Investigations on PN formation and emission from passenger car GDI engines

To meet the future CO2 limits, several engine manufactures increase their proportion of gasoline engines equipped with direct injection systems (GDI). However particle number emissions of GDI engines is much higher than of port fuel injection (PFI) engines. Reasons for particle emissions are nonhomogeneous mixture formation, the presence of local rich zones and liquid fuel in the combustion chamber [1; 2]. Downsizing and Downspeeding are promising solutions to reduce the fuel consumption. In context with the new emissions regulations the reduction of particle number emissions at high engine loads is becoming increasingly important. The higher engine loads at lower engine speeds lead to more fuel injection in a lower in-cylinder charge motion environment. Both are negative for the mixture formation and the evaporation of the liquid fuel.

In previous work, a single cylinder research engine was operated to measure the particle number emissions at high engine loads [3]. In this work, a CFD-Model was used to analyze the mixture formation process. Therefore, a cold simulation was performed up to the point of ignition. The CFD simulations provide an insight into the mixture formation process, the fuel evaporation process and the creation of liquid film in the combustion chamber. ... mehrThe simulations are performed at boundary conditions of the experimental work and are thus directly comparable to the measurements. To validate the simulations, optical in-cylinder measurements were done at the same operation points. The focus is on high engine loads with an IMEP of 1.4 MPa and an engine speed of 2000 rpm. The variation in this paper will be Start of injection (SOI) for two different injectors with different injection pressure and charge motion variations. At the end a short summary about the overall project results is given.