| Popis: |
Due to world trend on the emission regulations and greater demand of fuel economy,the research on advanced diesel injector designs is a key factor for the next generation diesel engines. For that reason, it is well established that understanding the effects of the nozzle geometry on the spray development, fuel-air mixing, combustion and pollutants formation is of crucial importance to achieve these goals.In the present research, the influence of the injector nozzle geometry on the internalflow characteristics is studied. For this purpose, ten single-hole diesel injectors differingin the orifices degree of conicity (five cylindrical, five conical) but with similar nozzleflow capacity have been characterized geometrically (measurements of nozzle outletsection) and hydraulically. The mass flow and momentum flux rates have been measured for a wide range of experimental conditions. Special attention is given to study the cavitation phenomenon since the cylindrically-shaped nozzle orifices areexpected to propitiate cavitation due to abrupt changes in flow direction. The study hasbeen carried out with two different fuels: n-Dodecane and commercial diesel, therebythe effect of the fuel properties is also analyzed.The results show that the measured nozzle outlet diameters are higher than the nominalspecification for both nozzle types. As expected, the onset on cavitation on thecylindrical nozzles has been identified causing a reduction on the injected mass for all tested conditions. The effective diameter for the cylindrical nozzles have been found tobe around 180 μm (geometrical diameter ~212 μm) and around 190 μm (geometrical diameter ~191 μm) for the conical ones. Finally, the higher density of Diesel with respect to n-Dodecane have resulted on mass flow rates around 8% over the n-Dodecanevalues for the same test conditions. |
