Development of Valve Train Configurations Optimized for Cold Start and their Effect on Diesel Soot Emission

The continuous pursuit of more efficient diesel engines and the stricter emission regulations with the introduction of the Real Driving Emissions test (RDE) necessitate further investigations of heating strategies and their suitability in terms of series production. Under these circumstances heating strategies of a variable valve train for a single-cylinder research diesel engine have been first simulated and then experimentally tested at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology (KIT). By combining statistical experimental design (DoE) and 1-D gas exchange simulations, empirical DoE models for the design of suitable camshaft configurations have been established. After having performed a potential assessment, the most favorable configurations were manufactured and subsequently tested. The configuration with an additional opening of an outlet valve during the intake stroke (2nd Event) shows the best compromise between engine out HC/CO emissions and an efficient exhaust gas temperature increase. The strategy-related state changes in the combustion chamber when using a 2nd Event and the resulting soot characteristics, in terms of size and distribution, resulting reactivity and filter soot number, are subject of the second research phase. For the exact characterization of the resulting soot and for the detailed base collation, the size distribution and the soot reactivity were further investigated - in addition to the number of soot particles. In the context of these investigations, the internal engine soot formation and oxidation processes were analyzed by means of the extended two-color pyrometry. The final results of the direct comparison of the individual camshaft configurations help to make a statement at an early stage of the development process as to whether the effects of the heating strategy harmonize with the present aftertreatment system or need to be adapted to the new soot reactivity.