Medium Pressure Injection System for Small Diesel Engine Application: Numerical Simulation and Experimental Results

Diesel engine technology is continuously focused on higher performances and lower emission levels. Reduced costs and lower fuel consumption are key factors in engine development too, in particular for small diesel engine, both for on-road and non-road application. In order to fulfill emission legislation requirements, improve engine performance and reduce fuel consumption, nowadays the common rail injection system with electronic actuation is widely used in diesel engines. Nevertheless, conventional common rail system cost is quite high, mainly due to the complex indirect actuation of the injector, and the injector backflow leads to inefficiencies in the injection system. In this work an analysis of a medium pressure injection system for small diesel engines is presented, focusing on the achievable engine performances and emissions. The new injection system makes use of an innovative solenoid directly actuated injector (DDI) with a lower maximum rail pressure in respect with conventional common rail systems. A feasibility analysis of such a system for a light commercial vehicle (LCV) application is reported. Experimental tests on the new DDI injector have been carried out and its performances are evaluated and compared with a conventional system in terms of both hydraulic and spray behavior. In order to define the proper characteristics of the injection system, numerical analyses of the components have been performed, also considering in-cylinder CFD simulations of mixture formation and combustion. Then the considered injection system was tested on engine test bench. The results of experimental tests confirm the effectiveness of the new injection system in terms of performance, emission and above all engine fuel consumption.