Droplet Behaviors of DI Gasoline Wall Impinging Spray by Spray Slicer 2020-01-1152
Owing to the small size of engines and high injection pressures, it is difficult to avoid the fuel spray impingement on the combustion cylinder wall and piston head in Direct Injection Spark Ignition (DISI) engine, which is a possible source of hydrocarbons and soot emission. As a result, the droplets size and distribution are significantly important to evaluate the atomization and predict the impingement behaviors, such as stick, spread or splash. However, the microscopic behaviors of droplets are seldom reported due to the high density of small droplets, especially under high pressure conditions. In order to solve this problem, a “spray slicer” was designed to cut the spray before impingement as a sheet one to observe the droplets clearly. The experiment was performed in a constant volume chamber under non-evaporation condition, and a mini-sac injector with single hole was used. The filtering device should be as less intrusive as possible, so to detect a momentum flux distribution corresponding to the un-disturbed free spray. To fulfill this basic requirement, different slice thickness (St) were tested by comparing the droplets behaviors through Particle Image Analysis (PIA) method. The droplet size and velocity distributions were presented and discussed. Results show that the “spray slicer” works better to cut the spray with smaller St. However, the velocity of the droplet at the tip of the spray decreases sharply with a decrease in St. When St = 0.4 mm, the dense region of the spray tip shows clear structure with less overlap droplets and the velocity is almost the same as that of St = 0.8 mm. Furthermore, the droplets diameter-velocity, velocity and diameter-minimum thickness distributions at different locations were analyzed.