Spray Atomization Study on Multi-Hole Nozzle for Direct Injection Gasoline Engines

We investigated the size of fuel spray droplets from nozzles for direct injection gasoline (DIG) engines. Our findings showed that the droplet size can be predicted by referencing the geometry of the nozzle. In a DIG engine, which is used as part of a system to reduce fuel consumption, the injector nozzle causes the fuel to spray directly into the combustion chamber. It is important that this fuel spray avoid adhesion to the chamber wall, so multi-hole injection nozzles are used to obtain spray shape adaptability. It is also important that spray droplets be finely atomized to achieve fast vaporization. We have developed a method to predict the atomization level of nozzles for fine atomization nozzle design. The multi-hole nozzle used in a typical DIG injector has a thin fuel passage upstream of the orifice hole. This thin passage affects the droplet size, and predicting the droplet size is quite difficult if using only the orifice diameter. We therefore fabricated several multi-hole nozzles with different thin passage areas and hole diameters. We evaluated the spray from the nozzles and determined the relationship between nozzle geometry, flow rate, and droplet size. We also evaluated the outlet velocity in the orifice holes and plotted the relationship between droplet size and velocity. We found that droplet size can be described by velocity and that the velocity has a correlation with the nozzle geometry. We also discuss how the thin passage geometry on the velocity makes it possible to predict droplet size from the nozzle geometry.