## 2 Materials and Methods
### Estimation for FO Consumption and CO\({}_{2}\) Emissions  
The experiment also investigated the engine to record the daily seawater temperature, power output, and fuel consumption. The CO\({}_{2}\) emission was calculated according to fuel consumption. The conversion of CO\({}_{2}\) emissions refers to the guidelines for national greenhouse gas inventory issued by the IPCC [20,21]. As shown below, CO\({}_{2}\) emissions from fuel combustion are in Equation (1). \[\text{CO}_{2}\;\text{Emissions}=\sum_{\text{all fuels}}\biggl{[}((\text{AC}_{\text{ Fuel}}\times\text{CF}_{\text{Fuel}}\times\text{CC}_{\text{Fuel}})\times 10^{-3}-\text{EC}_{\text{ Fuel}})\times\text{CO}_{\text{Fuel}}\times 44/12\biggr{]} \tag{1}\]  
where \(\text{AC}_{\text{Fuel}}\) indicates the daily fuel consumption as tons of the unit. As the below equation shows:  
\[\text{AC}_{\text{Fuel}}=\;\text{Volume}\;\times\text{Sg}\times 1.006 \tag{2}\]  
Density correction, which Sg indicates, corresponds to the recorded operational temperature on board. As the below equation shows. \[\text{Sg}=\text{Density}\times\{1-[(\text{T}\;^{\circ}\text{C}-15\;^{\circ} \text{C})\times 0.00065]\} \tag{3}\]  
The \(V\) is the fuel oil volume (m\({}^{3}\)) recorded on board. It expresses the specific gravity (mt/m\({}^{3}\)) corresponding to the recorded operational temperature on board, and the coefficient of 1.006 is the oil purifier [22]. The density indicates the mass per unit fuel volume at 15 \({}^{\circ}\)C (mt/m\({}^{3}\)). T \({}^{\circ}\)C is the meaning of the temperature of FO after heating, while 0.00065 is a coefficient [23]. The conversion factor CF\({}_{\text{Fuel}}\) is converted according to the typical calorific value in international energy statistics of the International Energy Agency (IEA). At the same time, CC\({}_{\text{Fuel}}\) means the carbon content in fuel and heavy oil is 21.1 [24,25], and the unit is kg C/GJ. Both HFO and VLSFO are residual fuel oils. According to the National GHG inventory guidelines issued by IPCC (2006) [20,21], a residual fuel oil's carbon dioxide emission factor (CO\({}_{2}\) emission factors) is 77,400 kg/TJ. They are consistent with the same carbon content. The EC\({}_{\text{Fuel}}\) carbon in feedstocks and non-energy use should be excluded from fuel combustion emission; it is zero in the study scenario. The COF\({}_{\text{Fuel}}\) means the carbon oxidation factor [26,27], which refers to the proportion of carbon that is oxidized. This value is 1, indicating complete oxidation, and 44/12 is a ratio of the molecular weight ratio of CO\({}_{2}\) and C.  
Furthermore, the CO\({}_{2}\) emission indicates a calculation of the fuel consumption, also known as mass at kilograms (kg). The volume is a flowmeter to gauge the FO at m\({}^{3}\). The flowmeter measuring equipment utilizes the VAT, which is a professional instrument from France. The accuracy is at 0.1% deviation. Figure S1 provides the flowchart illustration and \begin{table}
\begin{tabular}{l l l} \hline \hline
**Item** & **Description** & **Unit** \\ \hline Launched date & 2013 & - \\ Length & 334.8 & Meter \\ Breadth & 45.8 & Meter \\ Draft design & 13.5 & Meter \\ Capacity & 8000 above & TEU \\  & MAN B\&W 9K98 ME Mark 7.1 & \\ Main engine & MCR: 56–80\% (77–88 RPM) & - \\  & NCR: 50,463 kW and shaft speed 93.7 RPM & \\ Gross tonnage & 99,998 & Tonnage \\ Service speed & 24.5 & knot \\ \hline \hline \end{tabular} Note: MCR—maximum continuous rating and NCR—normal continuous rating.  
\end{table} 
Table 2: Technical specifications of the container ships. Figure S2 exhibits an example gauge. The purifier is used by centrifugal force to separate the oil, moisture, and impurities with different specific gravity to obtain a proper FO. Before the FO is delivered to the purifier, the oil quality appears poor, with impurities that cannot be injected into the internal engine. After passing through the purifier, the FO quality's appearance tends to be a helpful oil, due to the high-speed rotation of the bowl disc [28].