Spray Visualizaton of Air-Assisted Fuel Injection Nozzles for Direct Injection SI-Engines

A single cylinder engine was modified to study the potential of reducing fuel consumption and emissions in stratified, direct injection, spark ignition engines with the use of air-assisted nozzles. The spray angle of the nozzle was varied (60° and 90°), and two injection strategies were investigated: (I) the fuel was injected in the nozzle prior to transportation into the chamber via the air flow and (II) the fuel was injected directly into the air flow.

The results of the engine experiments were compared with the spray characteristic of each configuration. To facilitate the comparison, two-dimensional images of the sprays were recorded under atmospheric conditions. The fuel was visualized using Planar Laser-Induced Fluorescence (PLIF). The optical chamber was equipped with three optical accesses and a standard injection system from a production engine. The temporal and spatial developments of the spray were investigated for different types of nozzles and for the various injection strategies in both the optical chamber and the engine.

By varying the spray angle, the characteristics of the spray changed. Nozzles with smaller spray angles demonstrated more compact sprays, nozzles with greater angles demonstrated a hollow cone spray. The only experiments giving a homogeneous mixture were the engine experiments with the 60°-nozzle and injection into the intake stroke. Using the 90°-injector the fuel distribution prior to ignition was inhomogeneous and high cycle-to-cycle fluctuations were observed.