# Limiting Conditions for Droplet Fragmentation of Stabilized Suspension Fuels
## 3 Experimental Technique  
The intense breakup of slurry fuel droplets can be provided using different heating schemes with the dominating convective [31; 32], radiative [33], conductive [34; 35], or mixed [36; 37] heat exchange. Droplet microexplosion occurs after the longest heating time in a tubular muffle furnace (model reactor or combustion chamber of a power plant) \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sample** & **W\({}^{a}\), \%** & **A\({}^{d}\), \%** & **V\({}^{daf}\), \%** & **Q, MJ/kg** & **C\({}^{daf}\), \%** & **H\({}^{daf}\), \%** & **N\({}^{daf}\), \%** & **S\({}_{i}\)\({}^{d}\), \%** & **O\({}^{daf}\), \%** \\ \hline filter cake & – & 26.46 & 23.08 & 24.83 & 87.20 & 5.090 & 2.05 & 1.022 & 4.46 \\ bituminous coal & 2.05 & 14.65 & 40.19 & 29.76 & 79.79 & 4.486 & 1.84 & 0.868 & 13.016 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ultimate and proximate analysis of filter cake and coals. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Short** \\ **Name** \\ \end{tabular} } & \multicolumn{6}{c}{**Components**} \\ \cline{2-9}  & **Filter Cake** & **Bituminous Coal** & **Water** & **Sodium Lignosulfonate** & **Diesel** & **Rapeseed Oil** & **Soy Lecithin** \\ \cline{2-9}  & **wt.\%** & **wt.\%** & **wt.\%** & **wt.\%** & **wt.\%** & **wt.\%** & **wt.\%** \\ \hline K50W49L11 & 50 & – & 49 & 1 & – & – & – \\ K50W49P1 & 50 & – & 49 & – & 1 & – & – \\ K50W49R1 & 50 & – & 49 & – & – & 1 & – \\ K50W49L1 & 50 & – & 49 & – & – & 1 & – \\ K50W50 & 50 & – & 50 & – & – & – & – \\ \hline C50W49L11 & – & 50 & 49 & 1 & – & – & – \\ C50W49D1 & – & 50 & 49 & – & 1 & – & – \\ C50W49R1 & – & 50 & 49 & – & – & 1 & – \\ C50W49E1 & – & 50 & 49 & – & – & 1 & – \\ C50W50 & – & 50 & 50 & – & – & – & – \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Slurry fuels used in the experiments. compared to the conductive droplet heating on a substrate [38]. However, the longer the heating time, the more secondary fragments with minimum sizes are produced [39; 40]. Previous research has shown [41] that microexplosion and puffing occur in any of the above heating schemes but in certain temperature ranges depending on droplet composition, type, size, and heating rate [42]. The characteristics of secondary fragments can be recorded using high-speed cameras [39; 43; 44]. The heating scheme affects the velocities and trajectories of secondary fragments and, hence, the accuracy of recording their main characteristics (number, size, velocity, trajectory, momentum, component composition, etc.). An alcohol burner flame was used as the heating scheme for slurry fuels in this study. The analysis of the findings in Ref. [33] shows that parent droplets should be heated in flames to provide the most accurate monitoring of the number, size, velocity, component composition, and energy of secondary fragments. When heated in flames, parent droplets break up into the greatest number of secondary fragments compared to droplet heating in a muffle furnace, on a substrate, or in a heated air flow [33]. That is why this was the scheme of choice for the present research (Figure 1). The burner flame heating scheme simulates the wildfire conditions and combustion chamber conditions where radiant heat exchange prevails. The high-temperature flame zone was created with the help of a burner based on ethanol (maximum temperature: 1150 K) (Figure 1). The temperature in the flame of the alcohol burner was recorded using a system featuring a National Instruments data collection module and fast thermocouples with a measurement accuracy of at least \(\pm\)3 K and a response time of less than 0.1 s. To calibrate the system, the flame temperature was measured in several sections at different distances with an increment of 0.5 cm from the burner. The temperature measurement scheme and data are given in Figure 1b. The droplets were introduced into the test zone using a positioning mechanism with a holder--a nichrome wire, 0.2 mm in diameter.