Effect of injector type on fuel-air mixture formation of high-speed diesel sprays

Abstract

This study was performed to analyse the characteristics of fuel sprays issued from a piezo-driven injector and to compare both experimental results and numerical predictions with those from a solenoid-driven injector. In order to study the effect of the injector type, two injectors with the same specifications - except for their drive type - were used in the experiments. In this work, the profiles of injection rates, processes of spray development, mean droplet size distributions, and mean velocities were obtained using an injection rate meter, a spray visualization system, and a phase Doppler particle analyser (PDPA) system. In order to calculate the atomization process of the injected spray, the Kelvin-Helmholtz instability/droplet deformation and break-up ((KH-DDB) model was used, and the prediction accuracies were verified by comparing them with experimental results. For the numerical approach using the KIVA code, the nozzle flow and droplet break-up models were modified to consider the conditions of a common-rail injection system. The input parameters for the KIVA calculations were determined based on the nozzle flow model considering the effect of cavitation. In addition, the effects of injector type on the evaporation characteristics were calculated using the modified Spalding evaporation model. This study reveals that the injection delay of the piezo-driven injector is shorter than that of the solenoid-driven injector by 0.06 ms, and that the atomization and evaporation performances of the fuel spray can be enhanced by using the piezo injector instead of the solenoid injector.