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Diesel fuel spray characteristics are thought to depend on cavitation inside the fuel injector nozzles. These nozzles are very small and the fuel flow is very fast, making experimental observation very difficult. Numerical simulation of the two-phase flow is hindered by the severe density difference between the liquid and vapor as well as the existence of complex free surfaces. Recent experimental and numerical advances are now permitting visual observation of real-scale cavitating flow and two-dimensional simulation of the cavitating flow. In contrast to past work, we have chosen to study asymmetric nozzle flow. Asymmetry is more representative of real injector geometry than symmetric nozzles and may yield more reproducible results. Experimental runs of 1 mm long nozzles were made at upstream pressures up to 120 bar with downstream pressures from 1 to 50 bar. Photographs of planar asymmetric nozzles revealed complex transient structures on the fuel-vapor interface.

The flow through diesel fuel injector nozzles is important because of the effects on the spray and the atomization process. Modeling this nozzle flow is complicated by the presence of cavitation inside the nozzles. This investigation uses a two-dimensional, two-phase, transient model of cavitating nozzle flow to observe the individual effects of several nozzle parameters. The injection pressure is varied, as well as several geometric parameters. Results are presented for a range of rounded inlets, from r/D of 1/40 to 1/4. Similarly, results for a range of L/D from 2 to 8 are presented. Finally, the angle of the corner is varied from 50° to 150°. An axisymmetric injector tip is also simulated in order to observe the effects of upstream geometry on the nozzle flow. The injector tip calculations show that the upstream geometry has a small influence on the nozzle flow. The results demonstrate the model's ability to predict cavitating nozzle flow in several different geometries.

Time resolved measurements of non-evaporating, non-burning fuel sprays injected into a quiescent atmosphere were performed. The experimental parameters included ambient gas density, mass of fuel injected per stroke, pump speed, and nozzle diameter. High speed films of fuel sprays were obtained using a rapidly pulsed Cu-vapor laser in synchronization with a high frame rate film camera. The laser light intensity transmitted through the spray was recorded directly by the film camera. The information encoded on the film was subsequently digitized using a projector/CCD camera system. Finally, instantaneous ensemble averaged properties of droplets constituting the spray were estimated by quantitative analysis of the digitized transmission images. These measured properties included the Sauter mean diameter (SMD) averaged over the entire spray or over a given cross-section. In addition, the images yielded other spray parameters such as tip penetration, cone angle, and injection duration.

Because combustion in direct injection engines is strongly influenced by the details of the fuel spray in these engines, we have begun a broad research effort of jet breakup experiments and modelling of these high pressure sprays. The main objective of this effort is to better understand fuel injection from the study of the spray-jet breakup process and the associated fuel-oxidant mixing. The focus of this paper is the development of specific models for atomization of the spray-jet. These models are then compared to each other and to preliminary data from the spray-jet breakup experiments. Initial results indicate that KIVA with this proposed spray model shows good agreement with low pressure data (69 MPa) but underestimates spray penetration for higher pressures (104 MPa).