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Current market drivers for automotive and light commercial engines and powertrain systems are mainly the new CO2 emission regulations all over the world and the pollutant emission reduction in the emerging markets, at minimal system cost. For both reasons, the adoption of a regulated electric low pressure fuel pump is very advantageous for electronically controlled diesel systems, customized for the emerging markets. Usually, the fuel delivery from the feed pump is performed at the maximum flow rate and a pressure regulator discharges the exceeding fuel amount either from the rail or upstream the high pressure pump. Therefore, at part load, the electric feed pump flow is higher than the request for engine power generation. For the purpose of this paper, the low pressure fuel pump is controlled for fuel delivery according to the engine request (reduced fuel consumption), thus avoiding the use of a pressure regulator valve (reduced cost).

Considering the world-wide market for GDI engines, the introduction of tighter polluting emission legislation, additional costs, vehicle fuel economy and pollutants reduction become substantial drivers. Focusing on particulate reduction, direct injection gasoline engines require advanced combustion strategies. The main levers used are injection splitting in order to reduce wall impingement (due to lower penetration) and higher rail pressure level to reduce droplet size. To reach this target it is necessary to improve precision in term of injected quantity in the small quantity region with high fuel rail pressure and during the actuation of multiple injections. As a consequence of the requirements of high quantities at full load, known GDI solenoid injectors show an unacceptable spread in terms of small injected quantity when the energizing time is small such that the injector works in the ballistic zone. Following these premises an electronic approach is needed.

The trend of CO2 emission limits and the fuel saving due to the oil price increase are important drivers for engines development. The involved technologies have the aim to improve the global engine efficiency, improving combustion and minimizing energy losses. The engine auxiliary devices electrification (i.e. cooling pump or lubricating pump) is a way to reduce not useful energy consumption, because it becomes possible to control them depending on engine operating point. This kind of management can be applied to the electric low pressure fuel pump. Usually the fuel delivery is performed at the maximum flow rate and a pressure regulator discharges the exceeding fuel amount inside the rail (i.e. gasoline engine) or upstream of the high pressure pump (i.e. common rail diesel engine). At part load, especially in diesel application, the electric fuel pump flow is higher than needed for engine power generation.

The paper investigates the variation of the mass of the fuel injected with respect to nominal conditions in Common Rail injection systems for Diesel automotive applications. Two possible operating conditions have been considered: the consecutive injection of two injectors and the multiple shots of the same injector in the same engine cycle. An integrated experimental and numerical methodology has been used. Several experimental information were available in terms of instantaneous rail and pipe pressure and mass flow rate at different conditions. The 1D numerical model of the whole injection system was useful in addressing the questions remained unresolved in the post-experiments analysis. The experimental results show that injector performances are more related to pressure oscillations in injector connecting pipe rather than inside the common rail.