Compression ignition engines used as marine engines are the most efficient internal combustion engines. They are well-established products, and millions are already on the market. Water-in-MDO (marine diesel oil) emulsions are the best alternative fuel for compression ignition engines and can be utilised with the existing setup of 2.0 L automotive common rail direct injection (CRDI) engines. They have benefits for the simultaneous reduction of both NO_x and smoke (black carbon). Furthermore, they have a significant impact on the improvement of combustion efficiency. Micro-explosions are the most important phenomenon of water-in-diesel emulsions inside an internal combustion engine chamber. They affect both the emission reduction and combustion efficiency improvements directly and indirectly in accordance with the brake mean effective pressure (BMEP) and rpm. Owing to the influence of micro-emulsions on the combustion and emissions of water-in-diesel emulsion fuel, the reduction ratios of NO_x and smoke in a used engine are approximately 30% and 80%, respectively. The effect of the operating parameters on micro-emulsions is presented.

Exhaust gases from ships and automobiles have a significant impact on people and the environment. As a result, diesel engines used in land and marine vehicles are gradually being restricted, and low-carbon engines are under development. This study considers marine diesel oil (MDO) that is used in ships to meet the emission regulations required by the International Maritime Organization. This investigation explores the method and application technology for the reduction of nitrogen oxides (NO_x) and particulate matter using emulsified fuel and mass-produced dimethyl ether (DME) fuel, which are analyzed. When comparing emulsified fuel and DME fuel to MDO, which is a ship oil, NO_x are reduced by 20–45% and the particulate matter is reduced by 60–97%. When emulsified fuel containing moisture is used, the combustion chamber temperature is lowered due to the optimal expansion by moisture contained in the fuel. The particulate matter is also reduced. When DME fuel is used, it reduces the particulate matter by more than 97% in comparison with the existing MDO fuel and the emulsified fuel. The conditions are believed to be suitable for combustion and they can be satisfied by supplying oxygen during post-combustion.

Currently, the exhaust gas of a ship is regulated for nitrogen oxides and sulphur compounds; however, there is no IMO regulation on smoke under discussion. This study investigated the reduction of exhaust gas through ship emulsion fuel, which can simultaneously reduce nitrogen oxides and smoke in ship engines before smoke regulations are established. The combustion and exhaust characteristics were investigated according to the moisture content of emulsion fuel using a 400-kW generator engine. As the water content of the emulsion and the temperature of the combustion chamber increase, micro explosion increases and the combustion period decreases. The nitrogen oxide and smoke from the emulsion fuel used in this study decreased by 7% and 75%, respectively. The nitrogen oxides and soot reductions obtained by the use of emulsion fuel were boosted by micro-explosion of water contained in the fuel during combustion.

Many researchers have conducted experiments on the position and nozzle conditions in the exhaust pipe of a stage/swirl mixer, as well as the injection position required to satisfy the International Maritime Organisation (IMO) regulations. In this study, an SCR (Selective catalytic reduction) system was designed through basic and detailed designs. The performance of the components was verified through a single-component performance test for the detailed design components, and the total nitrogen oxide (NOx) reduction efficiency was predicted using the proven system. Subsequently, the system was applied to an actual engine, and the performance was verified according to the engine operating conditions using the experimental variables. The NOx reduction rate and NH₃ slip characteristics in relation to MCR (Maximum Continuous Rating) conditions using the optimised SCR system indicate that the NOx reduction rate exceeds 80% in all MCR conditions. Finally, the SCR system developed in this study proves that the performance of the SCR system satisfies the IMO regulatory requirements.