Effect of Partial Needle Lift on the Nozzle Flow in Diesel Fuel Injectors

Needle lift profile influence on the vapor phase penetration for a prototype diesel direct acting piezoelectric injector

“…As expected, an increase in injection pressure produces an increase in vapor penetration rates. These results agree with those previously obtained for the momentum flux and mass flow rates of this same injector by the authors in [8] [9] and the relation between mass flow rate, momentum flux and outlet velocity [25] [26].…”

“…This means that the piezo stack charge effect over spray development is noticeable from the start of injection, unlike the injection pressure effect. This behavior was noticeable already when the first hydraulic characteristic measurements were performed in [8] at the beginning of the study of this injector, and it also appeared in the liquid penetration curves shown in [10], measured later. The results presented, along with those obtained in these two previous studies, clearly confirm that this is a consistent behavior and that the needle lift plays a key role in both the transient and the steady stages of the injection process.…”

“…The lift profile in this case follows a ramp, that lifts the needle gradually, and not rapidly like in the square case, to the maximum lifts which yields, again, the same injection rate [10]. The injector's instant mass flow rates were previously measured in [8] for each condition in the test plan and are also represented in the following figures to better understand the behavior of the injector.…”

“…The study was performed using commercial Diesel fuel with a density of 812 kg/m 3 (at 70º) and kinematic viscosity of 1.9 10 -6 mm 2 /s (at 70º). The fuel was injected using with a 7-orifice nozzle (Outlet diameter D 0 = 156 µm, k-factor = 1.5 [8]) which permits full control of the needle lift position through the voltage profiles applied to the piezo stack [9]. The complete injection system is electronically controlled by the ECU and all the settings are introduced digitally.…”

“…Although there has been research works performed to analyze the injection event using conventional servo-hydraulic injectors, only a few are discussing the effect of the partial needle lift on the injection process [8][9] [10]. In order to develop a better understanding of the effect of partial needle lift on the atomization and evaporative performance of the injector, this research has carried out an experimental study to measure vapor phase penetration of the fuel spray produced by a direct acting injector, using a controlled 2-pass Schlieren setup.…”