Technique for Analyzing Swirl Injectors of Direct-Injection Gasoline Engines

This paper describes the numerical and experimental approaches that were applied to study swirl injectors that are widely used in direct-injection gasoline engines. As the numerical approach, the fuel and air flow inside an injector was first analyzed by using a two-phase flow analysis method [VOF (Volume of Fluid) model]. A time-series analysis was made of the flow though the injector and also of the air cavity that forms at the nozzle and influences fuel atomization. The calculated results made clear the process from initial spray formation to liquid film formation. Spray droplet formation was then analyzed with the synthesized spheroid particle (SSP) method. As the experimental approach, in order to measure the cavity factor that represents the liquid film thickness, nozzle exit flow velocities were measured by particle image velocimetry (PIV). Previously, these high velocities have been difficult to measure, but a newly developed PIV system using two CCD cameras to capture high-speed flow has made such measurement possible. Spray droplets sizes and surrounding air flow velocity fields were also measured by PIV.

These two approaches were applied to test nozzles, and the calculated results were compared with the experimental data. The relatively good agreement found between the two sets of results confirmed the effectiveness of these approaches.