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The regeneration of a Diesel Particulate Filter (DPF) is dependent on both the amount and type of soot present on the filter. The objective of this work is to understand how the fuel can affect this ease with which soot can be oxidized. This soot was produced in a two-cylinder four-stroke direct-injection diesel engine, operated with a matrix of fuels with varying aromatic and sulphur level. Their oxidation behaviour in different environments was determined by Temperature Programmed Oxidation in TGA and a six-flow reactor. Transmission electron microscopy was used to examine the soot morphology. Oxidation with only O2 shows oxidation temperatures strongly dependent on the fuel type. Soot oxidation in the presence of NO and a Pt-catalyst results in a lower oxidation temperature. SO2 has an inhibiting effect leading to higher soot oxidation temperature.

A catalytic deSoot-deNOx system, comprising Pt and Ce fuel additives, a Pt impregnated wall-flow monolith soot filter and a vanadia-type monolithic NH3 - SCR catalyst, was tested with a 2 cylinder DI diesel engine. The soot removal efficiency of the filter was 98-99% (mass), the balance temperature (stationary pressure drop) was 315 °C at an engine load of 55%. The NOx-emission at high loads is around 15% lower than those of engine running without fuel additives. The NOx conversion ranged from 40 to 73%, at a NH3/NOx ratio of 0.9, both measured at a GHSV of 52,000 l/l/h. The maximum NOx conversion was obtained at 400 °C. No deactivation was observed after 380 h time on stream.

The physical state of a heterogeneous soot oxidation catalyst has a big impact on their performance. Contact between soot and solid catalysts is one of the key parameters for soot oxidation. Catalyst formulations based on low eutectic melting points were studied. Formulation based on cesiumsulfate and vanadiumoxide, became active at their melting point of 320-350 °C. Ceramic foam can act as support for the liquid catalyst as well as a deep filter for the soot. Downstream of a small diesel engine a balance temperature of 350 °C was established with an initial trapping efficiency of 40 %. Stable pressure drop over the system was maintained over a period of more than 24 hours.

The Scanning Mobility Particle Sizer (SMPS) and the Electrical Low-Pressure Impactor (ELPI) are frequently used to measure the number and size of combustion aerosols. The instruments are especially popular in the field of engine technology, where the emission of “particulate matter” is restricted by legislation. During the experiment with a “standard” ELPI it is observed that initially the number of small particles decreases rapidly, while simultaneously the number of larger particles increases. This non-ideal behavior of the ELPI can be overcome by the usage of oil-soaked sintered impactor stages. The interpretation of the results as measured by SMPS and ELPI is not straightforward due to the fractal character of the diesel soot agglomerates. The theory of fractal-like agglomerates is used to assess the performance of the ELPI and the SMPS for the measurement of diesel soot particles and is validated visually with electron microscopy (SEM).