## 3 Results and Discussion
### Enhancement of Fuel Ignition  
From experiments, the main significant factors (properties of liquid components, concentrations of solid and liquid components) that affect the implementation of droplet dispersion under intense heating conditions were established. For the group of compositions: coal + oil + water + highly flammable liquid (gasoline, diesel fuel, kerosene, formic acid), the ignition and dispersion characteristics of 2 mm droplets were obtained at one initial fuel temperature \(T_{0}\) = 20 \({}^{\circ}\)C and one heating source temperature \(T_{g}\) = 900 \({}^{\circ}\)C. Two groups of fuel compositions (Table 5) differ in oil concentrations (in both groups, the mass fraction of coal is the same and equal to 40%): the 1 st group contains 15% rapeseed oil and 45% water, and the 2 nd group contains 40% rapeseed oil and 20% water. In addition, 5%highly flammable liquids (HFL) were added to the basic fuel compositions of both groups. Their main characteristics are given in Table 6.  
Figure 7 shows typical video frames of ignition and combustion of considered composite fuels (Table 5) at one typical initial fuel temperature \(T_{0}\) = 20 \({}^{\circ}\)C in high-temperature air at \(T_{g}\) = 900 \({}^{\circ}\)C.  
There are different dominant ignition and combustion mechanisms in the two groups of composite fuel compositions due to the different mass ratio of their components (Table 5). It is guaranteed that the fuel droplet disperses both during ignition and burnout (Figure 7) at an oil:water ratio of 1:3 (1 st group). When the oil:water ratio is 2:1 (2 nd group, the droplet moderately disperses, predominantly during the ignition process, with the gas-phase combustion mechanism of the components predominating (Figure 7). The addition of highly flammable liquids to fuel compositions (gasoline, diesel fuel, kerosene, formic acid) with a concentration of 5% wt. influences the patterns and characteristics of the process under study. The averaged ignition delay times for composite fuels with and without HFL are presented in Figure 8.  
Based on the results obtained, it can be concluded that the concentration of the main combustible liquid (rapeseed oil) significantly affects the ignition delay times. With an increase in concentration from 15% to 40% (No. 21 and No. 31), due to a decrease in the concentration of the liquid non-combustible component (water), the ignition delay times decrease by a factor of 2.3. For the 2 nd group's compositions that contain 40% of the main combustible liquid, the addition of 5% HFL does not significantly affect the change in the ignition delay time due to the high concentration of the volatile component. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Liquid**} & **Boiling** & **Point** & **Fash Point** & **Self-Bignition** & **Lateral Heat of** & **Solubility in Water at** & **Water at** 20 \({}^{\circ}\)C, kJ/kg** & **Solubility in** **20 \({}^{\circ}\)C, kJ/kg** & **Water at** \\  & **Point** & \({}^{\circ}\)C & & \({}^{\circ}\)C & & 20 \({}^{\circ}\)C, kJ/kg** & **20 \({}^{\circ}\)C, kJ/kg** & **20 \({}^{\circ}\)C, kJ/kg** & **20 \({}^{\circ}\)C, g/100 mL** \\ \hline Gasoline & 20–200 & \(-\)21 & 250 & 290–300 & none \\ Diesel & 282–338 & 52 & 254–285 & 230–250 & 0.0005 \\ Kerosene & 150–290 & 66–67 & 220 & 250–270 & 0.15 \\ Formic acid & 101 & 69 & 520 & 433–502 & miscible \\ Rapeseed oil & 201–344 & 244 & 318 & 916 & none \\ Turbine oil & 311 & 175 & 193 & 167–209 & – \\ \hline \end{tabular}
\end{table} 
Table 6: Main characteristics of highly flammable liquids [38; 39; 40; 41; 42].