Computations of Hollow-Cone Sprays from a Pressure-Swirl Injector

A computational model is proposed and analysis is carried out to study the atomization processes of hollow-cone fuel sprays from pressure-swirl injectors for a Gasoline Direct-Injection (GDI) Spark Ignition (SI) engine. The flow field inside a swirl injector is numerically analyzed, and characteristics of the liquid sheet at the nozzle exit are predicted. The intact length (i.e., breakup length) of the sheet is calculated from a semi-empirical correlation and a Sauter Mean Diameter (SMD) at the breakup location is estimated based on the classical wave instability theory. The spray dynamics that address the interactions between liquid drops and surrounding gas phase are simulated using FIRE code with modified spray models. The objective is to understand the effects of nozzle geometry and engine operating conditions on spray characteristics so that the spray structure can be optimized through the injector design to meet the fundamental requirements of GDI engines.

Experimental measurements are performed to provide the global spray images, drop size distribution, and mean particle size (i.e., SMD). Computed and measured spray characteristics, such as spray width, cone angle, and tip penetration, are compared, and good levels of agreement are achieved. The results show that spray width and penetration decrease significantly as the ambient pressure increases. However, they are relatively insensitive to the injection pressures evaluated.