2017 年 12 巻 1 号 p. JFST0012
We investigated atomized spray droplet size from multi-hole nozzles for direct injection gasoline (DIG) engines. Our findings showed that the droplet size can be described by the nozzle-hole geometry. For the DIG engine, adequate spray pattern and finely atomized spray are important to achieve low emission or/and low fuel consumption. As an injector for DIG engines, multiple holes (multi-hole) type nozzle is typically used because of adaptability of spray pattern. The multi-hole type spray has been generally used for Diesel engines, and the characteristics have been investigated in earlier studies. However, multi-hole nozzles for DIG engines require narrow spacing as fuel passage just upstream of the orifice hole. The narrow fuel passage affects spray characteristics including droplet size. This makes droplet size prediction and designing orifice geometry difficult, thus the narrow passage geometry needs to be incorporated as a design parameter. We therefore investigated relation between droplet size and nozzle geometry both experimentally and theoretically. Experimentally, we evaluated an experimental dataset which was done in previous work in which the spray droplet size from the fabricated test sample nozzles, and determined the relationship parameters between nozzle geometries, flow rate, and droplet size. The experimental result in which its pressure range was 1 to 15MPa showed that velocity at outlet of orifice-hole is a dominant factor to determine droplet size, and that the velocity has a correlation with the nozzle geometry. Theoretically, we focused on a pressure-drop at the narrow passage, which can describe velocity at the outlet of the orifice-hole. Finally, theoretical approach described the droplet size by using the orifice geometries incorporating the parameter of narrow passage.
