Ducted fuel injection (DFI) was tested for the first time in a heavy-duty diesel metal engine. It was implemented on a Caterpillar 2.5-liter single-cylinder heavy-duty diesel engine fitted with a common rail fuel system and a Tier 4 final production piston. Engine tests consisted of single-injection timing sweeps at A100 and C100, where rail pressure and exhaust gas recirculation (EGR) were also varied. A 6-hole fuel injector tip with 205 am orifices was used with a 130° spray angle and rail pressures up to 250 MPa.
The ducts were 14 mm long, had a 2.5 mm inner diameter, and were placed 3.8 mm away from the orifice exits. The ducts were attached to a base, which in turn was attached to the cylinder head with bolts. Furthermore, alignment of the ducts and their corresponding fuel jets was accomplished.
The objectives of this study were to compare performance and emissions trade-off curves for DFI and conventional diesel combustion (CDC) at high load and evaluate whether DFI could be successfully retrofitted into a production-like combustion system.
Results suggest that a combustion system may need to be designed for DFI - retrofitting without base engine hardware modifications may not work. At these high load operating conditions DFI generally yielded increased PM emissions. Unburned hydrocarbons and carbon monoxide also generally increased with DFI. Fuel consumption with DFI matched CDC at some injection timing locations, but generally increased. DFI generally performed better at retarded injection timing and higher rail pressures, possibly suggesting that DFI favors lower combustion temperatures.