Numerical study on the effects of fuel viscosity and density on the injection rate performance of a solenoid diesel injector based on AMESim

Abstract

A one-dimensional model of a solenoid diesel injector was developed under AMESim. The accuracy of the model was validated with the injection rate data from experiment. The objective of the research is to investigate the individual effects of fuel viscosity and density with fuel temperature on the injection rate numerically, because these two properties cannot be altered individually in reality. The kinematic viscosity of the fuel and the density were varied from 2.4 to 22.5 mm2/s, and 805 to 845 kg/m3, respectively, to cover a cold start environment. These two fuel properties contributed to the changes of two main forces inside the injector – the hydraulic force caused by the pressure difference across the needle, and the viscous friction force at the leakage passage. The influence of fuel viscosity on the injection rate was greater than the fuel density. Firstly, it was because the change of the fuel viscosity showed a greater span than the density under the fuel temperature range of interest. Secondly, the fuel viscosity influenced both the hydraulic and the viscous friction forces. The net hydraulic force decreased as the fuel viscosity increased due to lowered discharge coefficient of the flow across the orifices. The fuel viscosity further contributed in hindering the needle dynamics in the form of viscous friction force. Whereas, the fuel density mainly affected the change of the hydraulic force. The viscous friction force contributed as much as about 12% of the total driving force of the needle when the fuel viscosity increased.