Characteristics of Nozzle Internal Flow and Near-Field Spray of Multi-Hole Injectors for Diesel Engines 2015-01-1920
The combustion process, emission formation and the resulting engine performance in a diesel engine are well known to be governed mainly by spray behaviors and the consequent mixture formation quality. One of the most important factors that affect the spray development is the nozzle configuration. Originally, single-hole diesel injector is usually applied in fundamental research to provide insights into the spray characteristics. However, the spray emerging from a realistic multi-hole injector approaches the practical engine operation situation better. Meanwhile, previous research has shown that the reduced nozzle hole diameter is effective for preparing more uniform mixture. In the current paper, a study about the effects of nozzle configuration and hole diameter on the internal flow and spray properties was conducted in conjunction with a series of experimental and computational methods. Two multi-hole nozzles (10 holes) with different hole diameter (D=0.10 mm and 0.07mm) and another two referential single-hole nozzles were applied in Mie-scattering experiments. High-speed images of sprays from each nozzle were freeze-captured at 10000 and 100000 frames per second under the condition of 2.0 mm3/hole injection quantity, 120 MPa injection pressure, 1.5 MPa ambient pressure, room temperature, and air environment. The experimental results revealed that under D=0.10 mm condition, the multi-hole nozzle had lower 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. However, under D=0.07 mm condition, the differences of injection rate, injection duration, spray tip penetration, and spray angle between two nozzles were quite small, although multi-hole nozzle still had a little wider spray cone angle. Moreover, aiming to correlate the observed spray characteristics to the internal flow phenomenon, CFD simulation was also conducted under the same condition, which provided additional explanations for the spray behaviors.