Spray analysis of an innovative direct command solenoid injector for common rail light duty Diesel engines

An innovative direct command injector for common rail light duty direct injection Diesel engines able to control small fuel flow rates (0.1 mg/str) in the range of injection pressures from 20 to 70 MPa has been tested. The injector designed by Magneti Marelli, a 5 hole, 150° spray angle, 0.12 mm nozzle diameter, is a gasoline-derived designed using a new concept to control the amount of injected fuel and the rate shape. In fact, the injector needle lift is directly controlled by the solenoid current instead of being activated by the inner fuel hydraulic circuit. This allows to obtain a precise control of the amount of delivered fuel that is inversely related to the injection pressure. This paper aims at investigating the behaviour spray evolution from the new injector compared to that obtained by a commercial injection apparatus. The objective is to give an insight on the capability of the innovative injector to set multiple injection strategies with short dwell time. The commercial injector (Bosch), able to operate at multiple injection strategies, has been a 5 hole, 0.13 mm nozzle diameter, 150° spray angle, micro-sac nozzle having a flow rate of 270 cm3/30 sec@10 MPa. To characterize the behaviour of the injection systems, measurements of the instantaneous flow rate for different strategies have been carried out by the AVL fuel gauge meter. The investigation has been also conducted by using the imaging technique in order to explore the spray morphology at different time after the start of injection. The spray evolution, in terms of stability and spatial fuel distribution, has been investigated under non evaporative conditions, in a quiescent high-pressure optically-accessible vessel. Images of the spray evolution have been processed to estimate the liquid tip penetration. A comparison of the spray behaviour, under evaporative conditions, has been also performed testing the commercial injector in a single-cylinder optically-accessible engine. Tests, achieved on the innovative injector, have shown a good stability for small amount of delivered fuel with a uniform evolution of each jet. The investigation, also focused on the potential task to make consecutive injections, has confirmed the capability to control double and triple injections with short dwell time joined to the stability of the mass flow rate injected during the pilot injection. Moreover, the tip penetration has the same behavior for the main, in the double injection as well in the split main of the triple one. Further, results show that the Bosch injector delivers, at the same time after the start of injection, an equivalent amount of fuel in a shorter time compared to the Magneti Marelli one.