Performance of Catalyzed Particulate Filters without Upstream Oxidation Catalyst

The possibility to employ a single-brick system with a catalyzed filter (CDPF) for the after-treatment of diesel engines is potentially a promising and cost-effective solution. In the first part of this paper, the effectiveness of a single brick CDPF system towards reducing the gaseous CO and HC emissions is investigated experimentally and computationally. The second part of the paper deals with the behavior of single brick catalyzed filters compared with two brick systems comprising an upstream oxidation catalyst. The main differences of the two systems are highlighted in terms of regeneration efficiency and thermal loading, based on simulation results. The modeling work is based on a 3-dimensional model of the catalyzed filter and an axi-symmetric model of the oxidation catalyst. Model validations are presented based on engine bench testing. The simulation results indicate that in the case of a “controlled” regeneration with prolonged post-injection the single brick system exhibits a higher regeneration efficiency compared to the DOC+CDPF system. This is accompanied by higher filter temperatures, which, nevertheless, remain below the critical limits for filter damage. In the case of an “uncontrolled” regeneration with short post-injection period, the single brick system initially exhibits a local temperature peak near the center of the filter due to the combined effect of exhaust CO, HC oxidation and soot combustion. Although the distribution of soot and the temperature fields are different compared to the DOC+CDPF systems, the maximum temperatures differ by less than 100°C between the two systems.