Effect of Nozzle Geometry on the Common-Rail Diesel Spray 2002-01-1625

Diesel injections with various nozzle geometries were tested to investigate the spray characteristics by optical imaging techniques. Sac-nozzle and VCO nozzle with single guided needle coupled with rotary-type mechanical pump were compared in terms of macroscopic spray development and microscopic behavior. These nozzles incorporated with common-rail system were tested to see the effect of high pressure injection. Detailed investigation into spray characteristics from the holes of VCO nozzles, mostly with double guided needle, was performed. A variety of injection hole geometries were tested and compared to give tips on better injector design. Different hole sizes and taper ratio, represented as K factor, were studied through comprehensive spray imaging techniques.

Global characteristics of a diesel spray, such as spray penetration, spray angle and its pattern, were observed from macroscopic images. Internal structure of the diesel spray development was analyzed from microscopic images. These measurements provided a better understanding of the spray surface structure and breakup process of a dense spray from VCO nozzles incorporated with common-rail injection system. Fuel particle sizes, mainly represented by SMD (Sauter Mean Diameter) were also estimated from the images. All the tests were carried out in a pressurized chamber under various ambient conditions and fuel supply pressures for various nozzle geometries.

The different developments from sac-nozzle and VCO nozzle with both single-guided needle and double needle are discussed. The holes with different geometry in VCO nozzles, especially differently tapered holes characterized K factor (0-2), were found to give different macroscopic behavior in terms of spray penetration and spray angle and subsequently various atomization performances.