Research on effects of key influencing factors upon fuel injection characteristics of the combination electronic unit pump for diesel engines

A numerical model of the combination electronic unit pump (CEUP) fuel injection system was developed in AMESim environment. The effects of five key influencing factors, including cam profile velocity, plunger diameter, length of high pressure fuel pipe, inner diameter of high pressure fuel pipe and nozzle flow rate on injection characteristic parameters, were analyzed by using the developed numerical model. On the basis, a correlation analysis between the influencing factors and injection characteristics was performed by using the design of experiments (DoE) method, and the influences of these factors were quantized accordingly. Relevant results show that both the single influencing factor and the interaction among these factors correlates with the injection characteristics, and the correlation represents a complex law with the cam rotational speed. The effect of plunger diameter on the injection pressure, cycle fuel injection quantity and injection duration is the most obvious, especially at a cam rotational speed of 500 r/min and the correlation coefficient is up to 0.82. The length of high-pressure pipe (HP pipe) has the most obvious influence on the coefficient of fuel feeding at cam rotational speed of 500 r/min and 800 r/min, and the correlation coefficient is negative. Overall, the independent influence of the factors is more significant than the combined influence of various factors. The CEUP fuel injection system is a complicated multi-input multi-output (MIMO) nonlinear system in fact.