Gregor Beulertz

Dual mode NOx sensor: measuring both the accumulated amount and instantaneous level at low concentrations.

The accumulating-type (or integrating-type) NOx sensor principle offers two operation modes to measure low levels of NOx: The direct signal gives the total amount dosed over a time interval and its derivative the instantaneous concentration. With a linear sensor response, no baseline drift, and both response times and recovery times in the range of the gas exchange time of the test bench (5 to 7 s), the integrating sensor is well suited to reliably detect low levels of NOx. Experimental results are presented demonstrating the sensor’s integrating properties for the total amount detection and its sensitivity to both NO and to NO2. We also show the correlation between the derivative of the sensor signal and the known gas concentration. The long-term detection of NOx in the sub-ppm range (e.g., for air quality measurements) is discussed. Additionally, a self-adaption of the measurement range taking advantage of the temperature dependency of the sensitivity is addressed.

Overview: Status of the Microwave-Based Automotive Catalyst State Diagnosis

The oxygen loading degree in TWCs, the amount of stored ammonia in SCR catalysts, the NOx loading degree in LNTs, or the soot loading of DPFs play a key role in automotive exhaust gas aftertreatment. Today’s methods determine the catalyst state indirectly. They utilize gas sensors installed up- or downstream of the catalysts and the catalyst state is inferred from the sensor signals. This overview reports on the status of an alternative approach based on the interaction of electromagnetic microwaves with the catalyst material. Since the catalyst state is strongly correlated with the electrical properties of the catalyst material itself, this concept shows a great potential.

Microwave Cavity Perturbation as a Tool for Laboratory In Situ Measurement of the Oxidation State of Three Way Catalysts

Three-way catalyst-based automotive exhaust gas aftertreatment is of high importance to meet today’s emission standards. To determine in situ the oxygen loading state of three-way catalysts, a microwave cavity perturbation method is used. In this study, it is investigated whether this measurement setup that had originally been described for full-sized catalysts can be transferred to a lab test bench using cores of 1″ diameter. The initial tests were successful and a high correlation between the oxygen loading degree dependent resonance frequency and the conversion was found. As an application example of the new in situ characterization technique, the steady state degree of oxidation of a three way catalyst was measured as a function of the exhaust stoichiometry. The experimental results are compared with the prediction of a recently published improved kinetic model that takes into account the oxidation of reduced ceria by H2O and CO2. It is shown that the experimental observations agree very well with this improved model. This result provides evidence that under typical operating conditions, the degree of oxidation of the three way catalyst is controlled by equilibrium effects.

Replacing the lambda probe by radio frequency-based in-operando three-way catalyst oxygen loading detection

A novel strategy for closed-loop controlling the stoichiometric combustion of gasoline engines is presented. In contrast to common strategies which use the signal two lambda probes up- and downstream of a three way catalyst to control the engine, here the oxygen loading degree of a threeway catalyst is directly and in-operando determined by a radio frequency-based method and used as the process variable. Initial tests at a high dynamic laboratory test bench show that such a controlling strategy may lead to much lower emissions. Hence, there is a chance to replace lambda probes.

Cumulative Measurement Principle For The Detection Of Small Amounts Of Gaseous Species

To control or monitor processes and the compliance with air quality regulation, highly selective and long‐term stable gas sensors with a high accuracy in the low ppm detection range are needed. Gas sensor techniques detecting the actual concentration of analyte species often suffer from inaccuracy at low concentrations and signal instability. In contrast, gas sensors detecting the cumulative analyte amount during the measurement period are beneficial for monitoring very small amounts. The idea of the cumulative detection principle is the accumulation of the gas molecules in the sensitive layer and therefore measuring the timely integrated concentration of the gas species (“the amount”). Hence, the sensitive layer of the cumulative sensor consists of a gas storage material, which is able to store selectively the analyte molecules via a chemical bonding and thereby changes its electrical properties. In this work, the principle and the benefits of the cumulative detection is described. As an example, measure...