In the SF flame Fig upper part it is possible

In the SF flame, Fig. 6 (upper part), it is possible to note that soot starts being detected when surface growth becomes important. Following the streamline, i.e., moving from the flame front toward the stagnation plane (from left to right in the figure), the surface growth becomes even more important, while the GDC-0449 is negligible. This shows that the oxidation cannot affect the final size of the soot particles, which in fact grow reaching a maximum on the stagnation plane. Oxidation is important close to the flame front where soot is present at very low concentration. The model predicts a significant inception rate on the fuel side which suggests that formation of new particles occurs also in this region, in agreement with previous studies [20], [21] and [22].
In the SFO flame, the reaction rate analysis shows a different situation. Particles start being formed very close to the fuel nozzle exit. The small amount of oxygen added in the fuel stream helps to increase the reactivity in this zone and induces a fast growth rate. Oxidation takes place where the formation process is still active. Oxidation by OH is present but it remains quite smaller respect the surface growth. Moving from 2 to 4 mm particle volume fraction rapidly increases. Finally, at the location of the maximum 'GDC-0449' soot concentration the oxidation rate become predominant and soot starts being effectively oxidized. At this point O2 promotes particle and aggregate fragmentation. Fragmentation is probably active even before the maximum soot concentration is reached. In fact, the presence of fragmentation makes the size of particles very small so that the fragmentation rate of particles is even higher than fragmentation rate of aggregates.