*3.5. Droplet Driftability*

According to other authors [13,43,56,57,64], the V100 is a valuable parameter to predict spray drift. The lower this parameter, the lower the portion of spray droplets below 100 μm and, therefore, the predicted incidence of the spray drift. As it is displayed in Figure 11, V100 values were generally higher for the cannon-type nozzle in the CP and AP. This trend enhanced the spray drift generation during field spray application, as the cannon spout must spray at a longer distance from the target than the hand one in the conventional setting used in farms (Figure 1b). Nevertheless, the present study showed a different behavior of the two nozzle types in the droplet size spectra increase after the AP (liquid hose out of the spout body). Thus, for OP and XP, cannon spout presented lower V100 values when compared to the hand-type one (Figure 11). This finding might be relevant for the spray drift reduction, as it could indicate a higher interest in implementing OP and XP in the cannon spout.

**Figure 11.** V100 (%) per liquid hose position (HP), liquid flow rate (LFR) and airflow speed (AS) for both the (**a**) cannon-type and (**b**) hand-type nozzles. Bars show the mean ± Standard Error. The dashed lines represent the hydraulic reference nozzles, namely hollow cone conventional ATR lilac in red and air induction TVI 8001 in green (Albuz®), both operated at 0.7 MPa pressure. CP, conventional insertion of liquid hose position; AP, alternative position; OP, out position; XP, extreme position.

Indeed, in the case of the cannon-type nozzle, there was a consistent V100 reduction among consecutive hose positions. Thus, from a mean value of 68% in CP, the V100 mean value decreased to 8% in XP (Figure 11a). Within each liquid hose position, the combination of minimum LFR with maximum AS and maximum LFR with minimum AS deeply affected the driftability. These settings yielded mean V100 values of 49 ± 2% (max LFR/ min AS) and 61 ± 2% (min LFR/max AS) in CP (Figure 10a). AP gave V100 results between 21 ± 1% (max LFR/ min AS) and 64 ± 2% (min LFR/max AS). OP resulted in a range from 10 ± 1% (max LFR/ min AS) to 21 ± 1% (min LFR/max AS). Finally, XP values ranged from 5 ± 1% (min LFR/ min AS) to 10 ± 1% (min LFR/max AS) (Figure 10a). In a practical way, the best V100 reduction within each hose position was always achieved when the system was operated with the maximum LFR and minimum AS, confirming the marked influence of these operational parameters [53].

Comparing V100 values generated by pneumatic nozzles with those generated by the reference hydraulic nozzle (Figure 11a) Albuz® ATR lilac operated at 0.7 MPa pressure (dashed red line corresponding to V100 equal to 74%), it can be observed that similar values were obtained when the pneumatic nozzles were used in CP and combined with the highest AS (89.6 and 97.7 m s<sup>−</sup>1). Changing the hose position from AP to XP, all possible combinations of tested parameters reduced the V100 level compared with the reference nozzle. This finding reflects the capability of AP, OP and XP to generate droplet populations with a driftability similar to those produced by a wide range of conventional hydraulic nozzles characterized by different dimensions and operated in a wide range of liquid pressure. Specifically, the V100 values for XP were similar to those obtained using hydraulic air induction nozzles. Indeed, the cannon-type nozzle operated in the XP position and, combined with the lowest AS, achieved V100 values fully comparable with those obtained with air induction nozzle Albuz® TVI8001 (V100 equal to 4%) marked with the dashed green line in Figure 11a. The minimum value achieved in the XP was 5%, so the droplet size can be considered similar to that of a conventional low-drift nozzle. Considering the configurations characterized by the combination of highest AS (97.6 m s −1) and highest LFR (2.67 L min−1), the switch of HP from CP to XP determined a reduction of V100 equal to 90%, a value fully confirmed by field trials that showed a 95% reduction in off-target losses [58].

Regarding the hand-type spout, there was a significant reduction in V100 across the different hose positions, turning from a mean value of 58% in CP to 9% in XP (Figure 11b). Nevertheless, there was a low reduction between AP and OP. Indeed, the mean V100 value only decreased from 29% to 28%. The lowest possible value in the conventional nozzle configuration was 37 ± 1% for the maximum LFR with the minimum AS (Figure 11b). AP originated values between a maximum mean value of 53 ± 3% (med LFR/max AS) and a minimum of 8 ± 2%. OP yielded values between 56 ±1% (min LFR/max AS) and 16 ± 1% (max LFR/min AS). Finally, XP resulted in values from 22 ± 1% (med LFR/max AS) and 3 ± 1% (min LFR/min AS) (Figure 11b). Comparing these values with the reference nozzle Albuz® ATR lilac operated at 0.7 MPa pressure (V100 equal to 74%), only the liquid hose in CP combined with the highest AS generated values higher than the threshold marked with a dashed red line in Figure 11b. Concurrently, the liquid hose in XP combined with the lowest AS was able to lower the V100 threshold fixed by the reference air induction nozzle Albuz® TVI8001 marked with the dashed green line in Figure 11b. The very low V100 values achieved in the last position of the liquid hose were even lower than many of the ones reported for the hydraulic low-drift nozzles [43]. Even if the V100 values measured in this study (74%) for the Albuz® ATR lilac operated at 0.7 MPa pressure were higher than those obtained by Zande et al. [43] (equal to 23%), the droplet size spectra parameters were fully in accordance with those reported by ASABE S572.1 classification, and the nozzle falls in the same class, namely very fine (VF) [63].

As it can be drawn from Figure 12, there was a clear correlation between V100 and D50 in both cases (*p* < 0.001). Determination coefficients were very similar (0.9764 and 0.9704 in the cannon-type (Figure 12a) and hand-type (Figure 12b) nozzles), and the correlation coefficients were nearly the same (−0.01 and −0.009). This result indicates that both nozzles have similar behavior. Moreover, this kind of response can be expected from different pneumatic nozzles. In the case of the cannon, there was a deviation of the regression line with high D50 values. This behavior can be expected when taking into account the higher variability that is found in the most extreme positions of the liquid hose (Figure 12a). A similar trend can be noticed in the hand nozzle for which a loss of fitting in the lowest D50 values can be observed (Figure 12b).

**Figure 12.** Correlation between D50 (μm) and V100 (%) for all tested configurations (combination of liquid hose insertion position (HP), liquid flow rate (LFR) and air speed (AS) for both the (**a**) cannon-type and (**b**) hand-type nozzles.
