RF Studies of Soot and Ammonia Loadings on a Combined Particulate Filter and SCR Catalyst

Abstract

Modern diesels employ a particulate filter (DPF) to reduce soot emissions. Additionally, the selective catalytic reduction (SCR) of NOx by NH3 stored on the SCR catalyst reduces NOx emissions. In some vehicles the functions of these aftertreatment components are combined in the SDPF, a DPF having a SCR washcoat. The RF resonant method has been shown to be an alternative tool for measuring the DPF's soot loading and the SCR's NH3 loading. For both applications, the transmitted electromagnetic signal between antennae placed on either side of the catalyst change with loading. Here we report the influence of the RF signal on both soot and NH3 loadings on a SDPF segment. We show that the attenuation of the RF signal by soot is much larger than that caused by saturating it with 400 ppm NH3. By taking the mean RF signal amplitude measured over a wide range of frequencies, we demonstrate a method for determination of the soot loading even in the presence of stored NH3. For "light" soot loadings, before the RF attenuation by soot cause the resonant modes to disappear in the spectra, we demonstrate a method for the simultaneous determination of both the soot and NH3 loadings.