## 3 Analysis of the Previous Prediction
### Propulsion Solutions on LNG Ships Comparison  
In an earlier analysis, three types of propulsion were examined: steam turbines, XDF, and MEGI. The choice of propulsion type for LNG vessels is critical as it affects capital and operating costs, emission levels, propulsion compartment size, vessel reliability, and compliance with key regulations [7; 26]. Steam turbines are widely used in the maritime industry due to their adaptability and ability to be installed in various systems and configurations. Steam propulsion systems are most commonly found in the engine rooms of LNG vessels and remain the predominant mode of propulsion for these vessels [32]. Nearly twenty years ago, steam turbine systems fueled by boil-off gas and HFO (heavy fuel oil) were the only propulsion option for LNG carriers [7]. \begin{table}
\begin{tabular}{c c c c} \hline
**Year** & **Predicted** & **Realized** & **Difference (\%)** \\ \hline
2020 & 584.0 & 572 & \(-\)2.05 \\
2021 & 650.0 & 607 & \(-\)6.61 \\
2022 & 706.0 & 641 & \(-\)9.20 \\
2023 & 755.0 & 668 & \(-\)11.52 \\
2024 & 803.0 & 701 & \(-\)12.70 \\ \hline \end{tabular}
\end{table} 
Table 4: LNG fleet size comparison with the previous research [7; 26; 30]. Figure 4: Number of LNG ships (fleet size) from 2010 to 2024 [7; 26; 30]. Today, steam turbines are generally considered an outdated technology for ship propulsion. However, one of the main advantages of steam propulsion systems over diesel engine systems is their higher reliability and lower probability of failure. These traditional systems generally require less maintenance and are known for their robustness. The advantages of internal control of such systems are their simplicity and affordability, and only a single dock visit is required to overhaul the turbine. Routine inspections are rarely required and are usually only carried out for obvious malfunctions [33]. It has already been mentioned that a steam turbine is primarily fueled with vaporized gas from cargo tanks or, if this is insufficient, with an alternative HFO. One of the main disadvantages of steam turbines is their low efficiency, which is only 35% at full load. The current fleet comprises 240 steam-turbine-powered ships, which corresponds to 34.2% of the total fleet [7]. However, new ships with steam turbines are no longer being built due to problems with rising fossil fuel prices and stricter emission regulations, indicating a shift to newer and more environmentally friendly technologies. These advanced technologies offer higher efficiency and greater operational flexibility as they allow for a wider range of operating speeds and adaptation to different operating conditions. Compared to steam turbine propulsion, modern propulsion systems such as Dual-Fuel Diesel Electric (DFDE) engines, Tri-Fuel Diesel Electric (TFDE) engines, low-pressure Winterthur Gas and Diesel (XDF) engines, and M-type electronically controlled gas injection (MEGI) engines offer 25-50% greater efficiency and cost effectiveness. The company Winterthur Gas and Diesel (WinGD) developed a low-pressure injection system with a high air-fuel ratio in the cylinder. It was based on a well-known [PERSON] slow-speed engine using Wartsila's dual-fuel technology, in which a lean air-gas mixture is burned in the Otto cycle and injected in the gas mode, while a small amount of diesel pilot fuel is injected into the cylinder for ignition at top dead center (TDC). The first XDF engine was delivered in 2017 [34]. The MEGI engine type stands for the M-type electronically controlled gas injection, developed by MAN B&W. This engine type is based on the fact that the fuel is injected into the cylinder at a high pressure of between 250 and 300 bar, with a minimum amount of pilot fuel and an injection angle close to the top dead center (TDC). This type of injection enables a dynamic response to the gas-oil combustion of the slow-speed MAN ME-C engine [35]. However, the differences in performance depend largely on factors such as load conditions. [7].