Assessment of technical and environmental performance of Marine Alternative fuels for Container Ships

11 Environmental issues, for example, the expanded air pollutant emissions from ships are progressively affecting the 12 operation of ships. Therefore, International Maritime Organization (IMO) has adopted many goals to decarbonizing the 13 shipping industry by at least 40% by 2030. Marine fuels play a major role in these goals because of the emissions resulting 14 from the combustion process. Therefore, the present research proposes to convert the conventional engine operated by 15 marine diesel oil (MDO) to a dual-fuel engine operated by either natural gas (NG) or methanol. As a case study, A15- 16 class container ship is investigated. The results showed that the dual-fuel engine operated with (98.5% NG and 1.5% 17 MDO) will reduce CO 2 , SOx, and NOx emissions by 28%, 98% and 85%, respectively when compared with their values 18 for conventional diesel engine. On the other hand, the reduction percentages reach to 7%, 95% and 80% when using a 19 dual-fuel engine operated with (95% Methanol and 5% MDO), respectively. The proposed dual-fuel engines operated by 20 either NG and methanol will improve the ship energy efficiency index by 26% and 7%, respectively.


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Currently, there are several legislations in addition to many goals adopted by the International Maritime Organization 24 (IMO) to reduce greenhouse gases (GHG) and achieve a blue economy (Psaraftis and Kontovas 2021). One of those goals 25 is to reach a 50 percent reduction in the percentage of GHG emitted from ships by 2050 compared to 2008 (Joung et al. 26 2020). There are several mechanisms that can be followed to reduce GHG from ships, include ship design, propulsion 27 systems, alternative fuels (Welaya et  and renewable energy (Sadek and Elgohary 2020). Among these methods, alternative fuels of less carbon content are 29 considered one of the best ways to reduce the GHG emitted from ships. The main alternative marine fuel types may be 30 found in two forms: liquid and gaseous fuels. Liquid marine alternative fuels include Methanol, Ethanol, and Bio liquid 31 fuel. On the other hand, the main alternative gasses fuels include Natural gas, Propane, Hydrogen, and Ammonia (Elkafas 32 et al. 2021b). 33 Two alternative types will be considered throughout the present project, mainly: Natural gas (NG) and Methanol. 34 Selection of the previous types is the matter of searching for alternative fuels that have less emissions to be applied on The primary segment of natural gas is methane (CH4), this fuel is the least carbon and sulfur content and consequently 41 with the most promising option to decrease carbon dioxide (CO2) and Sulfur dioxide (SOx) emissions (Elgohary et al. 42 2015). Besides, the burning of natural gas in comparison with diesel is characteristically cleaner regarding Nitrogen oxide 43 (NOx). Moreover, natural gas appears as a financially motivating measure for vessel types spending a long period of their 44 cruising time like handy size tankers, RO-RO vessels, and container ships (Elkafas et al. 2021a). 45 All the previous studies, whether research projects or research papers that dealt with the importance of alternative 46 fuels usage onboard ships, confirm that the maritime industry has not benefited the most from alternative fuels. Moreover, 47 it confirms the necessity of conducting many other studies to determine the potential benefits from alternative fuel onboard 48 ships from technical and environmental point of view. 49 The present research aims at assessing the environmental and technical performance of the proposed alternative fuels 50 (natural gas and methanol). As a case study, A15-class container ship is investigated. The assessment is based on a 51 comparative study between alternative fuels and conventional diesel fuel from environmental and energy efficiency point 52 of view. 53 The individual emission energy-based rate in differs from type to another. In case of CO2 emission, it is based on the 63 conversion factor between fuel and CO2 which depend on the carbon content in fuel, therefore, its value differs from fuel 64 to another. The energy-based rate of CO2 emission ( /01 ) measured in g CO2/kWh can be calculated using Eq.

Environmental and technical assessment method
(2) based on Regarding the air pollution emission inventory recommendation from IMO, NOx emission factor expressed in g/kWh 69 for slow speed diesel engine depends on the ship construction date (Elkafas et al. 2021a). The first level of control (Tier 70 I) applies for ships constructed on 1 January 2000 or after and can be calculated as shown in Eq. (3) which depends on 71 the engine's rated speed (n). 72 506 = 45 × :;.1 (3) A slow speed diesel engine (SSDE) that is installed on a ship constructed on 1 January 2011 or after (Tier II), a 73 reduction equal to 15% should be fulfilled compared with Tier I NOx emission value (Ammar and Seddiek 2020). On the 74 other hand, NOx emission factor for natural gas engine and methanol engine is 2.16 g/kWh and 2.47 g/kWh, respectively 75 It is seen that lower the sulfur content in fuel is led to reducing the specific emission rate of SOx, which is the reason 79 why more and more strict demands towards lower sulfur content in marine fuel. Islands. Table 2 shows the technical data of the ship (Hapag-LIoyd 2021). 105 The ship is currently powered by a two SSDE (MAN 9S90 ME-C) with an output of 37,620 kW at 72 rpm which 110 operated with marine diesel oil (0.5% S). The main engine is proposed to be converted to 9G80ME-C10.5-GI dual-fuel 111 engine (DFE) with the same power and speed operated by natural gas and 1.5% MDO as a pilot fuel. On the other hand, 112 it is proposed to be converted to MAN B&W ME-LGI dual-fuel engine that can run on methanol and 5% MDO as a pilot 113 fuel. The proposed engine's cylinder head is equipped with two valves for gas injection and two conventional valves for 114 the pilot fuel oil. ME-GI has the same efficeincy, power and dimensions of ME-C. Based on Hapag-Lloyd reports, around 115 350 container sites will be lost for the additional gas storage system (Peter Pospiech 2019). 116

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The environmental performance can be assessed by evaluating the exhaust emission rates per trip. The examined emission 118 types are CO2, SOx, and NOx, as these types are related with IMO regulations. The assessment process depends on the 119 comparative study between the proposed dual-fuel engine operated with natural gas or methanol and the conventional 120 SSDE operated with MDO (0.5%S). The first step in evaluating the environmental benefits of proposed dual-fuel engine 121 is to calculate the energy-based emissions factors as discussed before. The different emissions rates per trip can be 122 calculated based on the specified trip from Busan to Hamburg. The relative emissions rates of the proposed dual-fuel 123 engine compared to diesel engine are shown in Fig.1.  124 125 Fig. 1 Relative emissions rates of the proposed dual-fuel engine compared to diesel engine 126 For the current case study, the emissions rates of SSDE are 39.1 ton/hr, 2.13 kg/min and 20.4 kg/min for CO2, SOx, 127 and NOx, respectively. These rates are reduced after applying dual-fuel engine (98.5% NG and 1.5% MDO) to 28.2 128 ton/hr, 0.032 kg/min and 2.97 kg/min with reduction percentages of 28%, 98% and 85%, respectively. These rates are 129 reduced after applying dual-fuel engine (95% Methanol and 5% MDO) to 36.25 ton/hr, 0.107 kg/min and 0.032 kg/min 130 with reduction percentages of 7%, 95% and 80%, respectively. 131 NOx and SOx emission rates should be compared with the IMO 2016 and 2020 emission-limit rates, respectively 132 (Elkafas et al. 2021a, b). IMO 2020 SOx emission limit rate can be predicted based on fuel sulfur content (0.5%) which 133 equals 2.133 kg/min. For the case study, SOx emission rates can be calculated for different pilot fuel percentage in dual-134 fuel engine to assess the effect of its value on emission rates as shown in Fig.2.  135 136 Fig. 2 SOx emission rates at different pilot fuel percentages 137 It can be noticed that SOx emissions rates for dual-fuel engine are compliant with IMO 2020 limit at different pilot 138 fuel percentage. 139 IMO 2016 NOx emission limit rate can be predicted based on engine speed which equals 4.26 kg/min. For the dual-140 fuel engine operated by natural gas and pilot fuel, NOx emissions rates can be calculated for different pilot fuel 141 percentages to evaluate the impact of its value on emission rates as shown in Fig.3 As shown in Fig.3, the dual-fuel engine operated by natural gas and methanol will be compliant with the required 145 IMO limit if the percentage of pilot fuel is lower than 8.8% and 6.4%, respectively. 146 Furthermore, the energy efficiency can be assessed by the calculation of EEDI for the proposed dual-fuel engine as 147 recommended by IMO. By conducting the reference EEDI procedure to the case study, it is shown that the reference 148 EEDI and its value in the three phases can be calculated based on the deadweight of the container ship as investigated in 149 This reference value will be compared with the actual attained EEDI for the case study powered by SSDE which can 153 be calculated by using Eq. (7) based on 24 knots service speed, 3.206 ton-CO2/ton-fuel conversion factor of fuel to CO2. 154 The attained EEDI will be 11.91 g CO2/DWT-NM. It is noticed that the current EEDI of SSDE is fulfilling the EEDI 155 requirement until phase 2 but must be reduced to comply with EEDI phase 3. 156 To evaluate the energy efficiency benefits for the selected dual-fuel engine operated by either natural gas or methanol, 157 attained EEDI should be calculated. Based on Eq. (7) and Eq. (8), the attained EEDI for dual-fuel engine (98.5% NG and 158 1.5% MDO) and (95% Methanol and 5% MDO) is 8.77 gCO2/DWT-NM and 11.07 g CO2/DWT-NM, respectively. To 159 assess the results, it should be compared with the reference EEDI at different phases as shown in Fig.5 It is shown that, the proposed dual-fuel engine operated by (98.5% NG and 1.5% MDO) will comply with the required 163 IMO phases now and in the future as the attained EEDI is about 61%, 69% and 79% of the reference EEDI at phase 1, 164 phase 2 and phase 3, respectively. On the other hand, the proposed dual-fuel engine operated by (95% Methanol and 5% 165 MDO) will comply with IMO phase 1 and phase 2 as it is about 77% and 87% of the reference EEDI value, respectively. 166 While it will comply with the required IMO phase 3 by a small percentage, as the attained EEDI will reach 99.5% of the 167 required EEDI. 168

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The application of dual-fuel engine operated by natural gas or methanol on A15-class container ship has been investigated 170 from environmental and energy efficiency point of view. The main conclusions from the current study are: 171

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• From environmental point of view, using dual-fuel engine operated with 98.5% NG and 1.5% MDO will comply 173 with the required IMO emissions regulations. This will lead to reductions in CO2, SOx, and NOx emissions by 28%, 174 98% and 85%, respectively when compared with their values for SSDE operated by MDO (0.5%S). While the another 175 proposed dual-fuel engine operated by 95% Methanol and 5% MDO will lead to reductions by 7%, 95% and 80%, 176 respectively. Furthermore, the dual-fuel engine operated by natural gas and methanol will be compliant with the 177 required IMO limit if the percentage of pilot fuel is lower than 8.8% and 6.4%, respectively. 178 • From energy efficiency point of view, the dual-fuel engine operated by (98.5% NG and 1.5% MDO) will comply 179 with the required IMO EEDI phases now and in the future. On the other hand, the dual-fuel engine operated by (95% 180 Methanol and 5% MDO) will comply with IMO EEDI phase 1, phase 2, and phase 3 by about 77%, 87%, and 99. Reference EEDI