Abstract
An experimental work has been made to study the spray structure and characteristics of high-pressure swirl-type injectors for gasoline direct injection (GDI) engines. The spray has been lighted both along its axis and in cross sections perpendicular to it by a pulsed light sheet, 100 Ým thickness and 12 ns in duration, produced by a Nd-YAG laser. Spray images have been captured by a CCD camera with a frame grabber synchronized with the laser pulse and the injection command. A digital image processing system has provided analyzing the collected images.
The transient spray time- and space-evolution has been studied under different operative conditions as a function of the time after the start of injection (SOI). The spray structures and the effects of fuel injection pressure, ambient pressure and injector design have been analyzed in details. The fuel has been injected at pressures of 5.0, 7.0 and 9.0 MPa by electronically controlled injectors in an optically accessible vessel with backpressure ranging between 0.1 to 1.2 MPa. A detailed spatial and temporal characterization of the emerging spray has been carried out showing interesting peculiarity of the jet for the different operative conditions.
The global parameters of the spray in terms of tip penetration, cone angle and hollow-cone structure have been reported. Finally a comparison between 60¢X and 80¢X nominal spray-cone angle injectors has been carried out.
The ambient pressure strongly affects the spray structures resulting a spray isotropic contraction and a less evident development of small droplets and vortexes zones at higher backpressure values. Varying the injection pressure the global spray structures is quite similar except for the spray tip penetration, which increases as the injection pressure increases.
The initial phase of the spray and the morphology of the hollow-cone structure depend markedly on the injector type.