Development of micro-diesel injector nozzles via MEMS technology and effects on spray characteristics

摘要

Micro-machined diesel injector nozzles have been designed,fabricated,and used with commercially produced diesel injection systems in the study of spray dynamics.Such a system,properly designed,may improve spray behavior in direct-injection (DI) diesel engines by improved atomization and fuel-air mixing.In this work,14 micro-planar orifice nozzles were fabricated using the micro-electro-mechanical-systems (MEMS) technique.Circular-orifice diameters were varied from 40 to 260mum,and the number of orifices was varied from one to 169.Three plates with noncircular orifices were also fabricated to examine the effect of orifice shape on spray characteristics.These nozzles were then attached to commercial injectors and the associated injection systems were used for the spray experiments.Given these novel injection systems,jet spray characteristics of micro-planar-orifice nozzles were investigated experimentally using optical diagnostic techniques in a pressurized constant-volume cylindrical chamber.Local drop sizes were measured by the laser diffraction technique,and average drop sizes of the whole sprays were measured by the light extinction technique.Current test results show expected qualitative trends in spray kinematics and drop sizes,but quantitative magnitudes of the behavior are less dependent on orifice geometry than first anticipated.Droplet coalescence among adjacent sprays was apparent for the multiple-orifice nozzles because all the orifices were aligned in the same direction with limited spacing.Nonplanar configurations are under development and may show improved performance.