Combined NO{sub}x and PM exhaust gas aftertreatment approaches for HSDI diesel engines

摘要

While particulate filters are already being used in increasing numbers with production HSDI (High Speed Direct Injection) diesel powertrains, combined NO{sub}x and PM reducing devices are still in the development phase. In the past, various lean NO{sub}x trap (LNT) applications using internal and external measures to enable enrichment of stoichiometric exhaust gas have been investigated. Some initial results on the integration of LNT and catalytic Diesel Particulate Filter (cDPF) functionality into HSDI powertrains have already been published, and systems consisting of a cDPF and LNT on separate bricks as well as one brick solutions have been described without being directly compared. In the present paper a system comparison of various exhaust gas aftertreatment system architectures in combination with a prototype engine designed to fulfill future emissions legislation at lowest CO{sub}2 levels performed at AVL is described. Location of the LNT both up- and downstream of the cDPF and the performance of a single brick 4-Way Catalyst (4-WC) were investigated. With selected exhaust gas aftertreatment devices, fuel enrichment has been assessed using three different approaches: Internal rich combustion, external fuel injection (exhaust port) and fuel evaporation upstream of the exhaust aftertreatment device. Prototype fuel injection devices have been set up to demonstrate the advantages and disadvantages for production application. The main focus of the investigations of the different systems was their impact on NO{sub}x conversion efficiency, desulphurization and cDPF regeneration capability. Furthermore, the interaction of the cDPF and LNT and their performance under lean and lean/rich conditions were investigated. Finally, a detailed assessment of the compared systems was performed and a possible combination of NO{sub}x and PM reduction device with alternative combustion was considered.