Why nitrogen for prop governor

[falconvalley]

I'm glad some of you brought up the fact that Nitrogen is actually affected by temperature changes. It's not a big amount, but it's there. When I was brand new to fixing airplanes, an instructor told me temperature had absolutely no effect on Nitrogen and I couldn't figure out for the life of me, why I was having to let pressure out of the tires when we went from Milwaukee in the winter environment to the desert (or why my trainer was telling me to wait for the tires to cool before doing a tire pressure check). I guess I have forgotten all that important science stuff.

 

[z987k]

drive one in Az & Nv where air temps exceed 115-120 during the summer and you'll soon learn the advantage of nitrogen which expands far less than compressed air when heated...

Charles and Boyle would love to hear about this.
I know air isn't an ideal gas, but in case studies on the topic, pure n2 vs air from a 150psi tank both filled at 70F to 40psi, the change in pressure from 70F to 150F was .04psi.

Of more interest is that when 66 micrograms of liquid water is introduced to the tire(say during installation) the pressure difference between 70 and 150 vs the dry nitrogen and air(they performed identical like I said above) was 2psi at 150F and 14.7 at 212(duh).
Regardless of what is put in the tires, lube is going to be applied during mounting in most cases. However even then, for non racing environments, where your tire doesn't reach 212, it's of no consequence.

 

[Ajax]

Just a correction to your thread title-there is no nitrogen in the prop governor. The nitrogen would be in the propeller hub.

I realized that after I typed it but just let it slide.

 

[Chief Captain]

Why Nitrogen? Quite simple actually.

Nitrogen is *just about* as unreactive as you can get without using one of the noble gasses (He, Ne, Ar etc.)

But most importantly, nitrogen is dirt cheap, since it's about 80% of the air we breathe. If all you need is a compressed gas, then air may well be the cheapest option. But if you need something that's pure and/or inert, N2 is usually the most bang for your buck.

A few clarifications:

1. Oxygen is diatomic, just like Nitrogen. You would NOT want oxygen radicals floating around in your engine.

2. O2 is smaller than N2 mostly because Oxygen is more reactive. *This isn't 100% accurate, but it's good enough if you're not a chemist.

3. Comparing a pure sample of N2 to "air" is apples to oranges. N2 is much closer to an ideal gas than air. Air is about as far from ideal as you can get.

4. N2 is very much so affected by changes in temperature and pressure. PV=nRT

 

[sparky]

N2 is very much so affected by changes in temperature and pressure. PV=nRT

Nitrogen gas simply does not participate in any reactions at room temperature (or even at the higher temperatures found in small fires), and is therefore described as inert. Only at extremely high temperatures (such as those found near a lightning bolt or in an automobile's engine), or through the magic of "nitrogen fixing" bacteria (who work their trick with a complex set of enzymes instead of heat), can this triple bond energy be overcome, making nitrogen gas momentarily reactive while in an excited state.

We use nitrogen in the race shop and would not be using it for our purposes if it was effected by anything other than extreme temperatures. Goodyear Racing, BFGoodrich Racing, Firestone and every race shock manufacturer all specify the use of nitrogen because you can better maintain the desired pressure during the heat cycles experienced in both your tires and shocks during a race.

 

[z987k]

Nitrogen gas simply does not participate in any reactions at room temperature (or even at the higher temperatures found in small fires), and is therefore described as inert. Only at extremely high temperatures (such as those found near a lightning bolt or in an automobile's engine), or through the magic of "nitrogen fixing" bacteria (who work their trick with a complex set of enzymes instead of heat), can this triple bond energy be overcome, making nitrogen gas momentarily reactive while in an excited state.

We use nitrogen in the race shop and would not be using it for our purposes if it was effected by anything other than extreme temperatures. Goodyear Racing, BFGoodrich Racing, Firestone and every race shock manufacturer all specify the use of nitrogen because you can better maintain the desired pressure during the heat cycles experienced in both your tires and shocks during a race.

The first part is a good reason to use N2. The latter has been proven false when compared to dry air. In a shock, N2 is used because it is inert. Dry air displays the same properties as dry N2 through temperatures you find in most conditions - at lest 212 and below. Otherwise is in the face of Boyle, Charles and I guess Van Der Waals, but for these purposes the dry air is close enough to ideal, the equation works. Bottom line is the N2 not increasing in pressure less than dry air. It is inert at these temps though.