## 3 Results and Discussion
### Comparison of Secondary Atomization Methods
It is clear in Figure 10 that  
Figure 10: Effect of liquid properties on the transition boundary between agglomeration and stretching separation during the collision of a droplet with a particle (**a**), with another droplet (**b**) [45] and with a solid substrate (**c**): 1, 2—water; 3, 4—50 vol% water and 50 vol% glycerol; 5, 6—10 vol% water and 90 vol% diesel; 1, 3, 5—stretching separation; 2, 4, 6—agglomeration. the curve separating agglomeration and stretching separation illustrates a steady growth with an increase in the Oh numbers. Therefore, the form of the boundary (namely, the necessary and sufficient conditions for the transition from one regime to another) on the We(Oh) map can be expected to be the same for any other liquid compositions with varying dynamic viscosities, densities, surface and interfacial tensions. The experimental research findings presented in this study for the collisions of liquid droplets with solid substrates at varying liquid properties are consistent with the data and conclusions drawn in [57], where coal-water fuels were the investigated liquids. Similarly to [57], a twofold decrease in the surface tension of liquid was found to reduce the critical Weber number between agglomeration and stretching separation almost by 30-40% and increase the number of child droplets 5-7 times. Lowering the interfacial tension makes it possible to decrease the critical Weber number by 35-40% and increase the number of child droplets 5-6 times. An increase in the liquid viscosity from 1 to 6.3 mPa-s in the collision of a droplet with a substrate [57] results in larger child droplets in the same way as it does in the collisions of droplets with each other and with a solid particle. This reduces the number of secondary fragments almost by 10-15%. An increase in the liquid viscosity also shifts the boundary between agglomeration and stretching separation towards 20-30% higher Weber numbers. Figure 11 attempts to present the regime maps of interaction of droplets with each other (Figure 10b), with a solid particle (Figure 10a) and substrate (Figure 10c) when using such similarity criteria as the Reynolds and capillary numbers. The analysis of the conditions and ranges of the key liquid property variations makes it possible to identify the ranges of consistent occurrence of each of the interaction regimes. For that, the research findings were generalized in the form of Re(Ca) regime maps. Depending on Ca and Re, transitions from agglomeration to stretching separation were recorded. It was established that at high Ca and Re, stretching separation occurs consistently. Collision regime maps in the We(Oh) and Re(Ca) coordinates make it possible to determine the Oh, Ca, Re and We variation ranges (Figures 10 and 11) for agglomeration and stretching separation. These numbers make it possible to factor in the inertia, viscous friction and surface tension forces. Such parameter of liquid as dynamic viscosity was found to have a significant effect on the critical Reynolds number. A rise in the dynamic viscosity reduces the Reynolds number for the transition from agglomeration to stretching separation for all the collisions schemes under study. For instance, an increase in viscosity from 1.0 to 6.3 mPa-s reduces the critical Reynolds number by 10-20%. The analysis of the obtained capillary numbers revealed that a twofold decrease in the liquid surface tension increases Ca by 15-25% in the transition from agglomeration to stretching separation for all the three schemes of droplet collisions. Figure 11: _Cont._  
Studies into the interaction of liquid droplets with a solid particle are associated with certain challenges in conducting experiments. These are generation of micron-sized droplets and particles, providing conditions that are closest to industrial plants (in temperature, pressure, etc.) This makes it necessary to change from experiments over to mathematical modeling of the interaction between liquid droplets and solid particle.