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 injector with VCO nozzle which has the tapered injection hole, represented by K factor, was tested to investigate the spray characteristics by optical imaging techniques and LDV 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. Entrainment of ambient gas in a diesel spray was measured by LDV technique. Spray characteristics and entrainment experiment were taken in a pressurized chamber (up to 30bar) at various ambient conditions and fuel supply pressures for taper nozzle geometries.
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. Higher K factor showed faster penetration and smaller spray angle.
Entrainment rate increased with the distance from the nozzle. The rail pressure and density of surrounding gas had an effect on entrainment rate. But K factor(taperedness) did not affect entrainment rate.