## 3 Results and Discussion
### How Accurate Are Transition Criteria? In an attempt to assure the universality of these empirical correlations establishing a boundary between the spreading and splashing regimes for a single droplet impact upon a wetted surface, the phenomena obtained in these experimental results were compared with the phenomena predicted by these transition criteria. The validation ranges were carefully applied to the results obtained and Figure 12 shows info-graphics identifying the accuracy of the different transition criteria in comparison to the experimental results. In these graphs, the impact conditions are identified, being the fuel mixtures described by its concentration of jet fuel. The increase of droplet initial diameter (\(D_{0}\)) and droplet impact velocity (\(U_{0}\)) are established by the arrows. The agreement of the experimental results and the criteria were described by a color scheme. Black represents the cases where the phenomena obtained experimentally agree with the criteria, white displays the cases where the phenomena obtained experimentally do not agree with the predicted outcome, and grey defines the cases outside the validation range of empirical correlations. The validation range of the [PERSON] and Gosman [4] empirical correlation for sorting the splash event, fits a small part of our data. Namely, it predicts the outcome of pure water and 100% jet fuel, agreeing 100% with the results obtained experimentally. The transition criterion proposed by [PERSON] et al. [5] is the only one that considers the influence of the liquid film thickness. Additionally, the experimental data used to define this correlation include experiments with a wide range of liquid film thicknesses. Similar to the previous criterion, it only fits part of our data. The outcomes of both fuel mixtures can be predicted by this correlation. Considering all the cases within the validation range, 78% are correctly predicted by the criterion, failing mainly for the higher liquid film thicknesses. The [PERSON] and [PERSON] [6] empirical correlation considered includes a random element in the determination of the mass ratio. This value was assumed as \(\eta=1\) and compared to the experiments within its validation rate. The only fluid that can not be predicted by this correlation is H\({}_{2}\)O. This criterion predicts correctly 80% of the cases. It failed only for the higher droplet diameters for 75% JF-25% HVO and the smaller impact velocities, and for the smaller diameters of both mixtures with the increase of the impact velocity. However, for the higher impact velocity, all cases within the validation range fit the same result as the criterion predicts. The final transition criterion of [PERSON] et al. [7] is the most recent and it was defined using experiments of single droplets impinging only on thin liquid films. Therefore, it only fits our experiments for the thinner dimensionless liquid film thickness (\(\delta=0.1\)). The criterion predicts 95% of the experiments correctly. It only failed on the larger diameters for the fuel mixtures for the lower impact velocities. If we restrict the use of these correlations to their validation range, the criterion that better predicts the outcome of drop impact on wetted surfaces, with the fuels and alternative fuels used in the experiments, is the one formulated by [PERSON] and [PERSON] [4] because it fitted 100% of the experimental results obtained. Both [PERSON] et al. [5] and [PERSON] and [PERSON] [6] have a similar prediction accuracy. The criterion defined by [PERSON] et al. [5] is the only one that considers the influence of the liquid film thickness, yet, its prediction capability decreases for higher Reynolds numbers and high dimensionless film thicknesses. Finally, [PERSON] et al. [7] focus its boundary on thin liquid films. Its accuracy is high, failing only for the larger droplet diameters for both mixtures. As follows, the assumption that a liquid film behaves as a very rough surface is, in fact, valid and [PERSON] et al.