Multi-step approaches for comprehensive modeling of diesel engine fuel injection processes

The overall optimization of diesel fuel injection equipment and combustion process is mandatory to fulfill the future emission regulations. Among the involved phenomena, a preliminary role is played by the strong link between the combustion behavior and the adopted strategies to promote the mixing of reactants. The aim of the present work is to develop a comprehensive modeling approach, having the capability to take the deep connection between fuel injection phenomena into account. For this scope, different computational tools, characterized by different roles, have been used and coupled, accounting for the interdependencies of the relevant sub-processes. Three main multi-step modeling approaches are outlined and then used in the analysis of practical cases; these can be summarized as follows: 1) multi-step modeling (0D-3D CFD) for injection process and spray simulation with a unitary approach; 2) double step modeling (3D-0D) of fuel metering component operation; 3) comprehensive multi-step lumped modeling of injection system operation, spray formation and fuel vaporization. The mechanical-hydraulic modeling of the injection systems is based on the 0-1D code AMESim. To model the in-cylinder flows and the 3D transient nozzle flow, the commercial FIRE code is used, whereas the lumped modeling of evaporation processes in cylinder ambient is self FORTRAN implemented. Several cases have been considered and the contribution of the modeling approach is presented evaluated. Two different injection system types (inline pump and common rail systems) are considered in the applications. Investigations are devoted to evaluate the influence on injection process of fuel characteristics and composition, injection strategies, injector layout, geometrical features and needle operating conditions.