Fuel Property Effects on Spray Atomization Process in Gasoline Direct Injection

This paper presents a computational fluid dynamics (CFD) study of the Engine Combustion Network (ECN) Spray G under non-vaporizing condition, focusing on the impacts of fuel properties as well as realistic geometry on the atomization process. The large-eddy-simulation method, coupled with the volume-of-fluid method, is used to model the high-speed turbulent two-phase flow. A moving-needle boundary condition is applied to capture the internal flow boundary condition accurately. The injector geometry was measured with micron-level resolution using x-ray tomographic imaging at the Advanced Photon Source at Argonne National Laboratory, providing detailed machining tolerance and defects from manufacturing and a realistic rough surface. A 2.5-μm fine mesh is used to sufficiently resolve the details of liquid-gas interface and the breakup process. The fuel properties, i.e., density, dynamic viscosity and surface tension, are investigated by comparing three fuels, iso-octane, ethanol and E30 (70% iso-octane and 30% ethanol blend by volume) in the spray simulation. It is shown that the iso-octane spray has 12% higher injection velocity and 5% lower mass flow rate at hole exit compared to ethanol due to fuel effects. Detailed analysis of spray morphology, detached ratio and SMD shows that the fuel property effects are insignificant at this cold condition, while the impacts of in-nozzle geometry details as reported in previous study are applicable to different fuels and are generally more profound compared to the fuel impacts.