# Performance Assessment and Scooter Verification of Nano-Alumina Engine Oil
## 4 Results and Discussion
This is because with either higher normal force or rotating speed, the amount of debris from the disk surface caused an increase in interface roughness between the pin and disk; thereby, it caused an increase in wear loss. Experimental results displayed in Figure 8 further confirm that the 1.5 wt. % NAEO had the best anti-wear performance. Figure 7: Wear loss with various weight fractions and rotating speeds at (**a**) 350 N and (**b**) 450 N normal forces. Figure 8: The wear loss of (**a**) 0 wt. %; (**b**) 1.5 wt. %; and (**c**) 2.5 wt. % nano-alumina (Al2O3) engine oil (NAEO) at various rotating speeds and normal forces. Regarding the anti-wear performance of test samples from Figures 6-8, the wear loss of the disk was lower for the 1.5 wt. % NAEO than for the EO. However, the NAEO with a higher weight fraction of Al\({}_{2}\)O\({}_{3}\) did not guarantee a more favorable anti-wear performance. This phenomenon primarily occurred because the higher weight fraction NAEO with higher viscosity flows more uneasily. 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 caused an increase in interface roughness between the pin and disk. This then caused an increase in wear loss. However, the nano-oils may reduce wear loss by the the rolling-sliding effect, by providing a protective film, by third-body effect, by the mending and smoothing effect of surface roughness, by shear thinning, and by the high thermal conductivity of nano-oils. The effects mentioned above can reduce the wear loss of test samples. These effects, combined with the effect of viscosity, thereby determine the optimal nanoparticle weight fraction in nano-oils. Therefore, the optimal tribological performance was observed in the NAEO with 1.5 wt. % Al\({}_{2}\)O\({}_{3}\) nanoparticles; moreover, the wear loss of the 1.5 wt. % Al\({}_{2}\)O\({}_{3}\)-NAEO was lower than that of the EO. Therefore, the 1.5 wt. % NAEO and EO were selected as the test samples for the dynamometer test. For the real scooter test on the dynamometer, each experimental item was tested three times for the average value. The experimental results of fuel consumption are shown in Figure 9. For the constant speed test (50 km/h), the fuel consumption of the EO was 58.10 km/L, while the fuel consumption of the NAEO was 59.35 km/L. This shows that the improvement in fuel consumption comparing the NAEO to EO is 2.15%. For the ECE40 driving cycle, the fuel consumption of the EO was 38.35 km/L, while the fuel consumption of the NAEO was 37.23 km/L. The improvement of fuel consumption comparing the NAEO to the original engine oil is 3.01%. The average fuel consumption is defined as:  
\[FC_{avg}=1/(0.6/FC_{ECE}+0.4/FC_{const}) \tag{1}\]  
where \(FC_{avg}\), \(FC_{ECE}\), and \(FC_{const}\) represent the average fuel consumption, fuel consumption of the ECE cycle, and the fuel consumption at constant speed, separately. The average fuel consumption for the EO is calculated to be 43.48 km/L, while it was 44.67 km/L for the NAEO case according to Equation (1). Therefore, the fuel consumption improvement for the NAEO was calculated to be 2.75%. Figure 10 illustrates the comparison of the original EO and NAEO at four constant throttle positions (20%, 40%, 60%, and 90%). Each experimental item was tested three times. For throttle position at 20%, the fuel consumption for EO was 54.35 km/L, while it was 55.62 km/L for the NAEO case. The improvement was 2.28%. For throttle position at 40%, the fuel consumption for EO was 56.20 km/L, while it was 58.95 km/L for the NAEO case. The improvement was 4.66%. For throttle position at 60%, the fuel consumption for EO was 54.32 km/L, while it was 56.95 km/L for the NAEO case. The improvement was 4.62%. For 90% throttle position, the fuel consumption for EO was 53.45 km/L, while it was 55.63 km/L for the NAEO case. The improvement was 3.92%. The average fuel improvement for the four throttle positions was 3.87% ((2.28 + 4.66 + 4.62 + 3.92)%/4).