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Several previous SAE papers have discussed the direct on-line soot measurement device that uses radio frequency (RF) technology to measure filter soot loads in diesel particulate filters. This paper presents differential pressure measurement data from several different retrofit vehicle applications using various filter geometries. This data is discussed and correlated to laboratory test results. The durability of the system to urban buses is also outlined.

Filter regeneration systems require an accurate and reliable measurement of diesel particulate (soot) accumulation. This paper describes recent advances in the development of a device that uses radio-frequency (RF) technology to measure filter soot loads. A one-point calibration method is presented that provides a means to significantly reduce filter system development costs. Results from both on-vehicle and laboratory testing programs are discussed. The on-line monitoring of catalytic and energy-addition regeneration processes is also described.

Control of the diesel particulate filter regeneration process requires a reliable and accurate on-line measurement of the amount of carbon particulates or soot accumulated in the filter. Both RF- and back-pressure-based measurement methods have been developed for this purpose. Under lowload conditions, the collection of condensed organic material can adversely affect the accuracy of back-pressure-based measurements. Experiments described here illustrate that the RF-based measurement method gives a direct measurement of filter soot load, which, is independent of exhaust gas flow conditions and condensed organic material.

A new method of measuring diesel-particulate accumulation has been developed that uses electromagnetic energy to interrogate a ceramic filter and to give a real-time measurement of the trapped-soot level. The measurement method is inherently independent of engine-exhaust-gas volumetric flow rates and is relatively insensitive to changes in filter temperature. This paper presents laboratory data, derived from testing of full-scale, wall-flow filter systems, demostrating the viability of the measurement method. The implementation of the measurement method in on-vehicle regeneration system is also discussed.

Control and location of the energy input to a ceramic diesel filter is essential for successful filter regeneration. External heat sources, such as burners or resistance heaters, initiate soot combustion at the inlet face of the filter, and complete regeneration depends on the combustion front propagating throughout the filter. Uneven or uncontrolled soot combustion can cause incomplete filter regeneration and/or filter destruction. In contrast, it is possible to provide a more uniform energy input to a filter by incorporating microwave-susceptible materials in the filter body and then using RF (microwave) energy to initiate combustion. This method gives improved control over the soot combustion and lower thermal stresses within the filter. This paper discusses the RF engineering and materials considerations involved in RF-based regeneration of wall-flow and ceramic-foam diesel filters.