Abstract
The universal exhaust gas oxygen sensor (UEGO) is a device used to infer the combustion air-to-fuel ratio of an internal combustion engine by sampling the exhaust gas. The sensor operates using a feedback system to maintain a specified internal condition, and measures the oxygen current required for this. While the steady state operation of the sensor is reasonably well-understood – dominated as it is by the diffusion of gas species – the factors influencing the transient response are not so clear.In this paper a numerical model of a sensor is compared to experimental data. By examining the effect of the inclusion of different aspects into the model, it becomes clear that it is necessary to account for the influence of gaseous species adsorbing onto surfaces, as well as the more traditional approach based on oxygen partial pressure, to correctly capture the transient response of a sensor containing a Pt|YSZ|Pt cell.
Highlights
The universal exhaust gas oxygen (UEGO) sensor has become a commonplace as a method to determine the non-dimensional air-fuel ratio (λ) of ICPreprint submitted to Sensors and Actuators B: Chemical engines, and may form a part of a feedback control system of the engine
During experiments the UEGO is held at a temperature of 750◦C, a temperature where the YSZ will freely conduct oxygen ions
The resistance of the YSZ is interpreted via Ohm’s Law, and is a known function of temperature. This means the sensor heating circuit can be controlled via a feedback circuit to ensure the reference cell is maintained at an electrical resistance corresponding to the desired operating temperature
Summary
The universal exhaust gas oxygen (UEGO) sensor has become a commonplace as a method to determine the non-dimensional air-fuel ratio (λ) of IC. This is clearly seen in the sensor response to a sample gas crossing stoichiomtery [2] In this case the Nernstian potential of the pump cell changes very rapidly, and the sensor output departs from the value predicted by gas diffusion through the barrier. To explore this further, this paper will focus on the transient response of the UEGO in ambient air, and examine the mechanism by which the voltage across the reference cell is generated
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