Experimental and Modeling Results Comparing Two Diesel Oxidation Catalyst - Catalyzed Particulate Filter Systems

Steady-state particulate loading experiments were conducted on an advanced production catalyzed particulate filter (CPF), both with and without a diesel oxidation catalyst (DOC). A heavy-duty diesel engine was used for this study with the experiments conducted at 20, 40, 60 and 75 % of full load (1120 Nm) at rated speed (2100 rpm). The data obtained from these experiments were used and are necessary for calibrating the MTU 1-D 2-Layer CPF model. These experimental and modeling results were compared to previous research conducted at MTU that used the same engine but an earlier development version of the combination of DOC and CPF. The motivation for the comparison of the two systems was to determine whether the reformulated production catalysts performed as good or better than the early development catalysts.

The results were compared to understand the filtration and oxidation differences between the two DOC+CPF and the CPF-only aftertreatment systems. Comparisons of the pressure drop, filtration and passive oxidation performances are presented. Differences in the two aftertreatment system performance were minimal. For both systems it was observed that NO₂ PM oxidation is the dominate oxidation mechanism for exhaust temperatures below 400°C. DOC oxidation of NO to NO₂ for both DOC's was similar with the highest conversion efficiencies observed at the two lower loads corresponding to the temperature range of 280 - 340°C. This is comparable to ranges observed in other studies. Conversion of NO to NO₂ across CPF in CPF-only configuration was 10 to 28% higher in the earlier development version compared to the production catalyst resulting in higher NO₂ outlet concentrations.