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Four-way catalyst system consisting of diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and lean NOx trap (LNT) with alternative combustion such as low temperature combustion (LTC) and premixed controlled compression ignition (PCCI) is one of the effective ways to achieve the US Tier 2 Bin 5 and future European emissions for light duty diesel vehicles. However, thermal responses such as substrate temperature and temperature gradient of each catalyst component in the exhaust treatment system are different under different combustion modes and operation conditions. One exhaust treatment component's performance or durability can not be sacrificed for the sake of another. In this paper, thermal management strategies for exhaust treatment component temperature and temperature gradient by controlling lean and rich conditions of low temperature combustions as well as premixed controlled combustion, EGR rate and exhaust flow are demonstrated on a Renault G9T600 engine.

A new diesel engine system adopting alternative combustion with rich and near rich combustion, and an airflow-dominant control system for precise combustion control was used with a 4-way catalyst system with LNT (lean NOx trap) to achieve Tier II Bin 5 on a 2.2L TDI diesel engine. The study included catalyst temperature control, NOx regeneration, desulfation, and PM oxidation with and without post injection. Using a mass-produced lean burn gasoline LNT with 60,000 mile equivalent aging, compliance to Tier II Bin 5 emissions was confirmed for the US06 and FTP75 test cycles with low NVH, minor fuel penalty and smooth transient operation.