## 3 Results and Discussion
### Secondary Atomization Mechanisms  
Regarding the obtained outcomes, firstly, they were divided into splashing and non-splashing. There were also two cases, corresponding to jetting without the previous production of secondary droplets by splashing, that did not fit this distribution. Some authors argue that jetting alone should be considered as splashing, but others allege that splashing involves the physical separation from the immediate impact site. Taking that into account, in this study, jetting alone was treated as a special outcome. For heights above 0.5 m, splashing always occurred, but for the lower height (\(z_{1}=0.175\) m), the occurrence of splashing depended on the fluid physical properties, the droplet diameter, and the dimensionless thickness of the liquid film. Despite the splashing and non-splashing division, it is relevant to catalog the phenomena observed for all sets of impact conditions, and identify the differences and similarities between them. Due to the wide variety of impact conditions, Figure 8 presents a scheme with the obtained phenomena depending on the fluid and Weber Number. The phenomena were identified by the initials: NS--non-splashing; S--splash; J--jetting; B--bubble encapsulation. It is important to emphasize the qualitative character of the analysis of the visualized impact mechanisms. Therefore, the descriptions focus on the differences between the several cases observed. For the smaller impact heights (\(z_{1}\)), the outcomes of both H\({}_{2}\)O and 50%/50% mixture droplets did not show splashing for all the impact conditions tested. Therefore, the 50%/50% mixture had formation of fingers at the top of its rim. It was not possible to produce dimensionless liquid films of \(\delta=0.1\) for H\({}_{2}\)O due to the non-wettable behavior of the system water and perspex. In this way, the thinner liquid film for the H\({}_{2}\)O impacts had higher values than \(\delta=0.1\). That fact should not be neglected since the occurrence of splashing is enhanced by thin liquid films [19]. It was also verified that the final spreading diameter is larger for H\({}_{2}\)O, as shown in Figure 9. This supports the assumption that fluids with lower viscosities cause larger final spread diameters [19]. Spreading diameter is clearly influenced by viscosity and its effect increases with time. For the drop impacts closer to the surface, the 100% JF and the 75%/25% mixture showed splashing, non-splashing, and jetting. The jetting episodes were isolated, as mentioned above, and happened for similar impact conditions, with the ejection of a single large droplet after the breakup of the central jet (\(We\approx 310\) and \(\delta=1\)). The Jet A-1 exhibited splashing for the three dimensionless thicknesses, while 75% JF/ 25% HVO did not for \(\delta=1\). Considering the cases where splashing occurred, crown splashing was the only phenomenon spotted for the droplet impingement upon the thinner  
Figure 8: Scheme of the phenomena obtained for the different fluids depending on the Weber number (NS—non-splashing; S—splash; J—jetting; B—bubble encapsulation). liquid films. The secondary droplets produced by prompt splashing are likely to be smaller than the image resolution for a proper characterization. For the impact upon liquid films with \(\delta=0.5\), only prompt splash, or prompt and crown splashing combined were identified, and the secondary droplets were smaller than in the previous case. In the impact with the thicker liquid films (\(\delta=1\)), only one set of conditions produced secondary atomization (100% JF and \(D_{n}=0.84\) mm) through prompt and crown splash, with the ejection of few and tiny droplets. For the middle impact height tested (\(z_{2}=0.5\) m), splashing was always an observed outcome. Crown splashing and jetting occurred for all the fluids and the two mixtures resulted in prompt splash. Moreover, the impact upon thin liquid films produced crown splashing for a set of impact conditions and for all fluids.