Investigation of Ducted Fuel Injection Implementation in a Retrofitted Light-Duty Diesel Engine through Numerical Simulation

Ducted Fuel Injection (DFI) is a concept of growing interest to abate soot emissions in diesel combustion based on a small duct within the combustion chamber in front of the injector nozzle. Despite the impressive potential of the DFI proven in literature, its application for series production and the complexity for the adaptation of existing Compression-Ignition (CI) engines need to be extensively investigated. In this context, the aim of this study is to numerically assess the potential of DFI implementation in a CI engine for light-duty applications, highlighting the factors which can limit or facilitate its integration in existing combustion chambers.

The numerical model for combustion simulation was based on a One-Dimensional/Three-Dimensional Computational Fluid Dynamics (1D/3D-CFD) coupled approach relying on a calibrated spray model, extensively validated against experimental data. Once the coupling procedure had been assessed by comparing the numerical results with experimental data of in-cylinder pressure and heat release rate for both low- and high-load operating conditions, the effect of the duct was investigated by introducing it in the computational domain. It was observed that DFI did not yield any significant advantage to engine-out soot emissions and fuel consumption with the existing combustion system. Although soot formation was generally reduced, the soot oxidation process was partially inhibited by the adopted duct keeping the fixed engine calibration, suggesting the need for a complete optimization of the combustion system design. On the other hand, a preliminary variation of engine calibration highlighted several beneficial trends for DFI, whose operation was improved by a simplified injection strategy.

The present numerical results indicate that DFI retrofit solutions without specific optimization of the combustion system design do not guarantee soot reduction. Nevertheless, there is still much room for improvement in terms of DFI-targeted combustion chamber design and engine calibration to achieve the full success of this technology for soot-free CI engines.