeping pressures regularly checked is the right way. A leaking tire will leak whatever's in it. Seasonal variations aren't that big a deal.

 

[Samilcar]

I run 100% hydrogen.

Oh the humanity...

 

[Greggy_D]

Originally Posted By: Samilcar
I run 100% hydrogen.

Oh the humanity...


Remind me not to smoke a cigar around your car.

 

[Shannow]

the risks of hydrogen while real are over-rated.

Generators at work are hydrogen filled, at 60psi, with 40 tonnes of copper and steel spinning through it at 3,000RPM and 22,000 volts.

It's only when air gets near it that it's bad.

 

[George Bynum]

Originally Posted By: Shannow
the risks of hydrogen while real are over-rated.

Generators at work are hydrogen filled, at 60psi, with 40 tonnes of copper and steel spinning through it at 3,000RPM and 22,000 volts.

It's only when air gets near it that it's bad.


Here in the USA, that's 3,600RPM ... and yes, I suspect all large generators are hydrogen cooled; they were in the 1920's even, but the pressures have increased. As for the dangers ... the areas around are carefully monitored, especially when they degas the seal oil. I've forgotten my specifics, but I believe that hydrogen is only "dangerous" between 4% and 90% concentration. One source says REALLY dangerous from 18% to 59%.

 

[Shannow]

George, they are still making air cooled 500MW units, but hydrogen is far more common.

I loathe the seal oil systems (probably because I look after them. Two face type seals, and two radial types)...and yes, there are hydrogen detectors everywhere.

 

[harry j]

Originally Posted By: George Bynum
Originally Posted By: Shannow
the risks of hydrogen while real are over-rated.

Generators at work are hydrogen filled, at 60psi, with 40 tonnes of copper and steel spinning through it at 3,000RPM and 22,000 volts.

It's only when air gets near it that it's bad.


Here in the USA, that's 3,600RPM ... and yes, I suspect all large generators are hydrogen cooled; they were in the 1920's even, but the pressures have increased. As for the dangers ... the areas around are carefully monitored, especially when they degas the seal oil. I've forgotten my specifics, but I believe that hydrogen is only "dangerous" between 4% and 90% concentration. One source says REALLY dangerous from 18% to 59%.



We have a 24 MW steam unit that's Hydrogen cooled and a 10MW unit that is air cooled. The hydrogen purity is closely monitered at all times, the alarm is set at 90% purity.

 

[Steve S]

Explain the hydrogen cooling ,is it like a air conditioner using liquid hydrogen as a refrigerant? or is it a different system?

 

[Shannow]

Steve,
the generators are pressure sealed, and full of hydrogen rather than air. The hydrogen is lighter, so windage is reduced (the OEM has advised us not to run past just over half rated revs with air in the casing). Hydrogen transfers heat pretty well too.

The generator rotor is fitted with a fan that blows the hydrogen along cooling slots in the rotor. When it comes out, it passes over some water cooled tubes to drop its temperature back down to go again.