# Tribological Behavior of Biomass Fast Pyrolysis Fuel and Diesel Blends
## 3 Results and Discussion
### Tribological Properties
#### 3.3.2 Wear Mechanism  
Figure 5 shows SEM images of the cylinder liner surface lubricated by emulsified biomass fuel with different ratios under the working condition of load 210 N and reciprocating frequency 5 Hz. It can be seen that the longitudinal oblique scratches are caused by a machining-honing process. With the increase in biomass fuel content in emulsified biomass fuel, more and more furrows (transverse) and corrosion pits appear on the cylinder liner surface, which may be due to the corrosion of metal caused by acidic substances produced by emulsified biomass fuel during friction. As a result, there are many irregular corrosion pits, and some corrosion products are scattered into the fuel during the reciprocating movement, which promotes the formation of more corrosion pits. With the increase in biomass fuel content in emulsified biomass fuel, the acid substances and oxygen content in the fuel increase, accelerating the corrosion of the base material, reducing the surface strength of the base material and loosening the texture. It is easy for the material to fall off and generate wear debris in the reciprocating process, and some wear debris accelerate the formation of furrows in the cylinder liner surface during the reciprocating process of the piston ring. Figure 4: Soaking results of emulsified biomass fuel oil with different proportions. As is well known, the chemical compositions of biofuel influenced the tribological behavior of diesel fuel. However, different preparation processes of biomass will cause varied chemical compositions of biofuel. The thermal decomposition of wheat straw at 350 \({}^{\circ}\)C and 450 \({}^{\circ}\)C was studied using the Py-GC/MS technique in a helium atmosphere to determine the gaseous compounds formed during biomass gasification under anaerobic conditions. The results obtained indicated the formation of compounds classified as phenols (vanillin, hydroxymethylfurfurral) [21], which were similar with our previous results about biomass fast pyrolysis fuel [22]. In order to further explore the corrosion and wear characteristics of emulsified biomass fuel with different ratios under the above working conditions, EDS analysis related with the chemical composition of fuel was carried out on the wear mark surface of the cylinder liner, and the analysis results are shown in Table 3.  
Table 3 shows the EDS analysis results of the cylinder liner surface lubricated by emulsified biomass fuel with different ratios. It can be seen that with the increase in biomass fuel content, the content of element C on the cylinder liner surface also increases. This is because the long carbon chain components and some C-containing organics in emulsified biomass fuel increase with the increase in biomass fuel content. These substances are adsorbed during friction and deposited on the friction surface through tribo-chemical reaction, which leads to an increase in the content of element C on the cylinder liner surface. Figure 5: SEM images of the surface of the lower cylinder liner lubricated by the emulsified biomass fuel with different ratios. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{_Varied Blends_} & \multicolumn{8}{c}{_Element (wt.\%)_} \\ \cline{2-9}  & **C** & **O** & **Fe** & **Mn** & **Cr** & **Si** & **P** & **S** \\ \hline
5 wt.\% & 1.86 & 6.39 & 86.07 & 1.06 & 0.36 & 3.43 & 0.81 & \\
10 wt.\% & 2.99 & 16.08 & 70.98 & 1.26 & 0.50 & 6.77 & 1.43 & \\
20 wt.\% & 7.25 & 24.78 & 55.26 & 1.07 & 0.43 & 9.98 & 0.67 & 0.56 \\ \hline \hline \end{tabular} Experimental conditions: load—210 N; frequency\(-\)5 Hz; time—6 h; and oil supply—dripping lubrication.  
\end{table} 
Table 3: EDS analysis results of the lower cylinder liner surface lubricated by emulsified biomass fuel with different proportions. The content of the O element on the cylinder liner surface increases with the increase in biomass fuel content, but the content of the Fe element decreases. This may be because the existence of the oxygen element promotes the generation of corrosion wear.