Hydraulic response of different diesel injector typologies under multiple-injection strategies

Abstract

The response time of diesel injectors depends mainly on their internal hydraulic configuration. The present research is focussed on studying the response time of two solenoid diesel injectors (CRI2.1 and CRI2-18), and a piezoelectric diesel injector CRI3-18 by analysing the injection fusion threshold (IFT), the behaviour of nozzle opening delay (NOD) and nozzle closing delay (NCD) with energizing time, and the relationship between electric dwell time (DT) and hydraulic dwell time (DT_h) in split injection strategies. To do so, firstly, the characteristic curves of all diesel injectors studied were obtained. Secondly, in order to ensure an injected mass of 110 mg, the energizing times of first and second injection events for all multiple-injection strategies analysed were defined, using the characteristic curves. Thirdly, the mass flow rate and electric pulse signals of all cases studied were measured in an injection discharge curve indicator, using the levels of rail pressure (p_rail) of 80, 100, and 120 MPa, and a backpressure (p_b) of 5 MPa. Fourthly, the DT and DT_h values of all cases were determined from the electric pulse and mass flow rate signals. The DT is defined as the time interval between the end of first electric pulse signal and start of second electric pulse signal, whereas DT_h is defined as the time interval between the end of the first mass flow rate signal and start of the second mass flow rate signal. Among the main results obtained, it can be highlighted that the DT_h values of solenoid diesel injector CRI2.1 are higher than those of solenoid diesel injector CRI2-18 and piezoelectric diesel injector for all split injection strategies, and p_rail levels studied. Moreover, the DT_h values of piezoelectric diesel injector CRI3-18 are higher than those of solenoid diesel injector CRI2-18 for also all split injection strategies and p_rail levels studied.