Characteristics of wall-jet vortex development during fuel spray impinging on flat-wall under cross-flow conditions

Spray wall-impingement is unavoidable in direct-injection spark-ignition engines, and it affects the formation and combustion process of the mixture, resulting in significant emissions and fuel economy problems. In addition, the airflow in the cylinder inevitably affects spray propagation. Therefore, the influence of cross-flow on the wall-impingement spray behavior was investigated in this work. Laser sheet technology was applied to obtain the macroscopic structure of the wall-impinging spray, and the wall-jet vortex region was observed in the wall-impinging spray tip. Under different ambient pressures (0.1 and 0.4 MPa), the structure of the wall-jet vortex was determined at three different cross-flow velocities (0, 2, and 5 m/s) and three wall-impingement distances (25, 50, and 75 mm). Furthermore, an indicator I_c of the “contribution index” was proposed to evaluate the degree of influence of various influencing factors on the wall-jet vortex. The results reveal that the ambient pressure has a significant effect on the vortex core height. The vortex core height is reduced by approximately 30% as the ambient pressure increases from 0.1 to 0.4 MPa. Meanwhile, cross-flow also significantly increases the vortex core height. It is also noted that the development of the vortex core distance is more sensitive to cross-flow. A cross-flow velocity of 5 m/s increases the vortex core distance by approximately 30%. In addition, the timing of the spray wall-impingement is delayed with an increase in the wall-impingement distance. These results pertaining to the wall-jet vortex characteristics can provide the necessary guidance and suggestions for better understanding the wall-impingement spray behavior.