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.
