Effects of DOC and CDPF Catalyst Composition on Emission Characteristics of Light-Duty Diesel Engine with DOC + CDPF + SCR System 2018-01-0337

With regulatory standards for diesel engine emissions becoming stricter worldwide, integrated catalytic systems are becoming increasingly necessary. One of the better approaches is to use an after-treatment system consisting of a diesel oxidation catalyst (DOC), a catalyzed diesel particulate filter (CDPF), and a selective catalytic reduction (SCR), but many factors can affect how well this system works. This study investigates the effects of DOC and CDPF catalyst composition on emissions characteristics for DOC + CDPF + SCR systems by collecting reactor and engine data. The reactor results show that the light-off temperatures (T₅₀) of CO and C₃H₆ increase with the growth of Pt:Pd ratio while the T₅₀ of NO degrades. An engine dynamometer test was conducted on a light-duty diesel engine equipped with DOC + CDPF + SCR. The results show light-off curves of CO and THC that are smoother than the reactor data. The CO and THC oxidation activities increase monotonically as the Pt:Pd ratio decreases in a low-temperature range (≤ 400 °C), whereas NO oxidation exhibited the opposite trend. But the beneficial effect from Pt or Pd degrades with increases in temperature (> 400 °C). Moreover, the differences in the light-off characteristics caused by Pt:Pd ratio changes in DOC, are less affected by the CDPF catalyst and can be maintained after CDPF. High Pt content in CDPF causes a greater reduction in the nuclei-mode particles but has little impact on the accumulation-mode. The particulate number-size distribution shows bimodal or multimodal lognormal distribution after CDPF. The reductions of the particulate number and the particulate mass are more than 90% and show a downward trend with the increase of space velocity. Compared to DOC, improving Pt level in CDPF is more conducive to SCR reduction. Besides, no significant influence of DOC or CDPF catalyst composition on back pressure and engine economic performance has been found.