Digital Shaping and Optimization of Fuel Injection Pattern for a Common Rail Automotive Diesel Engine through Numerical Simulation

Development trends in modern Common Rail Fuel Injection System (FIS) show dramatically increasing capabilities in terms of optimization of the fuel injection pattern through a constantly increasing number of injection events per engine cycle along with a modulation and shaping of the injection rate. In order to fully exploit the potential of the abovementioned fuel injection pattern optimization, numerical simulation can play a fundamental role by allowing the creation of a kind of a virtual injection rate generator for the assessment of the corresponding engine outputs in terms of combustion characteristics such as burn rate, emission formation and combustion noise (CN). This paper is focused on the analysis of the effects of digitalization of pilot events in the injection pattern on Brake Specific Fuel Consumption (BSFC), CN and emissions for a EURO 6 passenger car 4-cylinder diesel engine. The numerical evaluation was performed considering steady-state conditions for 3 key points representative of typical operating conditions in the low-medium load range. The optimization process was carried out through numerical simulation, by means of a suitable target function aiming to minimize BSFC and CN while not exceeding the target NOx emissions level. By means of a previously developed fuel injection system model, possible different injection patterns with high number of pilot injections were evaluated thus obtaining a kind of virtual injection rate generator, the outcomes of which were then used as input for a DIPulse combustion model in order to predict BSFC, combustion noise and emissions. Through numerical optimization of pilot injection pattern digitalization, potential for achieving significant reductions in BSFC and CN for low load engine points while not exceeding the target NOx emissions level, was demonstrated.