Investigation of the effect of different structure parameters and operating factors on the integrated exhaust aftertreatment system for diesel engines and parameter importance analysis

Abstract

With diesel emission regulations growing more stringent, it is important to study the effect of different structure parameters and operating factors on the integrated aftertreatment system consisting of diesel oxidation catalyst (DOC), catalytic diesel particulate filter (CDPF) and selective catalytic reduction (SCR) during the design and optimization of the aftertreatment system. In this paper, a simulation model capable of exploring the interaction between the aftertreatment components was developed based on some relevant reaction mechanism, and the model accuracy was verified well using the experiment data. Then the effect of different parameters on the overall performance of the aftertreatment system was analyzed qualitatively. Finally, the importance score of each parameter was determined quantitatively based on Latin Hypercubic Sampling method and Random Forests algorithm. The results showed that larger diameter or larger cell density in DOC could improve the aftertreatment performance effectively. The increase in the wall thickness of each component had a negative impact on the aftertreatment system, except for CDPF wall thickness, which improved the filtration efficiency for particular matter (PM). When total aftertreatment length was fixed, high conversion efficiencies for carbon monoxide (CO) and total hydrocarbons (THC) were distributed in the region with large DOC length ratio, and NOx conversion efficiency was affected simultaneously by the length ratio of DOC, CDPF and SCR. An increase in CDPF length ratio and a decrease in DOC and SCR length ratios could contribute to the reduction of total pressure drop. Finally, Random Forests algorithm provided a good identification of the importance score of each parameter. DOC length and diameter played a dominant role in CO and THC conversion. The aftertreatment diameter had higher effect on NOx conversion efficiency than SCR length and PM filtration efficiency was mainly affected by DOC and CDPF length. Based on these qualitative and quantitative results, a design strategy for the integrated aftertreatment system was proposed, which provided some ideas for improving aftertreatment performance.