## 3 Results and Discussion
### Wear Mechanism Analysis  
The wear mechanism of the biomass fast pyrolysis fuel on the piston ring and cylinder liner was investigated via composition analysis and varying the kinematic viscosity of the oil samples. Figure 8 shows FT-IR spectra of EBF and FFEO, in which EBF shows more active function groups from 5 wt% crude biomass oil compared with FFEO. The broad peak range at 3000 to 3600 cm\({}^{-1}\) was attributed to the free hydroxyl (-OH) in the crude biomass oil. Peaks at 1751 and 1615 cm\({}^{-1}\) were detected in two oil samples, which indicated the existence of acids, ethers, and esters. The main functional groups shown in Figure 8 are the same as those found in other literature [27], even though these biomass oils could have been produced from different raw materials or processes; their compositions were also very complex and variable. These active function groups would influence the wear mechanism, because they would react with the FFEO additives to decrease the oil film thickness during the rubbing process. The thinner oil film resulted in serious wear that could explain the  
Figure 7: EDS analysis of cylinder liner wear zones with 20 and 80 vol% EBF in FFEO: (**a**) 20 vol% EBF, (**b**) 80 vol% EBF.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{8}{c}{**Element Content (wt%)**} \\ \cline{2-10}  & **C** & **O** & **Fe** & **Zn** & **Cr** & **Mg** & **Si** & **Ca** \\ \hline Lubri a & 0.91 & - & 95.88 & 0.22 & 1.15 & 0.81 & 0.77 & 0.26 \\ Lubri b & 22.74 & 31.86 & 43.12 & - & - & - & 2.29 & - \\ \hline \hline \end{tabular}  
* a 20 vol% EBF; b 80 vol% EBF.  
\end{table}
Table 3: EDS analysis of the cylinder liner wear zones lubricated with 20 vol% and 80 vol% EBF in FFEO.  
decrease in the surface roughness when the EBF content was as much as 60 vol%. The oil film thickness was also attributed to the variations in kinematic viscosity.  
Figure 9 illustrates the variations in kinematic viscosity of the oil samples as a function of temperature. The viscosity decreased as temperature and/or EBF content in FFEO increased. The effects of corrosive wear also had a key function in promoting wear during the rubbing process. This observation is illustrated in Figures 4c and 5g.  
The surface asperities were easily polished, which resulted in low surface roughness, high friction coefficient, and increased mass loss when EBF was added to FFEO. The simple schematics in Figure 10 explain the effect of EBF on the tribo  
Figure 8: FT-IR analysis of biomass crude oil and emulsified biomass fuel: (a) biomass crude oil, (b) emulsified biomass fuel.  
Figure 9: Variations in kinematical viscosity of oil samples as functions of temperature.  
The surface asperities of the cylinder liner and piston ring were protected by the lubrication oil film through the FFEO. As shown in Figure 10, the polishing of surface asperities and decrease in oil film thickness when the EBF was added to the FFEO subsequently decreased the surface roughness of the cylinder liner during the rubbing process. The increase in surface roughness upon addition of as much as 80 vol% EBF was attributed to the corrosion function of EBF.  
The active components of pure EBF were easily absorbed on the frictional pair to form a tribochemical film, which could explain the low friction coefficient and mass losses of the cylinder liner and piston ring, especially for the tribo-condition in the state of boundary lubrication. These findings will be helpful to understanding the tribochemical roles of compositions that include EBF together with the engine lubricating additives and basestocks.