GDI injection systems have become dominant in passenger cars due to their flexibility in managing and advantages in the fuel economy. With the increasingly stringent emissions regulations and concurrent requirements for enhanced engine thermal efficiency, a comprehensive characterization of the fuel spray behavior has become essential. Different engine loads produce in a variety of fuel supplying conditions that affect the air/fuel mixture preparation and influence the efficiency and pollutant production. The flash boiling is a particular state that occurs for peculiar thermodynamic conditions of the engine. It could strongly influence the mixture in sub-atmospheric environments with detrimental effects on emissions. In order to obtain an in-depth understanding of the flash boiling phenomena, it is necessary to study the parameters influencing the mixture formation and their appearance in diverse engine conditions.
The objective of this study is to investigate the effect of the ambient pressure and temperature on the morphology of a multi-jet spray operating in flash boiling status using a Gasoline Direct Injection setup. An eight-hole, GDI injector from the Engine Combustion Network (ECN), was investigated under flashing and non-flashing conditions. The experiments were performed in an optically-accessible, constant-volume vessel at engine-like conditions. A hybrid optical setup, Z-type schlieren and Mie scattering, using a high-speed C-Mos camera allowed the quasi-simultaneous acquisition of both the vapor and the liquid phases. A customized image-processing procedure, developed in Matlab environment, was used to outline the contours of both the fuel phases. Different morphologies of the fuel spray were studied as function of the injection pressure, the fuel temperature, and the backpressure in the vessel, through the measurement of the axial penetration and cone angle.