Air-assisted fuel sprays have been investigated experimentally with schlieren technique and direct photograph. Schlieren photograph showed clear boundary of fuel vapor-air mixing region under simulated 2-stroke engine operating condition in atmospheric spray chamber. Direct photograph which provided distribution of liquid fuel was obtained simultaneously with schlieren photograph. These two photographs were compared each other to study qualitatively the difference between liquid and vapor fuel distributions. A number of parameters have been selected for this experiments, such as injected fuel and air masses, swirl velocity, simulated scavenging flow in 2-stroke engine and deflector angle in front of nozzle outlet.
The test results have showed that fuel initially emerges from the injector as hollow-cone jet. This two-phase jet collapses downstream as entrainment of air produces a low-pressure region beneath the poppet. Increase of injected fuel/air ratio resulted in decrease of axial penetration and increase of radial spread. Most of liquid fuel was shown crowded near spray axis, however, fuel vapor was shown at broader region in the final stage of injection. Large deflection of fuel spray was induced by swirl at all test conditions.
