Injector Selection And Matching Technology For GDI Engine Using Spray Laser Diagnose And Simulation Methods

Comparing to traditional port fuel injection（PFI） engines, gasoline directinjection（GDI） engines have obvious advantages on fuel economy，WOT torque，and cold start. Consequently，GDI technology becomes a inevitable tendency in thegasoline engine field. However, some drawbacks for GDI engines including the sprayimpingement upon the piston and cylinder wall accompanied with uneven gas mixturedistribution, which would lead to lubricant dilution, fuel economy deterioration andincreasing emissions. Matching among spray characteristics, combustion chambergeometry and in cylinder air flow field with different injectors has to be investigatedand optimized to select a suitable one for a special GDI engine.CFD simulation has been widely used to conduct combustion system design andoptimization because of its benefits on time and costs. It’s very necessary to match asuitable injector for a GDI engine to decrease wall fuel and optimize the gas mixturedistribution by using CFD method. However，there isn’t a system research on thissubject. In this paper, the spray characteristics consisting of penetration、spray patternand droplet size for a multi-hole and an outward-opening GDI injector were preciselymeasured and investigated with transient white light illumination、LIF and PDI laserdiagnostics technologies. A spray simulation model was built with the commercialCFD software AVL FIRE, and further calibrated and validated using the experimentaldata. Furthermore, the spray model was embedded in the3D dynamic grid of aturbocharged GDI engine to simulate and study the spray and air-fuel mixtureformation process. Finally, a more suitable injector was selected to match the specialGDI engine by the thorough comparison.Due to the researches in this paper, the following conclusions can be drawn:1．The precise and reliable spray simulation model has been obtained aftercarefully calibrated using the measured data for the penetration, cross-surface patterndistribution and droplet size distribution； 2．The turbocharged GDI engine addressed in this thesis has serious sprayimpingement and uneven air-fuel mixture distribution at low speed full load operatingcondition；3．Retarding the injection timing can reduce the spray impingement quantityusing single injection strategy, but lead to decreasing homogeneity of air-fuel mixture;4．Dual-injection injection strategy can obviously reduce fuel impingement, butthe homogeneity of the mixture will decrease with delaying second injection timing;5．Compared to six-hole injector spray simulation，10%increment of fuelevaporation directly and8%decrement of mix wall fuel were obtained usingoutward-opening injector，meanwhile，there is an approximate equal accumulated wallfuel mass for the two injectors. Therefore, outward-opening injector is superior tosix-hole injector to match the special GDI engine.