## 2 Experimental
### Characterisation  
The tribological experiments were conducted on an engine cylinder liner-piston ring tribometer (ECPT) assembled by the Institute of Tribology of Hefei University of Technology. The upper and lower cylinders were attached to the tester at a length of 122 mm, width of 15.6 mm, and height of 6.3 mm. The piston ring was 8 mm long and 2 mm wide. Although the tests were conducted at room temperature (approximately 25 \({}^{\circ}\)C), they had already been proven effective at achieving meaningful approximations of actual working engines [18; 19; 20]. Figure 1 presents a schematic of the ECPT. The oil samples were placed in an ultrasonic bath for 30 min before the tribological tests to improve the mixture of fuel and lubricating oils. The wear and friction properties of the oil samples were tested at a load of 210 N and a reciprocating frequency of 10 Hz for 6 h. The sliding distance of the piston ring was 80 mm and the speed of oil supply was 25 mL/h. The electrical signal denoting pressure \begin{table}
\begin{tabular}{c c c c} \hline \hline
**RT (min)** & **Area (wt\%)** & **Composition** \\ \hline
4.51 & 0.74 & 5H-furan-2-ketone \\
4.76 & 1.31 & 2,3-Dimethyl-central ethanol \\
5.19 & 0.38 & 3-Methyl-5H-furan-2-ketone \\
6.15 & 1.18 & Maple lactone \\
6.59 & 1.57 & Phenol \\
6.8 & 1.12 & O-Methyl phenol \\
7 & 1.46 & Cresol \\
7.79 & 1.78 & 2,6-Dimethyl phenol \\
8.99 & 1.14 & 3,4-Dimethyl phenol \\
9.7 & 1.31 & 4-Ethyl-phenol \\
10.1 & 1.53 & 3-(2-hydroxyl-phenyl) acrylic acid \\
10.81 & 3.53 & Catechol \\
11.9 & 1.36 & 3-Methyl catechol \\
12.7 & 0.24 & Vanillin \\
12.86 & 0.71 & 4-Ethyl catechol \\
14.73 & 9.95 & Fructose \\
15.5 & 0.20 & 2,3,4-Trimethoxy benzaldehyde \\
15.8 & 0.15 & 3-(4-hydroxyl-2-methyl-phenyl) acrolein \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._ \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Items** & **DO** & **CBF** & **EBF** & **FFEO** & **Methods** \\ \hline C content (\%, m/m) & 85.55 & 32.35 & 82.42 & - & GB/T 19143-2003 \({}^{\mathrm{a}}\) \\ H content (\%, m/m) & 13.49 & 8.36 & 13.23 & - & GB/T 19143-2003 \({}^{\mathrm{a}}\) \\ O content (\%, m/m) & 0.66 & 58.06 & 3.99 & - & GB/T 19143-2003 \({}^{\mathrm{a}}\) \\ Heat Value (MJ\(\cdot\)kg\({}^{-1}\)) & 47.25 & 17.15 & 45.91 & - & ASTMD240 \\ Density (kg\(\cdot\)m\({}^{-3}\), 20 \({}^{\circ}\)C) & 737.80 & 862.60 & 778.16 & 850 & ASTM D4052 \\ Kinematic viscosity (40 \({}^{\circ}\)C, mm\({}^{\mathrm{a}}\)\(\cdot\)s\({}^{-1}\)) & 2.71 & 2.10 & 3.09 & 110.6 & ASTM D445 \\ Solidifying point (\({}^{\circ}\)C) & \(-15\) & \(<\)\(-58\) & \(-14\) & - & ASTM D5853 \\ Surface density (mN\(\cdot\)m\({}^{-1}\), 20 \({}^{\circ}\)C) & 31.1 & 37.6 & 33.7 & - & ASTM D1417 \\ Acid number (mg\(\cdot\)KOH\(\cdot\)g\({}^{-1}\)) & 0.12 & 33.10 & 0.82 & 0.035 & ASTM D664 \\ Water content(\%, \(\
u\)/\(\
u\)) & Trace & 24.50 & 1.35 & Trace & ASTM D6304 \\ \hline \end{tabular} \({}^{\mathrm{a}}\) China National Measurement Standard.  
\end{table} 
Table 2: The physical and chemical properties of oil samples. was obtained using a tension and compression sensor. The friction force was calculated by using the following formula [20]:  
\[\text{F}=20\,\times\,\text{U} \tag{1}\]  
\[\text{M}=\text{F}/\text{L} \tag{2}\]  
\[\Delta\text{m}=\text{m}_{1}\,-\,\text{m}_{0} \tag{3}\]  
SEM/EDS (JEOL Model JSM-6490) was used to investigate the morphologies and elements of the wear zones of the cylinder liner after the tribological tests. A surface roughness measurement system (Taylor-Hobson-6) was used to measure the roughness of the wear scars on the surfaces of cylinder liners that were magnified 10,000 times. The length of each sample was 0.08 mm, and the evaluation length was five times longer than the length of the sample, which was measured by using a Gaussian filter and sensor at 10,000:10 mm. The surface roughness is expressed by the contour arithmetic mean deviation \(Ra\).