Ducted fuel injection investigation applied in light-duty compression ignition engines

Ducted fuel injection (DFI) is a promising technology that can modify the combustion process in compression ignition engines to mitigate soot formation. By guiding the spray through ducts, air entrainment is enhanced, promoting a more pronounced premixed combustion phase, reducing the diffusion flame, and consequently suppressing soot generation. While previous studies using constant-volume chambers and optical research engines have demonstrated the potential of DFI and the influence of injector geometry on emissions, few have implemented this approach directly in engines due to the substantial modifications required to the cylinder head. This study proposes and evaluates an alternative DFI configuration suitable for light-duty compression ignition engines, implemented without significant modifications to the engine head. Experiments were conducted in a single-cylinder research engine using a sleeve fitted to the injector, aligning the ducts with the nozzle holes. The limited space introduces constraints such as a trade-off between duct length and stand-off distance, and a duct length shorter than the theoretical liquid penetration length. Results show that the configuration with a 3.5 mm stand-off distance achieved up to a 70% reduction in soot emissions compared to the free-spray baseline, while shorter stand-off distances (2.5 and 3.0 mm) were less effective. Although DFI delays ignition, it enhances air entrainment and premixed combustion, ultimately accelerating the combustion process.