Comparative Study to Assess the Soot Reduction Potential of Different In-Cylinder Methods and Exhaust Gas Aftertreatment Systems for Direct Injection Diesel Engines

In this study different methods to reduce the soot emissions of Diesel engines were investigated and compared to obtain their soot reduction potential. Apart from investigations on the practically usable engine map area with so called homogeneous charge compression ignition (HCCI) combustion processes a new heterogeneous combustion processes was developed and investigated which offers significantly reduced soot emissions while still applicable in the entire engine map. For the HCCI experiments the emphasis was put on the achievable engine load range when using conventional injector nozzles which still allow a conventional heterogeneous engine operation. The newly developed heterogeneous combustion process is mainly characterized by an injection strategy which separates the different part injections not only temporally but also spatially and therefore on the one hand reduces the soot formation during the early stages of the combustion and on the other hand increases the soot oxidation later during the combustion. In addition to these investigations of the soot reduction potential of advanced in-cylinder methods a newly designed modular particulate filter system with an electrical regeneration strategy was tested, which enables a filter regeneration independent of additional engine measures with almost no impact on the fuel consumption regarding the energy amount necessary for the filter regeneration.

The comparison of these different measures for reduced soot emissions has revealed that in-cylinder measures with reduced raw emissions are important and effective, but a complete soot reduction by means of the maximum achievable filtration efficiency of a particulate filter is still only possible with a particulate filter system. For the impact of the different measures on the fuel economy to achieve these very-low soot emissions today still the regeneration strategy of the particulate trap plays the key role.