Evaluation of Pump Design Parameters in Diesel Fuel Injection Systems

A computer model solving the 1-D flow in a typical fuel injection system for direct-injection diesel engines is presented. A Bosch distributor - type VE pump connected to four Stanadyne pencil - type nozzles has been used to validate the computer model over a wide range of operating conditions. Validation of the developed computer code has been performed for eight representative test cases. The predicted values which were compared with the experimental ones include the pumping chamber pressure, the line pressure, the needle lift and the injection rate. Results using as input the measured pumping chamber pressure are also presented in order to identify the error in the injection rate signal attributed to the difference between the simulated and the experimental pumping chamber pressure. In addition, the total fuel injection quantity for pump speeds between 500 and 2000 rpm and lever positions between 20% to 100% was calculated and compared with measurements. The nozzle exit characteristics and mean effective injection pressure were quantified in terms of the mean line pressure and its variation with pump speed and lever position.

Following satisfactory validation of the code, parametric studies were performed in order to quantify the effect of pump design characteristics such as the cam lift and lever position on the start of injection, injection duration and total fuel injection quantity. In addition, the start of injection was defined as a function on the nozzle opening pressure and an equivalent pumping chamber opening pressure was derived.