TY - JOUR A1 - Walter, Stefanie A1 - Schwanzer, Peter A1 - Steiner, Carsten A1 - Hagen, Gunter A1 - Rabl, Hans-Peter A1 - Dietrich, Markus A1 - Moos, Ralf T1 - Mixing Rules for an Exact Determination of the Dielectric Properties of Engine Soot Using the Microwave Cavity Perturbation Method and Its Application in Gasoline Particulate Filters JF - Sensors N2 - In recent years, particulate filters have become mandatory in almost all gasoline-powered vehicles to comply with emission standards regarding particulate number. In contrast to diesel applications, monitoring gasoline particulate filters (GPFs) by differential pressure sensors is challenging due to lower soot masses to be deposited in the GPFs. A different approach to determine the soot loading of GPFs is a radio frequency-based sensor (RF sensor). To facilitate sensor development, in previous work, a simulation model was created to determine the RF signal at arbitrary engine operating points. To ensure accuracy, the exact dielectric properties of the soot need to be known. This work has shown how small samples of soot-loaded filter are sufficient to determine the dielectric properties of soot itself using the microwave cavity perturbation method. For this purpose, mixing rules were determined through simulation and measurement, allowing the air and substrate fraction of the sample to be considered. Due to the different geometry of filter substrates compared to crushed soot samples, a different mixing rule had to be derived to calculate the effective filter properties required for the simulation model. The accuracy of the determined mixing rules and the underlying simulation model could be verified by comparative measurements on an engine test bench. KW - mixing rule KW - dielectric properties KW - microwave cavity perturbation KW - finite element method (FEM) KW - soot mass determination KW - radio-frequency (RF) KW - gasoline particulate filter (GPF) Y1 - 2022 U6 - https://doi.org/10.3390/s22093311 VL - 22 IS - 9 SP - 1 EP - 17 PB - MDPI CY - Basel ER - TY - GEN A1 - Walter, Stefanie A1 - Schwanzer, Peter A1 - Hagen, Gunter A1 - Rabl, Hans-Peter A1 - Dietrich, Markus A1 - Moos, Ralf T1 - Combined Ash and Soot Monitoring in Gasoline Particulate Filters with a Radio-Frequency-Based Sensor T2 - SAE World Congress Experience, April 5-7, 2022, Detroit, Michigan, USA N2 - In recent years, it turned out that primarily the number of ultrafine particles and not their mass is relevant in terms of harmful health effects. Therefore, exhaust emission standards are constantly being tightened with regard to the particulate number. To meet the emission limits, particulate filters have become necessary for gasoline engines. Similar to diesel applications, gasoline particulate filters (GPFs) can be monitored via differential pressure measurement or via a radio-frequency approach (RF-sensor). The latter is based on the influence of the soot conductivity on the electromagnetic field. To control the GPF, ash detection is of crucial importance besides the soot load monitoring. With the differential pressure system, this is only possible with high uncertainties due to the low pressure increase caused by ash. The RF-sensor, however, has already demonstrated its potential for ash detection in diesel applications. In order to verify the applicability of the system for GPFs, filters were loaded via a method for fast ash loading. Thereby, it was shown that by evaluating resonant modes – especially the resonant frequency – the ash loading can easily be measured as long as the filter is soot-unloaded. In contrast, soot loading can be determined independently from this by considering a frequency-averaged transmission signal between the antennas of the RF-sensor. Using a setup for radio-frequency material characterization, the dielectric parameters of the generated ash were also measured. In comparison with the properties of the synthetic soot PrintexU, ash showed significantly lower dielectric losses. Thus, the evaluation of the loss-dependent quality factor, which is only possible at low soot loadings, allows a precise conclusion whether the filter is completely soot-free. Furthermore, using synthetic soot loading, it could be shown that soot detection via the averaged transmission signal is not affected by ash. In summary, it could be shown that with the RF-sensor, ash and soot can be simultaneously detected. Y1 - 2022 UR - https://eref.uni-bayreuth.de/id/eprint/69506 ER -