# Limiting Conditions for Droplet Fragmentation of Stabilized Suspension Fuels
## 4 Results and Discussion
### Droplet Behaviors
The inflow of volatiles also intensified the increase in the gas-vapor mixture pressure around the droplet, which limited the heating and vaporization rates. Changes in the air flow velocity near the particles of composite fuels also exhibited a significant impact on their heating and breakup behavior. A transition from natural to forced convection intensified the heat exchange near the droplet surface, accelerated its heating, causing small solid particles to break off from the surface and the droplet to deviate from a spherical shape. These processes contributed to leveling out the temperature field of a droplet; there were fewer local superheating zones. As a result, microexplosions occurred very rarely, and puffing was observed in most cases. However, if an air jet with a moderate temperature flowed around a droplet, its near-surface layer was dried, large agglomerates of solid particles fractured in this layer, and the particles were entrained from the surface. Such conditions are considered highly ineffective at intensifying droplet breakup to provide the secondary atomization of composite droplets. The initial size of liquid droplets significantly affects their breakup regime and outcomes. This factor also manifested itself in the experiments. In particular, the liquid steadily evaporated from the near-surface layers without breakup in a wide temperature range when the droplets were less than 1 mm in size. With an initial droplet size of more than 1.5 mm, the shape of such droplets deformed considerably within a short period of time. The position of such a droplet became unstable. It broke off from the holder to fall under gravity. Droplets of different component composition broke up when heated only if their initial size fell into the range of 1 to 1.5 mm. These patterns are typical of two- and multi-component droplets. They correlate well with earlier established patterns for two-liquid droplets breaking up in the puffing and microexplosion regimes [42]. [PERSON] et al. [31] analyzed how the holder and the schemes of droplet placement on it affected the microexplosive breakup delay and outcomes. They established that the lower the temperature of the heating medium and the smaller the initial droplet size, the greater this impact. They compared the contribution of different holder materials to droplet heating until its microexplosive breakup. A nichrome wire, 0.5 mm in diameter, provides the minimum interference (compared to steel, iron, ceramic, and other holders). This is the holder that we used in the present research. Another important pattern that was not mentioned in the earlier research [31] manifested itself in the experiments with droplets containing solid particles: the particles settled on the holder surface, and even more so when heated. That is why it was necessary to minimize the droplet residence time on the holder surface before introducing it into the heated gas. It was important to intensify droplet heating before significant changes in their structure due to solid particle sedimentation and agglomeration on the holder surface. The impact of this factor could be easily observed when monitoring the experimental data scattering in terms of the breakup delay time and secondary fragment size. If these characteristics scattered by more than 15-20% relative to the average values, it was necessary to shorten the droplet residence time on the holder. A major effect on solid particle sedimentation and agglomeration on the holder surface comes from the stabilizer used in the experiments. All the stabilizers we used minimized the sedimentation of solid particles, but the duration and scale of their influence differed. For instance, the positive effect of diesel fuel and oil for multicomponent droplets only lasted a short time: droplet stratification and solid particle sedimentation began 30-40 min after the droplets were produced. When adding soy lecithin or sodium lignocellulosic, droplet stratification was not observed for several days.