# Limiting Conditions for Droplet Fragmentation of Stabilized Suspension Fuels
## 4 Results and Discussion
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For instance, no more than 20% of the initial droplet volume puffed in the experiments with the compositions based on filter cake. However, in the experiments with droplets containing water, coal, and a liquid combustible component, more than 90% of the initial droplet volume disintegrated and broke up into an array of small fragments. These processes heavily depended on ambient conditions (air flow temperature and velocity) and droplet sticking to the holder surface. Then, due to boiling and rapid evaporation followed by ignition, a solid crust was formed on the holder surface, which increased  
Figure 8: Temporal characteristics of droplet evaporation and drying until breakup for blends C50W49 LE1 (**a**) and C50W50 (**b**) (\(R_{\text{d0}}\) = 1.3 \(\pm\) 0.1 mm): 1—\(T_{\text{a}}\) = 450 \(\pm\) 30 K; 2—\(T_{\text{a}}\) = 950 \(\pm\) 30 K.  
the surface roughness and the surface area. These conditions intensified heat and mass transfer, phase transitions, and chemical reactions. Such effects do not manifest themselves in real combustion chambers due to the absence of metal holders, but the sequence of processes and phenomena occurring when droplets are injected into combustion chambers and stick to their walls are similar. To minimize these effects, it is important to add liquid combustible components to slurries based on filter cakes and other coal processing wastes. Coal-based slurries are less susceptible to these effects. That is why the injector settings for spraying two- and three-component coal-based mixtures can be varied in a wider range. The critical durations of droplet heating until breakup obtained in this research can help predict the typical distances covered by droplets in combustion chambers. In this research, the initial sizes of fuel droplets were chosen as somewhat larger (1-1.5 mm) than recommended for spraying (as a rule, 50 to 250 \(\upmu\)m) [51] in the combustion chambers of power plants. This is motivated by our commitment to considering all the stages of the processes under study in detail, tracking the patterns of droplet surface deformation, and specifying the contribution of each component to the processes of evaporation, boiling, breakup, and ignition. The experimental data obtained earlier for a wide range of droplet sizes (0.5 \(\upmu\)m to 1.5 mm) [42] and microexplosive breakup models [22] make it possible to predict the critical conditions (in particular, the sufficient temperatures and typical heating durations) for the breakup of droplets with compositions similar to those presented in this research. In particular, if the initial droplet size of coal-water slurries with and without petrochemicals is reduced to 250 \(\upmu\)m, the typical durations of their heating until intense breakup do not exceed 0.5 s. The results of the corresponding predictions are important for determining the composition-specific critical and advisable conditions of intense droplet breakup in combustion chambers. The droplet diameter ratios at different stages of their heating and deformation presented in this research make it possible to predict the variation ranges in the droplet surface area ratios throughout their lifetime. These ratios are important for estimating the intensity of droplet heat exchange in combustion chambers. For instance, it was established that ratio of the surface area of secondary fragments to the initial surface area of the parent droplet was 5-10 for the conditions under study. The maximum value equaled 10 and corresponded to the compositions containing rapeseed oil and coal. These values are clearly lower than those reached by two-liquid droplets without solid particles: 100 to 200 [42]. The main reason is in the fundamental role of solid particles in the droplet composition. These particles agglomerated actively within a droplet due to their high relative concentrations. The resulting agglomerates only broke up after the surface and pore space became significantly drier.