Study of the Benefits and Drawbacks of a Substantial Increase of Rail-Pressure in GDI-Injector Assemblies

In the present paper are examined the consequences of a substantial rise in the injection pressure for Gasoline Direct Injection (GDI) injector assemblies. The paper presents a comparative study of the spray behavior of two different injector nozzle layouts submitted to current 10 Mpa rail-pressure as well as to a 30 Mpa injection pressure. To evaluate the differences in the fundamental physical spray parameters are used several specially developed optical visualization techniques, which enable phase-Doppler, PIV, Laser-sheet and high-speed recordings of dense high pressure fuel sprays. A recently developed injector actuator and the necessary modifications to existing high-pressure pumps to reach a 30 MPa pressure level in the fuel system are presented. The change in basic spray parameters (time-resolved droplet distribution and spray momentum) caused by the rail-pressure rise is examined. Furthermore the impact on the combustion behavior is studied with a 3D-numerical simulation code NCF-3D as well as on a fired GDI-engine test bed. The paper concludes with a discussion of the degree of improvement, which can be expected for a GDI lean-burn system layout, when a 30 MPa rail-pressure is applied. Finally the production costs and complexity of new higher performance components are compared to the possible improvement their introduction can offer.