Investigation on fuel adhesion characteristics of wall-impingement spray under cross-flow conditions

The impingement of fuel spray on the piston surface significantly affects the mixture formation, combustion performance, and emissions of a direct-injection spark-ignition (DISI) engine. Therefore, the fuel adhesion characteristics of wall-impingement spray were investigated under cross-flow conditions for in-depth understanding the fuel adhesion behavior in this work. Mie scattering and refractive index matching (RIM) were used to observe the propagation of fuel spray and fuel adhesion, respectively. Subsequently, the area, mass, and thickness of fuel adhesion were evaluated under various cross-flow velocities. The results demonstrated that the cross-flow enhanced the diffusion of fuel spray and fuel adhesion, exhibiting an ellipse propagation. Additionally, the cross-flow also accelerated the volatilization of fuel adhesion, so that the adhesion area and mass decreased with time. Furthermore, the average fuel adhesion thickness obviously decreased under the cross-flow conditions. The fuel adhesion was divided into thick and thin fuel adhesion regions based on the distribution of fuel adhesion. Moreover, the formation and propagation mechanism of the fuel adhesion under cross-flow conditions were revealed. The experimental results can provide an insight into the operating conditions of air-flow inside the engine.