PM effects on health are believed to be more related to particle total number rather than to particle total mass. This gave rise in Europe to the forthcoming introduction of an emission standard on total particle number, that will take place for passenger cars from EURO5 (stage b) on. The behavior of the DPF is therefore under investigation, to better understand its effectiveness toward particle number reduction. Moving from that background, a study on the effect of a close coupled DOC-CDPF (Diesel Oxidation Catalyst + Catalyzed Diesel Particulate Filter) on PM emissions is proposed in this paper, with special focus on the comparison between mass and number collection efficiency. Experimental data have been gathered at the engine laboratory of the University of Rome Tor Vergata, equipped with a FIAT 2.0l EURO 5 passenger car engine. Data have been acquired with a TSI 3090 EEPS to measure particle distribution and total number, and an AVL-415 S to measure PM mass emissions. A numerical code has been also developed to represent the DPF behavior, in terms of soot load (g/l) trend, under forced regenerating operating conditions and better understand regeneration potential as a function of time. Results, acquired for three non regenerating and one forced regenerating modes, prove that mass and number efficiencies are close to 100%, with a slight decrease during the forced regeneration mode.

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