## 3 Results and Discussion
### Four-Ball Antiwear Test  
The antiwear test of the lubricants was performed to investigate the wear-resisting properties of the lubricants according to the ASTM 4172 standard. The tests were carried out as per the standards at a specific temperature (75 degrees Celsius) and a specific load (392 N). The length of the wear scars of all three bottom balls was measured and the average of these wear scars was recorded. The frictional force was recorded and analyzed to find any sharp peaks during the test duration. The test was selected as a primary evaluation of the antiwear properties of the lubricant in sliding contact. Figure 9 presents examples of wear scar photos. The wear scar diameters of the bottom steel balls were analyzed and the images were captured with a digital camera installed on the optical microscope. Some of the examples are presented in Figure 9. The wear scar diameters were measured using an image acquisition system and their size was determined as the average value of the horizontal and vertical measurements. Then, this value was used for the calculation of the wear scar diameter presented in Table 3.  
Figure 8: Examples of friction torque course variability for lubricating oil samples that have worked for different times and are diluted by fuel to a different extent. Red points—estimated load seizure limit (\(F_{\alpha z}\)) for each oil sample. Point 1—estimated load seizure limit (\(F_{\alpha z}\)) for **fresh oil**. Point 2— example of estimated load seizure index (\(F_{t}\)) for **fresh oil**. Load points marked for each sample estimated load seizure limit. Figure 9: Examples of wear scar pictures captured under microscope observation and measurement for different engine running hours from fresh oil to 32 running hours respectively. (**a**) fresh oil, (**b**) after 1 h, (**c**) after 2 h, (**d**) after 4 h, (**e**) after 6 h, (**f**) after 8 h, (**g**) after 10 h, (**h**) after 12 h, (**i**) after 15 h, (**j**) after 18 h, (**k**) after 24 h, (**l**) after 32 h.  
Seizure resistance was determined based on the LSI (\(F_{t}\)) and the LSL (\(F_{oz}\)), which correspond to the nominal pressure on the surface of the wear mark at the node seizure as limit seizure pressure (\(p_{oz}\)) and is calculated from Formula (3):  
\[p_{oz}=0.52\frac{F_{oz}}{d^{2}}\quad[\mathrm{N/mm^{2}}] \tag{3}\]  
where:  
\(d\)--average diameter of the wear scar on the balls [mm];  
0.52--coefficient resulting from the distribution of forces in the four-ball friction node;  
\(F_{oz}\)--load seizure limit for each sample. Table 3 depicts calculation results for the average values of parameters measured during the tests. The trace diameters represent the average wear scar size measured under a microscope in two directions (length and width). Similarly, the load seizure index and load seizure limit in Table 3 are the average values from various measurements for each oil working time. The limit seizure pressure \(p_{oz}\) is the value calculated with Equation (3) from the average trace diameter and average load seizure limit. The load seizure limit values recorded by the tribometer for each oil sample are shown in Figure 10. This graph shows that for all seizure samples presented, the LSL limit was reached at a similar load level, as shown by the trend line for these values (black line). This can be understood as follows: the amount of fuel diluted in oil has no effect on LSL, despite increasingly larger, visible deviations from the values designated as the trend line. \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Oil Working** & **Trace** & \begin{tabular}{c} **Load** \\ **Seizure Index** \\ **\(F_{t}\)** \\ \end{tabular}  & \ \begin{tabular}{c} **Load** \\ **Seizure Limit** \\ **\(F_{oz}\)** \\ \end{tabular}  & \begin{tabular}{c} **Limit** \\ **Seizure Pressure** \\ \(P_{oz}\) \\ \end{tabular}