Numerical Investigation of Critical Issues in Multiple-Injection Strategy Operated by a New C.R. Fast-Actuation Solenoid Injector 2005-01-1236

The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the consecutive injection of two injectors and the multiple shots of the same injector in the same engine cycle. An integrated experimental and numerical methodology has been used. Several experimental information were available in terms of instantaneous rail and pipe pressure and mass flow rate at different conditions. The 1D numerical model of the whole injection system was useful in addressing the questions remained unresolved in the post-experiments analysis. The experimental results show that injector performances are more related to pressure oscillations in injector connecting pipe rather than inside the common rail. The fuel mass is slightly depending on the mutual influence between two consecutive injectors while it is strongly affected by the dwell time (i.e., DTW) between consecutive shots of the same injector in the same engine cycle. The dwell time variation determines different pressure oscillation amplitudes in the injector connecting pipe at the electrical (nominal) start of the injection of the second pulse. As a consequence, different hydraulic (i.e., actual) start and duration of the injection of the second pulse occurs depending on dwell time. A parametric analysis showed that the injected fuel mass variation with dwell time can be reduced by using shorter and larger injector connecting pipes.