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1 Although combustion system improvements allow extremely low level of particulate (EURO 4 particulate level is already achieved) the particulate filter appears to be the only solution to reduce solid particulate emission by two to three order of magnitude over the whole size range starting from 10 nm. This is the reason why an active particulate filter system has been developed. The major issue was to fill in the gap between particulate regeneration temperature (550°C) and the naturally low exhaust gas temperature of modern DI diesel engine (150°C to 200°C in city driving conditions). This low exhaust gas temperature is the result of overall efficiency improvement to reduce fuel consumption.

A new criterion to assess diesel fuels has been developed at the Institut Français du Pétrole, in collaboration with PEUGEOT and RENAULT. It is a comparative method which makes it possible to assign a Particulate Number (PN) to a diesel fuel, calibrated, as for the cetane number, with two reference fuels specially formulated. One has a low emission level, the other one a very high level. Values PN=0 and PN=100 are respectively attributed to each of them. The first is made up of tetradecane, and the second of a highly aromatic mixture containing 55 % tetradecane, 40 % 1-methyl-naphthalene and 5 % phenanthrene. The PN value of a diesel fuel derives from measurements of particulate emissions of an engine successively fuelled with the three products (CPP) and from a simple analysis in laboratory of the nitrogen content (N) of the tested fuel.