Highly integrated exhaust gas aftertreatment systems in heavy-duty applications

The application of highly integrated exhaust aftertreatment systems like SCR-coated Diesel Particulate Filters (SDPF) allows both a reduction of required package space and functional advantages [1] like a further reduction of tailpipe emissions compared to conventional systems. In particular for engine cold start, earlier AdBlue/DEF dosing and thus reduced tailpipe emissions can be achieved by improving system heat-up through bringing SCR functionality further upstream within the exhaust aftertreatment system [2].In this report specific interactions resulting from integration of multiple functionalities on a single system component are investigated in detail and discussed regarding system aspects. One key trade-off arises from competing chemical reaction mechanisms involving nitrogen dioxide which is consumed on the same component by passive soot oxidation on the one hand and the fast SCR reaction on the other, the latter being significantly favoured due to faster reaction kinetics [3].As a consequence, it is shown that the passive regeneration capability of the accumulated soot is seriously inhibited with increasing SCR efficiency. A safe and stable passive regeneration can solely be achieved for applications running on high engine loads.Means by which this fundamental trade-off between safe filter regeneration and high NO_x reduction rates can be handled for future heavy duty diesel applications, optimized operation strategies and advanced system configuration, are identified.