The effect of split injection on fuel adhesion characteristics under static flow and cross-flow field conditions

The flat-wall wetting phenomenon is inevitable because of the smaller cylinder volume and higher injection pressure inside direct-injection spark ignition (DISI) engines. The fuel adhesion phenomenon after wall impingement negatively affects the fuel spray mixture formation, the fuel consumption, and the pollutant emissions. In this study, the effects of different fuel injection strategies on the wall-impingement behavior were compared under static flow and cross-flow field conditions. The refractive index matching (RIM) method and high-speed video (HSV) camera were adopted to measure the propagation of fuel adhesion and the spray structure of the vertical plane, respectively. Meanwhile, a dimensionless parameter named “deformation coefficient I_d,” which is defined as the fuel adhesion length divided by the width, is proposed to evaluate the degree of distortion of the fuel adhesion. Therefore, when I_d approaches 1, the fuel adhesion shape approaches a circle. The results show that the cross-flow promotes the diffusion of the fuel spray, which leads to an increase in the fuel adhesion area. The fuel adhesion shape is similar to that of a slender strip under cross-flow field conditions, but almost maintains a circle under static flow field conditions. The cross-flow decreased the average fuel adhesion thickness. Meanwhile, the cross-flow also promotes the evaporation of the adhered fuel on a flat-wall, which leads to a reduction in the fuel adhesion area and mass with time. Additionally, it was found that triple injection can decrease the fuel adhesion thickness, area, and mass ratio under cross-flow field conditions. To achieve carbon neutrality, optimizing fuel injection strategies to reduce emissions is one of the primary purposes of this study.