Review on Radio Frequency Based Monitoring of SCR and Three Way Catalysts
Knowledge of the actual catalyst state plays a key role in automotive exhaust gas aftertreatment. The oxygen loading degree of three-way catalysts (TWC), the amount of stored ammonia in selective reduction catalysts (SCR), or the NOx loading degree in NOx storage catalysts (NSC) are important parameters. Today, they are determined indirectly and/or model-based, applying models that are typically calibrated by gas sensors installed up- and/or downstream of the catalysts. A novel approach to determine directly the catalyst state by microwaves (radio frequencies, rf) emerged recently. For this method, the catalyst housing serves as an electrical cavity resonator. As “sensor”, one or two simple antennas are mounted in the canning. The electrical properties of the honeycomb incl. coating change with gas loading, affecting either the resonance frequencies or the power transmission. Such contactless-obtained information is strongly correlated with the catalyst state as will be discussed here for TWC and SCR systems. This contribution reviews the progress in the past 3 years that exceeds by far the status of initial studies.
KeywordsOn-board diagnostics (OBD) Exhaust gas aftertreatment Microwave cavity perturbation Radio frequency sensor Selective catalytic reduction (SCR) SCR ammonia storage Three-way catalyst (TWC) Oxygen storage (OSC) Lambda probe
R.M is indebted to the German Research Foundation (DFG) for financial support under Grant Numbers MO1060/13-1 and MO1060/19-1.
- 2.Sappok A, Bromberg L (2010) Loading and regeneration analysis of a diesel particulate filter with a radio frequency-based sensor. SAE paper 2010-01-2126. doi: 10.4271/2010-01-2126
- 5.Masoudi M, Sappok A (2014) Soot (PM) Sensors. DieselNet Technology Guide. http://www.dieselnet.com/tech/dpf_soot_sensors.php. Accessed 07 Aug 2014
- 6.Nanjundaswamy H, Nagaraju V, Wu Y, Koehler E, Sappok A, Ragaller P, Bromberg L (2015) Advanced rf particulate filter sensing and controls for efficient aftertreatment management and reduced fuel consumption. SAE Technical Paper 2015-01-0996, doi: 10.4271/2015-01-0996
- 12.Birkhofer T, Hofmann P, Knezevic A, Moos R, Plog C, Schneider R (2003) Verfahren zur Erkennung des Zustands eines Katalysators mittels Mikrowellen. German Patent Specification DE 10358495 B4Google Scholar
- 13.Moos R, Spörl M, Hagen G, Gollwitzer A, Wedemann M, Fischerauer G (2008) TWC: lambda control and OBD without lambda probe—an initial approach. SAE paper 2008-01-0916, doi: 10.4271/2008-01-0916
- 15.Reiß S (2012) Direkte Zustandssensorik von Automobilabgaskatalysatoren (Direct diagnosis of automotive exhaust gas catalysts), Doctoral thesis, Universität BayreuthGoogle Scholar
- 17.Beulertz G, Votsmeier M, Herbst F, Moos R (2012) Replacing the lambda probe by radio frequency-based in-operando three-way catalyst oxygen loading detection. The 14th International Meeting on Chemical Sensors, IMCS 14, Nuremberg, Germany, 20–23 May 2012, pp 1426–1428, doi: 10.5162/IMCS2012/P2.2.7
- 24.Pihl J, Daw S (2014) NH3 storage isotherms: a path toward better models of NH3 storage on zeolite SCR catalysts. Presentation at 2014 DOE Crosscut Workshop on Lean Emissions Reduction SimulationGoogle Scholar
- 30.Dietrich M, Rauch D, Porch A, Moos R (2014) A laboratory test setup for in situ measurements of the dielectric properties of catalyst powder samples under reaction conditions by microwave cavity perturbation: set up and initial tests. Sensors 14:16856–16868. doi: 10.3390/s140916856 CrossRefGoogle Scholar