Tire gas

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Instead of compressed air for filling car tires , nitrogen is promoted by tire dealers as tire gas or tire inflation gas under various trade names. Correspondingly filled tires are marked with colored valve caps .

Car tire filled with gas, marked with a green valve cap

Tire gas is in tires of passenger aircraft , racing wheels, dangerous - trucks , vehicles for use in tunnels and mines and 1-formula used -cars to z. B. to minimize the risk of fire development and promotion in the event of a bursting tire or to prevent self-ignition due to a defective tire or a tire operated with significantly too low air pressure or an overheated brake system. This advantage cannot be transferred to normal car tires. Commercial vehicle tires on trucks are exposed to significantly higher loads (for normal trucks up to 6000 kg permissible total weight per tire) and the friction is higher. A defective tire or a stuck brake on a single wheel (especially on a semitrailer or trailer) is less noticeable to the driver due to the larger number of axles and tires, even while driving. The internal tire pressure (usually between 7 and 10  bar ) and the amount of air inflated are significantly higher than that of car tires, there are large quantities of highly fire-prone materials on the truck (tarpaulin, loads, etc.), and particularly strict safety regulations apply to the transport of dangerous goods to be observed to minimize risk. In the case of commercial aircraft, the landing places very heavy loads on the aircraft tires , since they are accelerated very quickly when they touch down on the runway.

composition

"Tire gas" based on nitrogen has a content of 85 to 99.99% of this inert gas . For comparison: air (and therefore also compressed air) contains around 78% nitrogen.

Nitrogen is obtained on an industrial scale by liquefying air using the Linde process . A relatively inferior quality (low purity with residues of oxygen) is sufficient for tire gas, since car tires are usually not flushed with nitrogen and therefore always contain residual air and thus residual oxygen (see also below).

In the case of larger aircraft, filling with pure nitrogen (typically 10 bar) is prescribed by an airworthiness directive from the FAA . For special weight-critical applications in aerospace, helium is also used as a tire filling.

The disc brakes of a large aircraft can u. U. develop so much heat that they can reach up to 1000 ° C and heat up the rims. To ensure that no tire bursts from overheating in an emergency (due to an increase in internal pressure and a decrease in material strength), a safety fuse is built into each aluminum rim, which melts when a certain temperature is reached and thus deflates the tire, while the brake disc is also cooled with the escaping gas becomes.

Tires used in Formula 1 racing are also filled with nitrogen, which is also used to drive the "compressed air" screwdriver to change wheels for safety reasons .

The price of a 50 liter 200 or 300 bar bottle of nitrogen is only marginally higher than that for the same amount of compressed air. For reasons of corrosion protection, such gases are always thoroughly dried so that no condensation forms under the high pressure in the bottle, which could possibly cause corrosion on the bottle.

Up until around the year 2000, car tires could be filled with SF 6 ( sulfur hexafluoride ), which was comparatively expensive at around DM 100  ( 51 ) per set of tires . However, SF 6 is a greenhouse gas with high potential. Since July 4, 2007, SF 6 may no longer be used for filling vehicle tires in the European Union in accordance with “ Regulation (EC) No. 842/2006 of the European Parliament and of the Council of May 17, 2006 on certain fluorinated greenhouse gases ”. In several European countries this application was banned at an earlier point in time or a ban was planned, in particular:

  • Denmark: Danish EPA 2001
  • Austria: HFC-FKW-SF6-VO 2002
  • Switzerland: Substance Ordinance 2003 (StoV), effective from 2004

Promotional arguments for tire gas

Is advertised with, among other things

  • Reducing the diffusion of oxygen through the tire
  • Resistance of tire pressure at different temperatures
  • Improvement of driving comfort in terms of suspension and rolling noise
  • Reduced consumption due to the lower rolling resistance of the tire
  • no oil vapors in the tire gas, which improves the durability of the tire
  • no moisture in the tire gas, thus reducing rust on the rim and valve
  • Lower fire risk in the event of overheating, since no ignitable mixture can form inside the tire due to a lack of oxygen .
  • Dealers and petrol stations expect the product to increase their earnings in the tire trade and improve customer loyalty . Potential competitive advantages result indirectly from this .

This “special” filling motivates the customer to visit his specialist dealer to check the tire pressure and refill, as “tire gas” is only available at a few petrol stations . Tire gas is therefore not only an opportunity for specialist retailers to generate sales themselves by selling the gas , it is also an effective means of customer loyalty and sales promotion .

Arguments against tire gas

The technical argument "pro tire gas" is criticized with the following arguments:

The "tire gas effect" is also achieved without the expensive special filling.
The following argument assumes that the "tire gas effect" exists at all significantly : The "normal compressed air" consists of 78% nitrogen. If this air diffuses faster through the tire, then the volatile components are 21% oxygen molecules. This portion should then have diffused out after a short time, the nitrogen remains behind. The only slight refilling then means that the nitrogen content will increase sharply within a short time.
Tire pressure not more even at different temperatures.
Tire pressure as a function of temperature
At pressures in the range of a few bar (i.e. also at 10 bar in truck tires) and real temperatures (−50 ° C to +150 ° C), all gases behave as almost ideal gases , regardless of whether they are 100% Nitrogen or just 78 percent nitrogen (= air).
After filling with tire gas, the nitrogen content only increases from 78% to 93%.
A car tire is inflated with around 2 bar overpressure . The ambient pressure (before filling) is 1 bar, so the pressure is tripled. This means that twice the amount of gas is pumped into the tire that was already present in the depressurized tire after it was pulled onto the rim. Since the tire is neither evacuated nor flushed in a protective atmosphere when it is filled with tire gas , the tire contains 66% tire gas and 33% air after filling, so the nitrogen content only increases by around 15%.
There is no distinction between roll and spring properties.
At the comparatively low pressures in vehicle tires, both oxygen and nitrogen molecules behave as almost ideal gases and are therefore identical in the range of a few per thousand.
Relation to aviation and Formula 1 not relevant in practice.
The temperature loads on tires that occur in Formula 1 racing and when aircraft are landing are far from being reached in road traffic. In road traffic, there is a risk of fire for the tires due to tire overheating as a result of insufficient pressure and the resulting flexing work . However, inflating the tire cannot reduce these risks.
Oil and water have no place in normal compressed air either.
The argument of the specialist dealer " Tire gas is free of oil vapor and moisture " means in reverse conclusion " Our normal compressed air system (with water and oil separator ) is inadequate. "And explains why in discussion forums to the question" My tire dealer offers me tire gas, what should I do? "One of the standard answers is:" Go to another tire dealer ".
The pressure loss due to diffusion through the rubber has no practical relevance.
The vehicle inspection intervals are sufficient for pressure loss due to diffusion . In practice, the relevant pressure loss is caused by defective valves or defects in the rim flange. In addition, the tire gas does not protect against mechanical injury of the tires as cuts or retracted nails.
Tire gas does not release you from regular tire pressure checks.

In addition, no verifiable advantages are known to date that justify pure nitrogen compared to the usual filling with normal air in vehicle tires for road traffic .

swell

  1. AD 87-08-09 FAA
  2. http://www.wer-weiss-was.de/t/stickstoff-im-flugzeugreifen/3257687/2 - Link not relevant.
  3. volkswagen-umwelt.de  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. Volkswagen does not recommend the use of SF 6 .@1@ 2Template: Toter Link / www.volkswagen.de  
  4. Katja Becken et al .: Avoiding fluorinated greenhouse gases: Ways to get out , Climate Change 08/2010, Umweltbundesamt.de, p. 2.

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