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A light duty truck Renault Trafic with a naturally aspirated 2.5 l diesel engine was equipped with metal particulate filters of different sizes, installed at different positions along the exhaust pipe of the vehicle. The filters were operated on diesel fuel doped with a cerium based additive at concentration of 100 ppm in the fuel. Tests were carried out on chassis dynamometer using continuous repetition of the urban part of the European Driving Cycle as a « worst case » approach. Comparisons are made between the different sizes and positioning as regards both back-pressure build up and catalytic regeneration behavior. The results show that filter regeneration was always possible at continuous low speed driving, at relatively high filter back-pressure levels (i.e. high particulate accumulation in the filter), with an effect on fuel consumption.

Possible techniques to protect the filter against a failure scenario, so far reported, include filter by-passing and limiting the engine A/F ratio. Both techniques aim at controlling the oxygen content of the exhaust gas and thus reducing the oxidation rate in the filter. In this paper a new method for the protection of the trap is presented. This method, called Selective Flow Modulation (SFM) aims at controlling the reaction rate via the modulation of the exhaust gas flow through the filter. For the practical application of such a method, it is necessary to split the filter into at least two parts and to use at least one device for the flow modulation. In addition, a number of different possible SFM configurations are presented and their characteristics are analysed together with the experimental results of the technique applied on two engines, one heavy and one light duty.