New strategies for soot emission reduction of HD vehicles

The reduction of particulate emissions limits requires new strategies for the tuning of engines and exhaust after treatment systems. A non-blocking exhaust after treatment solution for HD vehicles to achieve the EuroIV emission limits has been developed which consists of a platinum oxidation catalyst and a stainless steel deposition structure with open channels for continuous soot storage and oxidation [1]. The significant advantages compared to standard particulate filters are caused by the open channel structure and characterized by a relatively low level of back pressure, selective separation of soot (EC) and penetrability for engine lubrication oil incineration ash. Extensive laboratory studies, including a screening of numerous promising deposition structure designs, led to a metal catalyst structure with microsphere coating. The processes dominating particle deposition could be determined, leading to a target-oriented optimization of the deposition structure. Particle deposition caused by diffusion, interception and thermophoresis during instationary test conditions occurs. Measurements on the test bench with an EuroII HD engine show a gravimetric particulate matter reduction of 18 and 55 mg/kWh for the ESC/ETC, which is consistent with the laboratory-studies. A new photo acoustic instrument (PASS) was applied allowing reliable determination of soot deposition efficiency even during the transient test cycle (ETC) for modern HD engines with a low PM raw emission. Close correlation between number based (SMPS) and mass based (PASS, gravimetric) particle concentration measurements were observed. The exhaust aftertreatment system investigated here system provides a reliable solution yielding a conversion of up to 70% (ESC/ETC) for elemental carbon at a moderate back pressure.