CHARACTERIZATION OF CONICAL SPRAY FLOW FOR DIESEL-ENGINE BY MEANS OF LASER-DOPPLER METHODS (PDA MEASUREMENT OF DROPLET SIZE DISTRIBUTION)

To study the flow characteristics and particle diameters in a wide-ang le conical spray proposed for premixed combustion diesel engines, an u nsteady conical spray in air has been analyzed using a phase Doppler a nemometer (PDA). In these experiments, the injection frequency is 20.8 Hz and the fuel injection quantity is 10.3 mg per cycle. Axial and ra dial bulk particle velocities and mean particle diameter distributions are obtained. As a result, it is found that the mean velocity distrib ution profile resembles the Goertler distribution, and the Sauter mean droplet diameter in the conical spray is as small as 30 mu m. The rel ationship between particle diameter and velocity over the entire spray is negative and unusual compared with steady pressure spray flows, bu t is found to be normal if the spray is divided into several parts. We also find that small-diameter particles (20 mu m) which are injected at a high speed (60 m/s)in the earliest stage lose velocity rapidly, m erge into bigger particles, and are overtaken by bigger but slower par ticles which are emitted during a later stage. Large-diameter (50 mu m ) particles gather at the tip of the spray since they travel further f rom the nozzle exit.