Numerical study of purging of a gasoline direct injection nozzle at the end of injection

In gasoline direct injection engines, fuel injector nozzle is one of the vital components that determine the efficiency of fuel atomization which controls combustion and emission. There is an increased focus on developing better nozzles by studying the internal flow behavior especially during the needle transient phase and at the end of injection phase. Multiphase flow characteristics involving cavitation and hydraulic flip are observed inside the nozzle during its operation. At the end of injection, fuel inside the nozzle sac and nozzle holes is purged with the gas from the engine cylinder. The efficiency of this purging process is critical to prevent the carbon deposit formation on the wall of nozzle holes and on the surface of the nozzle tip. In this article, a numerical method is presented to predict the internal nozzle flow during the needle movement and during the end of injection to predict the purging capacity of a gasoline direct injection nozzle. Needle motion is accomplished using a moving mesh method via a user-defined function. The numerical model is compared with the X-ray measurements from the literature. Based on the validated model, the study is extended to analyze various parameters like injection pressure, nozzle hole location, number of nozzle holes and the inlet rounding of the nozzle hole which affects the effectiveness of nozzle purging. Fuel wetting at the nozzle tip after the end of injection is also numerically modeled to evaluate the thickness profile of the thin liquid film.