Assessment of the Influence of GDI Injection System Parameters on Soot Emission and Combustion Stability through a Numerical and Experimental Approach

The next steps of the current European and US legislation, EURO 6c and LEV III, and the incoming new test cycles will impose more severe restrictions on pollutant emissions for Gasoline Direct Injection (GDI) engines. In particular, soot emission limits will represent a challenge for the development of this kind of engine concept, if injection and after-treatment systems costs are to be minimized at the same time. The paper illustrates the results obtained by means of a numerical and experimental approach, in terms of soot emissions and combustion stability assessment and control, especially during catalyst-heating conditions, where the main soot quantity in the test cycle is produced. A number of injector configurations has been designed by means of a CAD geometrical analysis, considering the main effects of the spray target on wall impingement. The numerical CFD simulation has helped the definition of the injection system and of its control settings for a given operating condition, in terms of start of injection, injection pressure and number of pulses per stroke. Engine test bench experiments have finally been used to validate the numerical results, and to further optimize the injection system calibration in order to minimize soot emissions, while respecting combustion stability constraints. The main results are presented in the paper.