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Ducted fuel injection (DFI) is an innovative method that curtails or prevents soot formation in direct-injection compression-ignition engines. DFI uses a simple duct, positioned outside each injector hole, facilitating the fuel/charge gas mixing before ignition. This reduces the equivalence ratio below two, in the autoignition zone, which in turn decreases soot formation. But this method also reduces fuel-conversion efficiency. This study investigates the effects of DFI on in-cylinder heat transfer. Experiments with conventional diesel combustion (CDC) and DFI were performed at four different dilution levels. Computational fluid dynamics (CFD) simulations were carried out at conditions matching those of the experiments,more » and the simulations were validated by the experimental data. The CFD simulations enabled to examine of in-cylinder heat release and temperature distributions. The heat transfer to the piston, head, and cylinder was investigated. The results show that DFI increased the heat transfer to the walls compared to CDC under the same conditions. This could help explain why DFI has been observed to reduce fuel-conversion efficiency by approximately 1% (absolute) relative to CDC under certain conditions. The efficiency loss typically decreases with dilution, such that DFI can improve fuel-conversion efficiencies relative to CDC at higher dilution levels.« less

Ducted fuel injection (DFI) is a technique to attenuate soot formation in compression ignition engines relative to conventional diesel combustion (CDC). The concept is to inject fuel through a small tube inside the combustion chamber to reduce equivalence ratios in the autoignition zone relative to CDC. DFI has been studied at loads as high as 8.5 bar gross indicated mean effective pressure (IMEP_g) and as low as 2.5 bar IMEP_g using a four-orifice fuel injector. Across previous studies, DFI has been shown to attenuate soot emissions, increase NO_x emissions (at constant charge dilution), and slightly decrease fuel conversion efficiencies formore » most tested points. This study expands on the previous work by testing 1.1 bar IMEPg (low-load/idle) conditions and 10 bar IMEPg (higher-load) conditions with the same four-orifice fuel injector, as well as examining potential causes of the degradations in NO_x emissions and fuel conversion efficiencies. DFI and CDC are directly compared at each operating point in the study. At the low-load condition, the intake charge dilution was swept to elucidate the soot and NO_x performance of DFI. The low-load range is important because it is the target of impending, more-stringent emissions regulations, and DFI is shown to be a potentially effective approach for helping to meet these regulations. The results also indicate that DFI likely has slightly decreased fuel conversion efficiencies relative to CDC. We find that the increase in NO_x emissions with DFI is likely due to longer charge gas residence times at higher temperatures, which arise from shorter combustion durations and advanced combustion phasing relative to CDC.« less

Ducted fuel injection (DFI) has been shown to attenuate engine-out soot emissions from diesel engines. The concept is to inject fuel through a small tube within the combustion chamber to enable lower equivalence ratios at the autoignition zone, relative to conventional diesel combustion. Previous experiments have demonstrated that DFI enables significant soot attenuation relative to conventional diesel combustion for a small set of operating conditions at relatively low engine loads. This is the first study to compare DFI to conventional diesel combustion over a wide range of operating conditions and at higher loads (up to 8.5 bar gross indicated meanmore » effective pressure) with a four-orifice fuel injector. This study compares DFI to conventional diesel combustion through sweeps of intakeoxygen mole fraction (XO₂), injection duration, intake pressure, start of combustion (SOC) timing, fuel-injection pressure, and intake temperature. DFI is shown to curtail engine-out soot emissions at all tested conditions. Under certain conditions, DFI can attenuate engine-out soot by over a factor of 100. In addition to producing significantly lower engine-out soot emissions, DFI enables the engine to be operated at low-NO_x conditions that are not feasible with conventional diesel combustion due to high soot emissions.« less

Ducted fuel injection (DFI) has been introduced as a strategy to enhance the fuel/charge gas mixing within the combustion chamber of a direct-injection mixing-controlled compression ignition engine. The concept involves injecting each fuel spray through a small tube within the combustion chamber to facilitate the creation of a leaner mixture in the autoignition zone, relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). While previous experiments demonstrated that DFI lowers both soot incandescence and soot mass in a constant-volume combustion vessel with a single-component normal-alkane fuel (n-dodecane), here we provide the firstmore » evidence that the technology provides similar benefits in an engine application using a commercial diesel fuel containing ~30 wt% aromatics. The present study investigates the effects on engine-out emissions and efficiency with a two-orifice injector tip for charge gas mixtures containing 16 and 21 mol% oxygen. The result is that DFI is confirmed to be effective at curtailing engine-out soot emissions. It also breaks the tradeoff between emissions of soot and nitrogen oxides (NOx) by simultaneously attenuating soot and NO_x with increasing dilution.« less