Innovative Lift Direct Command to Inner Hydraulic Circuit Injector Comparison for Diesel Engines

In this paper a comparative investigation between two different injectors for Common Rail diesel apparatus has been carried out in terms of transient response and spray pattern for different injection strategies. Performances of an innovative Magneti Marelli (MM) gasoline derived injector have been evaluated against the Bosch generation injectors for multiple strategies. Both injectors have operated on an automotive apparatus controlled by a Programmable Electronic Control Unit to set injection strategies in terms of pulses number, duration and dwell time. The working mode of the two injectors is completely different: the Bosch injector is activated by the inner fuel hydraulic circuit while the Magneti Marelli one operates a direct control of the needle lift through the solenoid currents. The Bosch nozzle characteristics are 5 holes, 150° spray angle, and 0,13 mm diameter. The MM injector main characteristics are low hydraulic losses, simple component structure and ready use of the fuel at the nozzle opening being able to control small fuel flow rates (0.1 mg/str) in the injection pressures range 20–70 MPa. The geometry of the nozzle is quite similar to the Bosch one being a 5 hole, 150° spray angle, 0.12 mm diameter. Single, pilot+main and pilot+split main strategies have been explored for the two injectors at 50 and 60 MPa injection pressures investigating the spray behavior for two amounts of injected fuel (5.0 and 6.5 mg/str). The systems have been characterized in terms of injected fuel rate as well spatial and temporal behavior of the emerging jets from the nozzle. Images of the spray have been collected by a synchronized CCD camera at different time from the start of injection. The jets have evolved in an optically accessible high pressure vessel at ambient temperature as well in an optically accessible single-cylinder 2-stroke Diesel engine extracting the fuel spray parameters from the collected images applying a digital processing techniques. Due to the diverse mechanism of the injector actuation, a different temporal and spatial fuel distribution has been registered for the two apparatuses. These could strongly influence the air/fuel mixture formation and combustion process with effect on the emissions. Preliminary engine tests performed on a light duty direct injection diesel engine, equipped with the MM injector, have highlighted the potential of the MM injector to handle acceptable engine performances.