## 2 Experimental Setup and Method
### Materials
It is quite easy to implement and requires no complicated or costly equipment, like it is, e.g., in the thermal processing pelletization [33; 34]. The main idea of this research is to study the influence of the component composition of fuel pellets on the mechanisms and characteristics of their combustion, but not the influence of the fuel pellet production technique on their physical and mechanical characteristics. Therefore, experimental samples were obtained using the cold (25 \({}^{\circ}\)C) pressing method (without additional heating of fuel components or adding binders). In the preparation of compositions No. 2-No. 4 for pressing, FC (90 wt%) was divided into two parts of identical mass. The first part was put into a pellet die. Then a porous polymer material, impregnated with a combustible liquid, was added to it. The second part of FC was put over it in the press die, and the mass was compressed. In the production of compositions No. 5-No. 8, FC (70 wt%) was preliminarily mixed with sawdust (30 wt%) of the corresponding particle size. Then the mixture \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Composition** & **FC** & **Additive** & **Q, MJ/kg** \\ \hline No. 1 & 100\% & – & 24.74 \\ No. 2 & 90\% & 10\%—porous polymer material impregnated with & 26.73 \\  & & rapeseed oil & \\ No. 3 & 90\% & 10\%—porous polymer material impregnated with & 26.05 \\  & & water-oil emulsion (rapeseed oil) & \\ No. 4 & 90\% & 10\%—porous polymer material impregnated with & 26.63 \\  & & water-oil emulsion (turbine oil) & \\ No. 5 & 70\% & 30\%—dry sawdust (particle size of less than 45 \(\upmu\)m) & \\ No. 6 & 70\% & 30\%—dry sawdust (particle size of 45–100 \(\upmu\)m) & \\ No. 7 & 70\% & 30\%—dry sawdust (particle size of 100–200 \(\upmu\)m) & 22.07 \\  & & & & \\ No. 8 & 70\% & 30\%—dry sawdust (particle size of 200–500 \(\upmu\)m) & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Fuel compositions. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Component** & \multicolumn{4}{c}{**Proximate Analysis**} & \multicolumn{4}{c}{**Ultimate Analysis**} \\ \cline{2-10}  & \(\mathbf{A^{\mathrm{d}}}\) & \(\mathbf{W^{\mathrm{a}}}\) & \(\mathbf{V^{\mathrm{daf}}}\) & \(\mathbf{Q^{\mathrm{a}}}_{s\
u}\) & \(\mathbf{T_{\mathrm{ign}}}\) & \(\mathbf{C^{\mathrm{daf}}}\) & \(\mathbf{H^{\mathrm{daf}}}\) & \(\mathbf{N^{\mathrm{daf}}}\) & \(\mathbf{S^{\mathrm{daf}}}\) & \(\mathbf{O^{\mathrm{daf}}}\) \\  & **(\%)** & **(\%)** & **(\%)** & **(MJ/kg)** & **(\({}^{\circ}\)C)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline FC & 26.5 & – & 23.1 & 24.83 & 450 & 87.2 & 5.1 & 2.1 & 1.1 & 4.5 \\ Sawdust & 2.0 & 19.8 & 73.52 & 16.45 & 340 & 50.3 & 6.0 & 0.2 & 0.1 & 43.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results obtained from proximate and ultimate analysis of filter cake (FC) and pine sawdust [12; 28; 29]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Oil** & **Density at 20 \({}^{\circ}\)C (kg/m\({}^{3}\))** & \(\mathbf{W^{\mathrm{a}}}\) (\%) & \(\mathbf{A^{\mathrm{d}}}\) (\%) & \(\mathbf{T_{\mathrm{f}}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{\mathrm{ign}}}\) (\({}^{\circ}\)C) & \(\mathbf{Q^{\mathrm{a}}}_{s\
u}\) (MJ/kg)** \\ \hline Rapeseed oil & 911 & 0.28 & 0.03 & 242 & – & 39.52 \\ Used turbine oil & 868 & – & 0.03 & 175 & 193 & 44.99 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Properties of oils [28; 30]. was compressed to produce fuel pellets. The above size (3 mm in diameter and 3 mm in height) of fuel pellets was chosen intentionally to conduct laboratory experiments considering two main limitations. First, the high-temperature medium of pellet combustion is generated in the rotary muffle furnace, whose dimensions are limited. Second, the fuel pellet combustion duration corresponds to the maximum recording time of the high-speed video camera, used to capture the processes under study.