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On September 1 st 2011, the Euro 5 + emission legislation will apply to passenger cars in Europe. It is characterized by the introduction of a new regulation concerning the number of soot particle emissions, whereas Euro5 legislation only applies to soot mass. This new regulation makes it necessary to investigate the impact of filter design on filtration efficiency as it pertains to particle number and to the Diesel Particulate Filter (DPF) operating window. This paper describes the investigation performed on a light duty test bench equipped with a Differential Mobility Spectrometer (DMS) which measures soot concentration number and soot particle size distribution in the exhaust gas effluent. Specific protocols were developed to be able to evaluate filtration efficiency in particle number when the DPF is empty of soot and also when the filter is soot loaded. Several DPF parameters such as filter length, filter diameter, cell geometry, and microstructure were studied.

As Diesel Particulate Filter (DPF) applications become widespread, the need for downsizing of filters increases. Indeed, downsizing allows reducing both filter and system costs, facilitates filter integration in the exhaust line close to the engine, and reduces overall system mass and potentially the precious metal loading. Filter downsizing is mainly limited by filter thermo-mechanical resistance because the system must be capable of storing enough soot before being forced to start filter regeneration in order to limit oil dilution and fuel consumption. The interval between two regenerations depends on filter maximum soot load (MSL) and volume. Thus, it is desired to increase filter MSL in order to keep long regeneration intervals with minimum filter volume. Moreover, in order to maintain acceptable backpressure on a loaded filter, it is required to use optimized cell geometries allowing significant pressure drop reductions.

Porous honeycombs filters have been widely used for diesel particulates filtration in passenger cars applications. In all current DPF applications, filter lifetime and design are dictated by the need to store non combustible ash generated at the exhaust. Therefore, improving the ash storage capacity of a filter appears as a major step towards the development of maintenance free DPF systems. This paper describes a new filter design that was developed to optimize ash storage volume. Numerical simulations and roller bench tests have been performed in order to compare the performances of this new filter to commercial honeycomb filters.