macroscopic spray characteristics; autoignition, autoignition sides and flame lift-off length has been carried out by using shadowgraphy technique. The spray tip penetration data were obtained by using a digital imaging program which enables to use the same threshold level to distinguish spray tip from the background and also measure the distance between the nozzle hole and spray tip. A continuous 250 W light source, Dedocool lighting system and an opaque screen were used to obtain shadowgraph images of the spray. A more uniform distribution of the source light on the spray is obtained by using opaque screen placed between the light source and the back window. This opaque screen scatters nonuniform intensity illumination which is at its highest level in the center of the light beam and prevents overexposure which may lead misdetection of less dense, outer and weak edges of the spray shadow.
4.3.3 Nozzles and theirs dimension
To investigate the effect of nozzle geometry, four nozzles were specially manufactured for experiments. Each nozzle has one hole coincided with the nozzle axis. Thus, the injected spray axis also coincides with the chamber axis. The schematic diagram of the injector nozzle is given in Figure 2 and the properties of the used nozzle types are given in 4.3.1.1. They are all have length/diameter ratio of ~4. Hydrogrinding process was performed for Nozzle B and Nozzle D. The nozzle hole diameters are not identical in order to keep the same nozzle flow rate. Except Nozzle A, the flow rates of the nozzles, Q, defined as fuel rate injected at 100 bar are identical.
Conicity of the nozzles is represented by k-factor, which is a parameter indicating the diameter difference of inlet and outlet holes (it is defined as k-factor = (Di −Do)·100). Nozzle A has divergent shape and Nozzle D has convergent shape.
The real dimensions of the test nozzles were obtained by using Nikon LV 150 industrial microscope. Clemex Vision software program was used for