3.2.3. LCA Modelling

While GaBi software was employed for LCA, Figure 7 illustrates the WtT LNG supply model with LNG flow equivalent to the life cycle models of LNG in Figure 3. LNG of 2.04 <sup>×</sup> <sup>10</sup><sup>5</sup> kg provides an LHV of 1.0 <sup>×</sup> <sup>10</sup><sup>7</sup> MJ, a functional unit for analysis. After the purification and liquefaction process, 2.27 <sup>×</sup> <sup>10</sup><sup>5</sup> kg of natural gas is converted into LNG.

The LCA model for MGO supply pathway is presented in Figure 8 which is consistent with the life cycle of oil-based marine fuel as presented in Figure 3. To deliver 1.0 <sup>×</sup> 107 MJ of MGO in final combustion, 5.52 <sup>×</sup> <sup>10</sup><sup>5</sup> kg of crude oil is required. Crude oil is converted to MGO in refineries in South Korea. After the process, 2.34 <sup>×</sup> 10<sup>5</sup> kg of MGO is produced, which gives an LHV of 1.0 <sup>×</sup> 10<sup>7</sup> MJ as defined by the functional unit.

Figure 9 presents TtW models for both LNG and MGO. This range was limited to onboard fuel consumption. Emissions were calculated based on fuel consumption: 2.04 <sup>×</sup> 105 kg LNG fuel and 2.34 <sup>×</sup> <sup>10</sup><sup>5</sup> kg MGO, giving the same 1.0 <sup>×</sup> 107 MJ of LHV during combustion.

The LCA model for WtW of LNG and MGO fuels incorporates the Well to Tank and Tank to Wake models as shown in Figure 10.

**Figure 9.** TtW LCA model for LNG and MGO fuel.

*J. Mar. Sci. Eng.* **2019**, *7*, 359

**Figure 10.** WtW LCA model for LNG fuel and MGO fuel.
