Prediction of Oil Dilution by Post-injection in DPF Regeneration Mode 2019-01-2354
This work investigated the mechanism of oil dilution by post injection to remove accumulated particulate matter on the diesel particulate filter of diesel engines. We developed a model to simulate post injection spray under low ambient gas pressure conditions. The model can predict the quantity of fuel mass adhered on the cylinder wall. The adhered fuel enters oil sump through the piston ring and cause oil dilution. The fuel in diluted oil evaporates during normal engine operations. We focus on the mechanism of fuel evaporation from diluted oil. The effects of engine speed and oil temperature on the evaporation were investigated. The results showed that the fuel evaporation rate increases with increasing engine speed and oil temperature. Furthermore, we developed an empirical model to predict the fuel evaporation rate of diluted oil through regression analysis with measured data. The model was validated using two test engines at three constant speed conditions and two transient cycles. Oil dilution predicted by the model showed good agreements with measured data from gas chromatography. The effects of piston ring specifications on oil dilution were also experimentally investigated to clarify the significance of piston rings in the fuel transport model. The results revealed that there ring specifications have no effect on oil dilution regarding the engine used in this study. The coupling of the evaporation model and the post injection spray model provides a method for estimating oil dilution rate during engine operation with regeneration.