*5.4.7 The conceptual model*

The typical conceptual model is used to explain full spray combustion during mixing-controlled phase towards the end of fuel injection, **Figure 8**. The model is a modification of the last stage in jet development captured about 10.0° ASI and to

**Figure 8.** *Zones of Dec's conceptual model [29].*

highlight the peripheral turbulent combustion. For the developed jet, the entrainment of turbulent air vaporize all liquid fuel after some distance from the nozzle tip leading to the formation of uniform fuel-air mixture. This is made up of fuel rich mixture and PAHs which afterwards, burn to generate small soot particles that fills and extends the jet length. The soot concentration and sizes increase downstream in a length referred to as 'plume stem' towards the leading edge and larger particles recirculate within the vortex. In the course of vortex recirculation, some soot particles reach peripheral flame front where they are further oxidized by OH radicals. Descriptively (using the same color codes as in **Figure 5**), the conceptual model could therefore be visualized as having four main zones: the lift-off length, the premixed zone, the plume stem and the vortex head [29]. The emissions and other contributions associated with combustion processes are still the subject of many further investigations.
