fuel-mixing process. The nozzle geometry and its cavitation tendency must be settled at nozzle characterization studies.

The entire struggle on spray mixing and characterization investigations is related to its autoignition and combustion process. Ignition delay period starts with the injection of fuel and consist physical and chemical delay periods until the autoignition occurs. The process of fuel atomization, evaporation, and mixing with air take place in physical delay period. Then, chemical reactions begin slowly and initiate autoignition. This period is called the chemical delay period. The total ignition delay period is generally expressed by Arrhenius-like equations. According to these different ignition delay equations, the effective parameters on ignition delay are ambient conditions and fuel injection pressures. There are many authors proposed different coefficients for ignition delay equations. Some researchers add new parameters to the ignition delay equations such as, effect of injection pressure and nozzle geometry. It is known that ignition delay time gets shorter as ambient pressure, ambient temperature and ignition pressure increase.

The autoignition location of the diesel spray is also another important research point. Dec combined his studies on diesel spray combustion and proposed a conceptual diesel spray model. His work changed the diesel autoignition understanding. He depicted that ignition occurs progressively at multiple points across the downstream regions of all the fuel jets, beginning well before the start of the premixed burn spike. In the next study of Dec and Espey, autoignition of diesel fuel was investigated. The chemiluminescence imaging results showed that the first detectable soot luminosity in isolated pockets occurs randomly along the sides of the liquid-fuel in the upstream portion of some of the fuel jets.

The nozzle geometry effect on spray development has been widely investigated in the literature. However, the connection between the nozzle geometry and ignition delay has not been extensively investigated yet. In this study, four nozzles were manufactured and their real inlet geometries were