Influence of dwell time on the hydraulic behaviour utilizing multiple injection strategies and a piezoelectric diesel injector

Abstract

The electric dwell time is defined as the duration between two electric pulse signals. It is a crucial parameter when multiple injection strategies are employed. The influence of electric dwell time on the hydraulic behaviour utilizing pilot injection strategy, split injection strategy, post injection strategy and a commercial piezoelectric diesel injector has been analysed experimentally. To do so, a sweep of electric dwell time from 1.15 ms up to 3 ms in all multiple injection strategies using rail pressures of 80, 100 and 120 MPa, and a back pressure of 5 MPa was performed. A fuel mass of 110 mg was injected in all cases analysed employing operating conditions defined from the characteristics curves of injected mass. The hydraulic behaviour was characterized through to measure the first and second hydraulic delay at opening and closing injector, the pressure oscillations generated during the first injection event, and injected fuel mass during second injection event in an injection discharge curve indicator, which is based on the Bosch tube method. In summary, the paper concludes that the hydraulic dwell time depends on the injected mass during the first injection event, and the dynamic response of injector. Moreover, a short electric dwell time causes an increase of injected fuel mass during second injection event, which can be attributed to combine two effects provoked by overlapping the first and second mass flow rate signals, namely, a reduction in the hydraulic delay at opening injector, and an increase in the hydraulic delay at closing injector. Finally, the present research provides information which can be employed to optimization the modulation of injection rate in a diesel engine.