Numerical Analysis of the Fuel Mixing Process in a Multi-Fuel Injection System

The paper focuses on the mixing process of different fuels in a multi-fuel, low-pressure, common-rail injection system for a four\-stroke SI engine. The study is devoted to the prediction of the fuel mixture delivered by the injectors during a transient in which gasoline is being replaced by ethanol or a gasoline/ethanol blend. An integrated approach of different numerical tools is used to model the rail dynamic behavior under actual operating conditions.First, the 1D model of the injection system is constructed and the time-varying conditions at the accumulator inlet and at the injectors' boundaries are assessed. The second step of the study is centered on the CFD analysis of the mixing process within the rail. The effects of the different engine operations on the fuels mixing are investigated and the injected fuel distribution among the cylinders is calculated. An open source computational fluid dynamics code is used in the simulations. The modified VOF approach, used for modelling the fluid-fluid mixing process, is tailored in order to account for the turbulence effect.