Author: C. BaePublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Diesel injection nozzles, incorporated with common-rail, high-pressure injection system, have the variety in its geometries. The design parameters of injection nozzle need to meet the requirement of compact fuel spread and atomization followed by mixing with air and combustion in HSDI (High-Speed Direct Injection) diesel engines. Diesel injectors with various nozzle geometries were tested to investigate the spray characteristics by optical-imaging techniques. Sac-nozzle and VCO nozzle incorporated with common-rail system were tested to see the behavior 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 was 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 non-evaporative transient diesel spray, such as spray penetration and spray angle were measured from macroscopic images, which were frozen by an instantaneous photography with spark light source and CCD camera. Internal structure during spray development for atomization was analyzed from microscopic images, which was manifested through magnified spray images taken by a long-distance microscope. These provided the better understanding of the spray surface structure and the primary breakup process of dense spray from VCO nozzles incorporated with common-rail injection system. Fuel droplet sizes, mainly represented by SMD (Sauter Mean Diameter) were also estimated from the images. Spray images were taken in a pressurized chamber (up to 30 bar) at various ambient conditions and fuel supply pressures for various nozzle geometries. The spray development from sac-nozzle and VCO nozzle was discussed. The holes with different geometry in nozzles, especially differently tapered holes (0~2 in K factor), were found to give different macroscopic behavior in terms of spray penetration and spray angle and subsequently various atomization performances. Higher K factor and smaller exit hole sizes showed faster penetration, especially at lower ambient pressure, and smaller spray angle.