Sensing the soot load in automotive diesel particulate filters by microwave methods

Modern vehicles with diesel engines need to be equipped with particulate filters (DPFs) to meet today's and tomorrow's stringent emission regulations. Such filters must be regenerated on a regular basis to burn off the soot adsorbed in the course of time. As the regeneration processes consume fuel, they must be kept to the bare minimum which requires a detailed knowledge of the actual soot load in the filter. We have investigated if the soot load can be determined in situ by the cavity perturbation method at operating frequencies in the low GHz range. We will show that, indeed, current microwave technology as used, for instance, in cellular phones is capable of detecting the soot load in a diesel particulate filter. Experimentally observed sensitivities of cavity resonance frequencies to soot load (adsorbed mass) were as high as 3 MHz g(-1). This contribution reports on the measurement approach, experimental results obtained in industrial dynamometer test benches and the conclusions to be drawn from the results.