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

Micromachined planar orifice nozzles have been developed using MEMS (micro-electromechanical systems) technology and tested with commercially produced diesel injection systems. Such a system, properly designed, may have the capability to improve the spray characteristics in DI diesel engines due to improved atomization and fuel-air mixing. To demonstrate this process, 14 microplanar orifice nozzles were fabricated with deep X-ray lithography and electroplating (LIGA) technology. The circular orifice diameters were varied from 40 to 260 microns and the number of orifices 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 diesel injectors and the associated injection systems were used in the study of drop sizes. The experiments were carried out at two different injection pressures (around 25 MPa and 80 MPa). Local drop sizes were measured by a laser diffraction technique, and the average drop sizes of the whole sprays were measured by a light extinction technique. The drop sizes were found to depend primarily on the total mass flow area. Coalescence droplet collisions among adjacent sprays were apparent for the multiple orifice nozzles. Nonplanar configurations are under development and may show improved performance.