# Limiting Conditions for Droplet Fragmentation of Stabilized Suspension Fuels
## 1 Introduction  
The problems of coal-dependent energy providers around the world are mostly related to high anthropogenic emissions from the combustion of natural solid fuels [1; 2]. A highly potential solution to these problems is based on burning these fuels as part of blends with various additives [3; 4]: water, slimes, heavy coal-tar products, resins, biomass, etc. Each of these additives makes it possible to vary the technological, economic, environmental, and energy performance indicators of power plants fired by composite fuels [5; 6]. In particular, a multicriteria analysis has shown [7; 8] that water-based slurry fuels exceed natural solid fuels in the relative performance parameters. As a result, the so-called composite liquid fuels became widely known [9; 10]. These fuels are commonly classified into coal-water slurries with petrochemicals [11] and without petrochemicals [12; 13]. These fuel types are highly viscous since they normally contain 30% to 60% of solid particles [14]. Hence, the layer structure of such fuels changes quite significantly during their storage in reservoirs and transportation, and so does the structure of jets and separate droplets formed during atomization. This affects the temperature and concentration fields in the combustion chamber, fuel combustion efficiency, environmental indicators of plant operation, etc.  
Composite liquid fuels are notable for solid particle sedimentation and agglomeration in droplets, intensifying the fuel stratification [15; 16; 17]. Emulsified and slurry fuels are conventionally stabilized with the help of a set of additives, with oils, solvents, soy lecithin, and sodium lignocellulosic being regarded as the most promising ones [16; 18]. These stabilizing additives can vary the fuel properties in a controlled manner during storage and transportation. Coal-water slurry fuels generally hold more potential for northern regions with their abundant reserves of natural solid fuels [19]. In this case, the composition of slurry fuels needs to be kept stable at low ambient temperatures, and this is when soy lecithin and sodium lignocellulosic are useful [16; 18]. It remains unstudied how the stabilizing additives to slurry fuels affect the droplet breakup upon intense heating (i.e., the so-called secondary atomization directly in the combustion chamber). Such breakup may proceed in several regimes. Emulsified and slurry fuels typically break up in the puffing regime [20; 21] when liquid fragments break off from the surface of the parent droplet throughout the entire heating time (and fuel droplets are heated for most of their residence time in a combustion chamber). Droplets with immiscible flammable (e.g., diesel, kerosene, rapeseed oil, etc.) and nonflammable (water) components more often exhibit microexplosion [22; 23] to form an aerosol of small fragments within a short heating time. By varying the concentrations of liquid flammable and nonflammable components in droplets, one can change the break-up regimes (from microexplosion to puffing or back), critical conditions (heating times and threshold temperatures), and outcomes (size and number of secondary fragments). It is important to analyze the impact of stabilizing additives to slurry fuels on droplet breakup behavior in a wide range of temperatures. This was the motivation of the present research.  
The aim of this research is to experimentally determine the effect of stabilizing additives to promising slurry fuels (that would prolong their homogeneous structure) on droplet evaporation, dehydration, and breakup behavior in the puffing and microexplosion regimes upon intense heating. Current fundamental results of limiting conditions for suspension fuels droplet fragmentation was based on new methods of preparation stabilized CWS and CWSP fuels [24]. New findings presented in this paper are important in atomization of stabilized fuels inside combustion chambers to increase combustion efficiency alternative types of fuels.