# Performance Assessment and Scooter Verification of Nano-Alumina Engine Oil
## 4 Results and Discussion  
From Figure 5a, the higher the density of the test sample at the higher weight fraction was due to the higher density of the nanoparticles themselves. With higher test sample temperatures, the density dropped because of increased volume expansion. From Figure 5b, with more nanoparticles added, the viscosity was higher due to the interfacial relationship between the solid particles and the liquid molecules. In Figure 5c, the lower specific heat of the test sample at the higher weight fraction was due to the lower specific heat of the nanoparticles themselves. Figure 4: Demanded speed and tracking speed of the ECE40 driving cycle. Figure 3: Dynamometer test for a scooter with a 125 c.c. engine. The influence of specific heat and density of the NAEO at various weight fractions was not significant, because the added weight fraction was low based on the concept of a solid-liquid mixture. Therefore, the effect of the specific heat and density of the NAEO on the wear performance and loading of the mechanical parts should be relatively small. However, the viscosity of the 2.5 wt. % NAEO was  
Figure 5: Basic properties of engine oil (EO) and nano-alumina engine oil (NAEO): (**a**) density; (**b**) viscosity; and (**c**) specific heat. significantly higher than the EO. It is noteworthy that the higher weight-fraction Al\({}_{2}\)O\({}_{3}\)-NAEO with higher viscosity did not flow easily; therefore, the highly-viscous NAEO was difficult to clean from the surface of the disk. Consequently, the inability to remove debris from the disk surface may cause an increase in interface roughness between the fixed and movable elements, causing an increase in wear weight loss. However, the shear thinning behavior of the NAEO at high rotating speeds may partly solve the problems described above [9; 19; 22]. Therefore, the search for the optimal weight fraction of NAEO must include a wear test to confirm the optimal performance of the specific weight fraction. Figure 6 displays the wear loss of the NEAO with various weight fractions and normal forces at constant rotating speeds of 500 and 1000 rpm. For the weight fractions, it shows that the 1.5 wt. % has better anti-wear performance. This is because at lower weight-fraction NAEO (<1.5 wt. %), the amount of nanoparticles decreases so that the protection and anti-wear effects decrease, causing the wear loss to increase. With a higher weight-fraction NAEO (>1.5 wt. %), though the amount of nanoparticles increases, debris will be trapped near the surface and cannot be released because the higher weight-fraction NEAO has higher viscosity. Therefore, the wear loss also increases. Overall, higher rotational speeds will indeed result in higher wear loss. Figure 6: Wear loss with various weight fractions and normal forces at (**a**) 500 rpm and (**b**) 1000 rpm. Figure 7 illustrates the wear loss at four weight fractions of the Al\({}_{2}\)O\({}_{3}\) nanoparticles at various rotating speeds with a constant normal force of 350 N. For the weight fractions, it shows that the 1.5 wt. % has better anti-wear performance, because in a lower weight-fraction NAEO (<1.5 wt. %), the amount of nanoparticles decreases so that the protection and anti-wear effects decrease, causing the friction to increase. With a higher weight-fraction NAEO (>1.5 wt. %), though the amount of nanoparticles increases, the debris will be trapped near the surface and cannot be released. Therefore, the wear loss also increases. Overall, higher normal force will indeed result in higher wear loss. Since 1.5 wt. % NAEO had the best anti-wear performance (see Figures 6 and 7), the wear loss of 0 wt. %, 1.5 wt. %, and 2.5 wt. % NAEO at various rotating speeds and normal forces is shown in Figure 8. Figure 8 shows that with higher speed (at the same normal force on the disk), the wear effect is more obvious. Similarly, at higher normal force and with the same rotating speed of the disk, the wear increases.