Exhaust equilibrium oxygen partial

Figure 3. Exhaust gas equilibrium oxygen partial pressure as a function of the...

Zirconia sensors have been used primarily in the exhaust system of automobiles to control the air-to-fuel ratio for meeting the federal requirements on such noxious gases as carbon monoxide, methane and nitrogen oxides. The applicability of zirconia sensors for this particular application is based on the assumption that, under thermodynamic equilibrium, the partial pressure of oxygen in the exhaust gas depends primarily on the air-to-fuel ratio. To compensate for the fact that in reality equilibrium is not reached, catalytic platinum electrics are incorporated in the zirconia sensor design [Stevens, 1986]. In the zirconia sensor, the outside of the zirconia tube is exposed to the exhaust gas while the inside is exposed to the ambient air as a reference atmosphere. 

At high ceramic temperatures the oxygen vacancy equilibrium (V0) of the Ti02 lattice responds quickly to the change of the partial pressure of oxygen p02 in the exhaust gas (Fig. 5.6.4). 

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