Study of the fluctuation in the cycle fuel injection quantity in a common-rail system for a heavy-duty vehicle diesel engine

A common-rail system can satisfy both diesel engine emissions legislation and fuel economy by flexibly regulating the injection pressure, the injection timing, the injection duration and the injection rate. Variations in the parameters of the common-rail system influence the injection characteristics and lead to fluctuation in the cycle fuel injection quantity. This fluctuation in the cycle fuel injection quantity is very critical for the coherence and stability of the common-rail system and the diesel that it injects. A new numerical model of a diesel engine’s common-rail system was developed in AMESim to investigate the cycle fuel injection quantity fluctuation. The predicted results of the rail pressure and the injection rate by the model are in excellent agreement with the experimental results obtained from a test bench. The influence law and the generation mechanism of the cycle fuel injection quantity fluctuation caused by variations in the different parameters are analysed in detail. Moreover, the quantitative percentages of fluctuation in the cycle fuel injection quantity are computed through analysis. The results show that the solenoid pre-tightening force, the orifice diameter of the outlet, the orifice diameter of the inlet and the needle lift are the four critical influential parameters of the common-rail system. Finally, a correlation analysis method was carried out on the cycle fuel injection quantity. The analysis results show that not only the first-order factors of the influential parameters but also the second-order factors which consider the interaction between the influential parameters have significant correlation with the cycle fuel injection quantity.