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
slicer thickness (Tslicer) 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 Tslicer.
However, the velocity of the droplet at the tip of the spray decreases sharply
with a decrease in Tslicer. When Tslicer = 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 Tslicer = 0.8 mm.
Furthermore, the droplets diameter-velocity, velocity and diameter-minimum
distance distributions at different locations were analyzed.