Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 01 Dec 2007

Numerical Model for Nitrogen Tire Inflation5

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Page Range: 300 – 316
DOI: 10.2346/1.2802612
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Abstract

The scope of this study was twofold: (1) to quantify the contribution nitrogen inflation would have on oxidative aging of tires and (2) measure the improvement nitrogen tire inflation may have on inflation pressure retention. A previously developed tool for diffusion-limited oxidation was used to simulate aging behavior at 25 and 60 °C. Oven-accelerated tire aging (60 °C) data for different inflation media was used for successful validation of the model, and it was shown that aging rates for higher oxygen concentrations tend toward a constant value. For lower temperatures, the use of nitrogen was shown to produce lower oxygen concentration in the wedge and bead regions of the tire geometry considered when compared to air inflation. By using 95% pure nitrogen (that is, the actual nitrogen concentration in the tire cavity), a 25% reduction in aging rate (for the tire wedge) and a 35% reduction in the initial flux of mass out of the tire (a measure of inflation pressure retention) were calculated.

Keywords: aging; oxidation; diffusion-limited oxidation; nitrogen inflation
Copyright: The Tire Society
FIG. 1.
FIG. 1.

Typical tire construction with key components labeled.

FIG. 2.
FIG. 2.

Oxygen uptake for low temperature from Terrill et al. [20] with curve double-exponential curve fit.

FIG. 3.
FIG. 3.

Typical mesh density used during a simulation as well as important tire features for tire A.

FIG. 4.
FIG. 4.

Comparison of oxygen concentrations at 25 °C for the cases of air (left) and nitrogen (right) inflation media.

FIG. 5.
FIG. 5.

Comparison of local oxygen consumption (−d[O2]∕dt) at 25 °C for the cases of air (left) and nitrogen (right) inflation media. Note that the butyl inner liner is not shown.

FIG. 6.
FIG. 6.

Model prediction with experimental results for the shift factor, SAir, for the wedge versus oxygen partial pressure in the tire.

FIG. 7.
FIG. 7.

Model prediction with experimental results for the shift factor, SAir, for the skim versus oxygen partial pressure in the tire.

FIG. 8.
FIG. 8.

Comparison of the form for the oxidation kinetics.

FIG. 9.
FIG. 9.

Comparison of rate of change for cross-link density in the wedge and skim regions of the tire as functions of mole fraction of oxygen for a 450 kPa tire. The wedge is shown to move toward being starved of oxygen as XO2 moves toward zero.

FIG. 10.
FIG. 10.

Total molar flow rate of fill gas versus nitrogen content for 450 kPa tire with improvement over the use of air.

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