Characterization of Internal Flow and Spray Behaviors of Hole-Type Nozzle under Tiny and Normal Injection Quantity Conditions for Diesel Engine 2016-01-0862

The tiny and normal injection quantity instances usually happen under the multi-injection strategy condition to restrain the uncontrollability of the ignition timing of the homogeneous charge compression ignition (HCCI) combustion concept. Meanwhile, instead of the traditional and fundamental single-hole diesel injector, the axisymmetric multi-hole injectors are usually applied to couple with the combustion chamber under most practical operating conditions. In the current paper, the internal flow and spray characteristics generated by single-hole and multi-hole (10 holes) nozzles under normal (2 mm³/hole) and tiny (0.3 mm³/hole) injection quantity conditions were investigated in conjunction with a series of experimental and computational methods. High-speed video observation was conducted at 10000 and 100000 fps under the condition of 120 MPa rail pressure, 1.5 MPa ambient pressure, room temperature, and nitrogen environment to visualize different spray properties. Moreover, the CFD calculation was also conducted under the same condition to reproduce the internal flow patterns inside different nozzles, which provided material for additional discussion and explanations for the mechanisms behind the spray behaviors. It revealed that the multi-hole nozzle had lower sac pressure and injection rate, longer injection duration, shorter spray tip penetration, and wider spray angle and spray cone angle compared to those of the single-hole nozzle. Meanwhile, the simulation study predicted that the internal flow patterns inside the multi-hole nozzle had more complicated vortex and turbulence structure and higher level of cavitation than the single-hole one. However, under different injection quantity conditions, the difference in the internal flow and spray behaviors between the single-hole and multi-hole nozzles presented distinctly different properties. It was concluded that the effect of the injection quantity plays different roles in the internal flow and near-field spray properties of the nozzles with distinct geometry and structure.