Multi-gas sensor to detect simultaneously nitrogen oxides and oxygen

Abstract

Abstract. Due to tightened emission limits, the efficiency of exhaust gas aftertreatment systems has to be further enhanced. Therefore, inexpensive and robust NOx sensors are required to be installed not only in automotive exhausts, but also in any other kind of combustion-based application. In this contribution, an impedimetric NOx sensor is presented. The impedance of a functional thick film (KMnO4, manufactured in a screen-printing technique on planar alumina substrates) depends selectively on the NOx concentration in the exhaust but shows a dependency on the oxygen concentration. Therefore, an additional temperature-independent resistive oxygen sensor structure was integrated on the same sensor platform. BFAT (BaFe0.74Al0.01Ta0.25O3−δ (BaFe0.74Al0.01Ta0.25O3−δ) was used for this purpose, and the measurement was conducted in the dc resistance mode. It serves not only to determine the oxygen concentration in the exhaust, but also to correct the oxygen dependency of the NOx sensor.

Application of a Robust Thermoelectric Gas Sensor in Firewood Combustion Exhausts

“…Further developments regarding the sensing element might also address the integration of an oxygen sensor that is similar to the one as described in [ 25 ].…”

Methods to investigate the temperature distribution of heated ceramic gas sensors for high-temperature applications

“…Here, the resistance of the heater structure behaves similarly to a platinum resistance thermometer. Thus, the measured heater resistance can be used to calculate the temperature of the heater structure (T H ) and to control it with appropriate electronics (Herrmann et al, 2020). This calculation represents an average value of the resistance over the area considered by the four-wire measurement, which cannot detect temperature inhomogeneities within the structure.…”

“…Depending on the application of the sensor, the error tolerance should be in a range around 10 % of the exact value (United Nations Economic Commission for Europe, 2013). This effect may be corrected with extensive efforts by the use of secondary signals, such as the heating power or load state of the plant (Ritter et al, 2017;Hagen et al, 2023).…”

Resistive Multi-Gas Sensor for Simultaneously Measuring the Oxygen Stoichiometry (λ) and the NOx Concentration in Exhausts: Engine Tests under Dynamic Conditions

“…At high temperatures, the electrical resistivity of the material was determined by the balance of sorption and desorption, which was also affected by the p O2 in the environment [ 9 , 10 , 12 , 13 ]. A higher p O2 favored nitrate formation and simultaneously affected both the base resistance and the NO x sensitivity of the sensor film [ 9 , 14 ]. Under real exhaust gas conditions, knowledge of the exact oxygen concentration, or oxygen stoichiometry λ , in the exhaust gas is therefore essential for evaluating the NO x concentration c NO x .…”

“…Initial investigations were also performed on the combined sensor setup (multi-gas sensor), but were limited to measurements in synthetic gas mixtures that simulate real exhausts [ 14 , 15 ]. Therefore, the aim of this study was to analyze the sensor concept under dynamic conditions in the exhaust gas of a diesel engine.…”