## 3 Results and Discussion
### Fuel Consumptions and CO\({}_{2}\) Emissions for Both Fuel Options  
The 8000 TEU container ships' travelled on round trips back and forth between Asia and C.A. As Table 3 indicates, the specific gravity of the fuel is at 0.940 mt/m\({}^{3}\) and 0.933 mt/m\({}^{3}\) for HFOWD and VLSFO, respectively (\(p\) = 0.000). The lower heating value is 10,210 kcal/kg and 10,294 kcal/kg, respectively (\(p\) = 0.000). The specific gravity of fuel (\(p\) = 0.000), the heating value (\(p\) = 0.000), daily fuel consumption (\(p\) = 0.031), and the daily CO\({}_{2}\) emission (\(p\) = 0.014) of the main engine in the HFOWD and VLSFO from C.A. to Asia are statistically significant. Figure 2a indicates that the main engine fuel consumption from Asia to C.A. is 131.63 tons/day and 142.32 tons/day for HFOWD and VLSFO, respectively. Thus, there is a difference of 10.69 tons/day (7.8%). It turns out that HFOWD saves more fuel oil than VLSFO. Similarly, the main engine fuel consumption from C.A. to Asia is 128.05 tons/day and 140.09 tons/day for HFOWD and VLSFO, respectively, meaning there is a difference of 12.04 tons/day (9%). The HFOWD can save 11.36 tons/day (8.4%) of fuel compared with the VLSFO. Figure 2b illustrates that the CO\({}_{2}\) emission from Asia to C.A. is 435.18 tons/day and 474.8 tons/day for HFOWD and VLSFO, respectively. As a result, the HFOWD can save 39.62 tons/day of CO\({}_{2}\) emissions. Similarly, the CO\({}_{2}\) emissions from C.A. to Asia are 421.98 tons/day and 467.02 tons/day for HFOWD and VLSFO, respectively. The HFOWD can save 45.04 tons/day of CO\({}_{2}\) emissions. On average, it turns out that HFOWD can save 42.33 tons/day (9.5%) of CO\({}_{2}\) emission in comparison with the VLSFO. Under the same main engine output, 0.5% VLSFO consumes more fuel and produces more CO\({}_{2}\) emissions per metric ton than HFOWD. According to Alphhainer's statistics in July 2021, 85.2% of the world's approximately 5447 container ships used VLSFO, and 785 (14.4%) adopted HFOWD equipped with desulfurization towers, of which 7500-9999 TEU container ships account for the most significant proportion (there are 129 (16.4%)) [19]. According to the statistic usage of container ship fuel in 2021 and the above findings, the CO\({}_{2}\) emissions of container ships after IMO's 2020 sulfur cap are higher than before. Just as the results of Kontovas (2020) demonstrate [18], the total CO\({}_{2}\) emissions of marine fuel oil in 2020 will be 638.32 million tons, higher than the total CO\({}_{2}\) emissions of heavy fuel oil in 2019 of 618.6 million tons [18]. The results of this study are consistent with the conclusions of [PERSON] et al. (2021) [10]. VLSFO creates more CO\({}_{2}\) emissions than HFOWD. There are two reasons why the main engine's daily fuel consumption of VLSFO is higher than the HFOWD. At first,  
Figure 2: Compare the HFOWD (in blue) and VLSFO (in orange) from Asia to C.A, back and forth: (**a**) fuel consumption of the VLSFO is significantly higher than the HFOWD; (**b**) CO\({}_{2}\) emissions of the VLSFO are significantly higher than the HFOWD. the supplier mixed the instability, poor lubricity, and poor compatibility of the impurities oil with the VLSFO. They are mainly composed of residuals and distillate components. As a result, the blended fuel reduces its inherent stability and compatibility. It causes waxy components, asphaltene precipitation, decreased viscosity, poor ignition, and fine catalyst content. Furthermore, high levels of catalyst fine content may cause abrasive wear to engine components [29]. Secondly, in investigating ways to meet IMO's requirements for sulfur restriction, much evidence has emerged indicating that the VLSFO also damages the engine. Adding lubricants and chemical additives can reduce the damage of VLSFO to the engine [30]. Therefore, the VLSFO may lead to the main engine wear [10], causing high fuel consumption and CO\({}_{2}\) emissions. In addition, the engine is still designed for high-sulfur equipment [10]; it's design does not account for low-sulfur oil.