Numerical Simulation On Effects Of Injector Nozzle-Hole Layout On Combustion And Emissions In A DI Diesel Engine

It is well known that the atomization and evaporation of the fuel plays a key role in the diesel combustion and emissions. Good atomization is a prerequisite for high efficiency combustion. Multi-hole nozzles with small orifices have been proved to have significant improvements for the diesel combustion and emissions. However, the experiment proved that the small orifice nozzle have unsatisfactory performances under large equivalence ratio, high speed and heavy load conditions because the formation of small spray droplets by the small orifices nozzle not only promotes the atomization, but also reduces the momentum of the droplets and decreases the spray tip penetration. Research has showed that spray tip penetration is a crucial factor under high-speed heavy load operating conditions. In order to keep adequate spray tip penetration in the base of reducing the orifice diameter, group-hole nozzle is proposed by some researchers.In addition to group-hole nozzles, there are some related researches about two-spray-angle nozzle. The three-dimensional model is built based on the parameters of the CY6102BZLQ diesel engine, and its validation is also validated. Five nozzle-hole layouts are designed in this research, including the conventional hole, multi-hole, group-hole, two-spray-angle hole and two-spray-angle group-hole. Combustion and emissions in a working DI engine are studied under this five nozzle-hole layout conditions using three-dimensional simulation process. Further study is done about the combustion and emissions under different inter-hole spacing and included-angle of group-hole nozzles and two-spray-angle hole nozzle. Some parameters are also investigated to understand their influences on the combustion and emissions under five nozzle-hole layout conditions.Some conclusions can be made from the simulation results. The spray from the group-hole nozzle has almost the same spray tip penetration as one from the conventional hole nozzle, but the spray from the multi-hole nozzle has a shorter spray tip penetration. The group-hole nozzle has higher flow rate caused by the spray, and that is why the group-hole nozzle has a longer spray tip penetration. The changes of the inter-hole spacing and included-angle of group-hole nozzle and two-spray-angle hole nozzle are actually the competition between the spray cone angle and spray tip penetration. Under a variety of operating conditions and boundary conditions, the two-spary-angle hole and two-spary-angle group-hole have the highest peak cylinder pressure, but also have higher NOx emission and lower Soot and CO emissions among five nozzle-hole layouts. The multi-hole nozzle has unsatisfactory performance of combustion and emissions under high speed, heavy load, low oxygen concentration and large swirl ratio conditions. Because of the small-bore combustion chamber, the advantages of long spray tip penetration of the group-hole nozzle is not obvious, but compared with the conventional nozzle, it still has some definite advantages.