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

An experimental study has been performed to evaluate the impact of different needle partial lifts on the nozzle orifices flow. A prototype injector with a multi-orifice nozzle was used. This injector allows controlling the needle lift at different percentages of maximum lift. Different measures of mass flow rate and spray momentum flow at several rail pressures (up to 200 MPa) were made in order to observe the effect of different needle lift percentages on the amount of fuel injected and momentum of the jet.

The influence of partial needle lifts on nozzle orifices flow was estimated by using non-dimensional parameters of discharge coefficient (C_d), velocity coefficient (C_v) and area coefficient (C_a). The results show an interesting reduction in nozzle discharge coefficient at partial lift. This reduction of C_d value at partial needle lift is not only due to the drop in the velocity coefficient but also to a reduction of the effective orifice area. This decrease in the area coefficient (C_a) at partial lift compare with the value at full needle lift evidences that the flow through the nozzle orifices is not controlled only by the pressure at the inlet of the orifices but also by the velocity profiles at the inlet of the orifice, which is frequently neglected in the numerical calculations.