a continuous liquid core extending from the orifice of the injection nozzle (Figure 2.4.1).

Figure 2.4.1: Pressure-atomised spray near the nozzle tip region

The detaching of the liquid core into ligaments or large droplets is called primary break-up, which involves the action of forces internal to the liquid jet. The liquid ligaments and large droplets will further break-up into small droplets due to the interactions between the liquid ambient gas or droplet collisions. The process of this further break-up is called secondary break-up. The near nozzle region, where the volume fraction of the liquid is usually larger than that of the ambient gas is called the dense spray region. Correspondingly, the downstream region where the volume fraction of the liquid is relatively low is called the dilute spray region.

2.5 Conclusion

An experimental study on the Diesel spray characteristics was performed with an advanced direct injection system (common rail injection system). High speed photography was employed to record the transient high injection pressure Diesel sprays in a rapid compression machine (Proteus). For the study of the spray, the images taken with a high speed video camera were processed and analysed. The results include the analysis of the time delay, the initial spray hesitation, the