Group-Hole Nozzle Effects on Mixture Formation and In-cylinder Combustion Processes in Direct-Injection Diesel Engines 2007-01-4050

The group-hole (GH) nozzle concept that uses two closely spaced micro-orifices to substitute the conventional single orifice has the potential to facilitate better fuel atomization and evaporation, consequently attenuate the soot emission formed in direct-injection (D.I.) diesel engines. Studies of quantitative mixture properties of the transient fuel spray injected by the group-hole nozzles were conducted in a constant volume chamber via the laser absorption-scattering (LAS) technique, in comparison with conventional single-hole nozzles. Specific areas investigated involved: the non-evaporating and the evaporating ambient conditions, the free spray and the spray impinging on a flat wall conditions. The particular emphasis was on the effect of one of key parameters, the interval between orifices, of the group-hole (SH) nozzle structure. Subsequently, following an optimization analysis, in-cylinder ignition and combustion processes were investigated by direct flame visualization in a single-cylinder optical research engine using the group-hole nozzle and the standard multi-hole nozzle, together with the heat-release analysis.

Results show that the group-hole nozzle can produce a smaller Sauter mean diameter (SMD) of droplets under the non-evaporating condition. Under the evaporating conditions, for the free spray cases, there exists a trade-off between the fuel evaporation and the spray penetration in the application of the group-hole nozzle; with the increase of interval between orifices, the ratio of evaporation increases, however, the tip penetration is restrained. For the spray impinging on a flat wall, the group-hole nozzle can enhance the spray tip penetrations in both view directions compared to the single-hole nozzles, nevertheless, the evaporation improvement effect decreases compared to the free spray case. Flame visualization images show that this enhancement of the fuel atomization and evaporation may contribute to decrease the overall flame luminosity level, indicating the potential of suppressing the soot formation in D.I. diesel engines.