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Particulate emissions from diesel engines mainly consist of soot and high-boiling hydrocarbons (volatile fraction). To reduce the volatile fraction different precious metals and their combinations are tested in traps and supports especially at low loads. A sufficient catalyst's efficiency at low exhaust-gas temperatures (low load) requires a large active catalyst surface. Due to the soot in the diesel exhaust-gas, the catalyst can be covered by a soot layer reducing the catalyst's efficiency. The accumulated soot in the trap must be oxidized. Nonprecious metal catalysts are able to lower the soot ignition temperature. The reduction in ignition temperature depends on the catalyst material used. The influence of the catalyst's concentration and the use of an additional washcoat are also investigated.

This paper presents the results of experimental and theoretical investigations on measuring particulate emissions of diesel engines in a dilution tunnel. The results offer a contribution to understanding the influence of several parameters on the particle phase of exhaust gas when diluted and mixed with air. These parameters include the exhaust gas temperature, the dilution ratio of the exhaust gas in the air, the mixture temperature, the flow and mixture conditions, the amount of filter loading and the filter material. In order to determine which physical/chemical processes dominate particle formation in diluted exhaust gas, the results of calculations in terms of condensation and adsorption are compared with the experimental findings. An increase in measured particulate concentrations is generally favoured by short sampling times, fast mixing processes, high exhaust gas temperatures, low mixture temperatures and low dilution ratios.