Emissions Benefits of Group Hole Nozzle Injectors under Conventional Diesel Combustion Conditions

This work explores the effectiveness of common rail fuel injectors equipped with Grouped Hole Nozzles (GHNs) in aiding the mixing process and reducing particulate matter (PM) emissions of Conventional Diesel Combustion (CDC) engines, while maintaining manageable Oxides of Nitrogen (NOx) levels. Parallel (pGHN), converging (cGHN) and diverging (dGHN) - hole GHNs were studied and the results were compared to a conventional, single hole nozzle (SHN) with the same flow area. The study was conducted on a single cylinder medium-duty engine to isolate the effects of the combustion from multi-cylinder effects and the conditions were chosen to be representative of a typical mid-load operating point for an on-road diesel engine. The effects of injection pressure and the Start of Injection (SOI) timing were explored and the tradeoffs between these boundary conditions are examined by using a response surface fitting technique, to identify an optimum operating condition. It is found that the GHNs offer a significant PM benefit along with a negligible NOx effect and that the cGHN and dGHN nozzles give the best PM performance at two different conditions. Furthermore, it was observed that GHN effects are dominated by injection pressure effects as the injection pressure was increased, with the differences between GHNs and the SHN becoming negligible above 1500 bar. A strong dependence on the injection timing was also seen, with the differences between GHNs and SHN being strongest when the injection occurs at, and just after, top dead center, suggesting that an optimum between power, emissions and injection pressure can be attained through GHN use in the medium duty sector.