Abstract
Abstract. By applying the pulsed polarization technique, a thimble-type lambda probe can be used as a NOx sensor in the low ppm range. Due to the robustness of the sensor in harsh exhaust gas environments, this approach has many opportunities for application. The temperature operating range for best NO sensing properties is a crucial parameter. The sensor temperature changes with the ambient gas temperature, but can be stabilized actively by internal heating in a certain temperature range. This study evaluates in detail the temperature influence on NO sensitivity, so that an optimum operating point can be derived from these results using a dynamic measurement technique. Stepwise NO concentration changes between 0 and 12.5 ppm in synthetic exhausts demonstrate the potential of the concept.
Highlights
Environmental issues like acid rain and smog are caused by oxides of nitrogen (NOx), so that strong emission regulations have been introduced for automotive emissions
The sensor operation temperature of a thimble-type lambda probe was varied by different gas temperatures as well as by different heater voltages
The sensors were operated in the pulsed polarization technique, and the discharge curves after both polarization signs as well as the sensor responses regarding low NO concentrations (10 ppm range) were evaluated in detail
Summary
Environmental issues like acid rain and smog are caused by oxides of nitrogen (NOx), so that strong emission regulations have been introduced for automotive emissions. It is possible to operate a commercial thimble-type lambda probe as a promising NO sensor just by applying a so-called pulsed polarization technique (Fischer et al, 2010). This study raises and answers the question of whether the lambda probe can be applied as a NO sensor in a large temperature range only by controlling the heater voltage depending on ambient temperature. This information is essential for the development of an operating strategy and a possible sensor application. The discharge curves of the sensor after polarization pulses as well as polarization currents during voltage pulses are recorded at different external gas temperatures and internal heater voltages
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