In coming years a special focus in the field of GDI engines will be on downsized concepts and highly-charged gasoline direct injection engines. This is due to stricter emission laws, higher customer requirements, greater environmental awareness as well as high demands on materials and resources. Especially at cold start, catalyst heating and warm up operation GDI engines have an issue with oil dilution. Fuel gets into the oil pan and is mixed with the engine oil so that the physical and chemical properties of the engine oil are changed. Adjusting engine operating points to higher mean effective pressures in downsizing concepts also an additional increase of the fuel input into the engine oil occurs.
At the University of Applied Sciences Regensburg measurements were carried out at a direct injected gasoline engine with lateral injector position. This engine with 1.8 l displacement disposes e.g. a common rail injection system up to 20 MPa, a variable camshaft regulation and a variable tumble system. For the following investigations a new measurement technique has been used that realizes the online analysis of the fuel quantity in the engine oil. In order to study the oil dilution mechanisms and the influence of different adjustment parameters investigations were carried out especially at engine operating conditions with high oil dilution risk. Besides the studies on steady-state operating points, it is possible to investigate transient engine operation referring to its issue on oil dilution.
Due to its high precision and low detection limit the used online measurement technique provides quantitative information about the fuel sorption and desorption rates at short measurement times. Defining a generic measurement procedure in order to receive a representative value of oil dilution for one specific engine operating parameter was the basic principle for further investigations. Operating parameters such as injection pressure and injection timing, charge motion, cooling temperature and different cam timings have been explored regarding their influence on oil dilution. Thus an optimized oil diluting calibration could be developed at each critical engine operation point.