On-Board Measurements of Ammonia Storage on SCR and Combined SCR Filter Systems using Radio Frequency Sensors

Paul  Ragaller, CTS Corporation, Boston Innovation Office

Achieving ultra-low NOx emissions levels requires precise information of the operation state of the SCR system.  Such information enables maximum NOx conversion over all operating conditions via direct feedback control.  Currently these systems rely on a variety of gas sensors, mounted upstream or downstream of the catalyst, which only provide an indirect inference of the operation state.  In this study, a radio frequency (RF) sensor was used to measure the ammonia loading state of catalyst systems.  The technology was applied to core samples on bench reactors and full-scale system evaluations on a light-duty and heavy-duty engine applications.

The evaluations utilized radio frequencies to monitor ammonia adsorption levels on the catalyst via changes in the bulk dielectric properties of the cavity within selected regions of the RF spectrum.  Sensor output was provided as feedback in the implementation of a closed loop SCR control strategy through the engine evaluations.  Additional work extended the application of RF sensing to monitor stored ammonia in the presence of soot and ash on combined SCR + Filter (SCRF) systems which allow for the simultaneous reduction of both particulate matter and NOx emissions.  The approach utilized the RF sensor to directly measure soot in the filter, which exhibits a large dielectric loss.  Stored ammonia levels were determined by feeding selected RF spectral features into a pretrained Generalized Regression Neural Network (GRNN) model.  The results indicate significant potential towards removing the control barriers typically associated with the implementation of advanced SCRF systems.

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