Effect of cross-flow on spray structure, droplet diameter and velocity of impinging spray

The air flow and wall impingement in a direct-injection spark-ignition (DISI) gasoline engine affect the fuel-air mixture formation and the quality of fuel combustion. In this work, a comprehensive experimental investigation on the effect of cross-flow on the spray structure, droplet diameter and velocity distributions was carried out. The transient impinging spray behavior at different cross-flow velocities was recorded using high-speed photography with a continuous wave laser sheet. It was seen that a higher cross-flow velocity significantly increases the spray area, i.e., the cross-flow favors spray dispersion. Moreover, the spray outline distortion caused by cross-flow in the leeward side is larger than that in the windward side. By employing the particle image analysis (PIA) optical diagnostic method, the Sauter mean diameter (SMD) and the droplet velocity components were investigated. The results show that a higher cross-flow velocity causes an increased proportion of large droplets in the windward side of spray, and the enhanced droplet breakup, resulting in a larger SMD in the windward side of spray and smaller SMD in the leeward side of spray. In the leeward side of spray, the droplet horizontal velocity gradually increases along the cross-flow direction, and after it reaches approximately the cross-flow velocity, the droplet horizontal velocity shows a large fluctuation in the downstream region. Moreover, the droplet vertical velocity decreases sharply from the center line of the main spray body to the spray periphery. By comparing the velocities of droplets, we found that compared with larger droplets, the smaller droplets are more easily affected by a cross-flow owing to the effect of drag acceleration.