Abstract
In order to meet the stringent Euro6 PN emission targets, it is important to understand the mechanism of the soot formation. Generally speaking, soot generates from combustion that occurs under overly rich air/fuel mixtures commonly due to poor air utilization or piston wetting. For gasoline direct injection (GDI) engines, in particular, fuel rich zones near injector tip due to fuel wetting has been identified as an additional source. The mechanism for fuel injector tip wetting is tightly coupled to the engine operating conditions, injector hole design, and needle motion dynamics. Over time, the fuel adhering to the injector can lead to degraded spray quality from deposit accumulation subsequently resulting in coking of the injector flow passages. In this study, an analysis based approach is presented to understand the injector tip wetting phenomenon along with near nozzle flow structure. The analysis is based on CFD of the internal nozzle flow using the Homogeneous Relaxation Model (HRM) approach for two injector designs considering the effect of stepped-hole and injector seat thickness.