A full-cylinder CFD model was developed to investigate methyl decanoate (MD)/diethyl ether (DEE) blends in a MAN B&W 7S80ME-C9 two-stroke diesel engine at 75% load. The model retained the multi-injector configuration, asymmetric spray development, scavenging and exhaust processes, and in-cylinder combustion of the 800 mm-bore engine. Four equal-energy cases, MD100, MD95, MD90, and MD85, were considered, with DEE energy fractions of 0%, 5%, 10%, and 15%. DEE blending regulated spray evaporation, mixture formation, heat-release phasing, and expansion work conversion. Increasing the DEE fraction enhanced evaporation and gas-phase mixing, but stronger mixing did not necessarily improve thermal performance. The peak-pressure trend differed from the net indicated work trend, indicating that work output was governed more by pressure evolution during expansion than by peak pressure alone. MD90 maintained stronger post-injection heat release and a more favorable equivalence-ratio distribution, thereby achieving the highest net indicated work, 6.70% higher than MD100. Although MD90 showed a high mean temperature, it produced the lowest NO and NO₂ emissions because NO_X formation depended on the local coupling of temperature, oxygen availability, equivalence ratio, and residence time. The CO₂ level was lowest for MD100 among the four fuel cases. At 75% load, MD90 provided a favorable balance among heat-release phasing, net indicated work, and emission control across the four investigated fuel cases.

Diesel engine emissions remain a concern because of their environmental and health impacts. Homogeneous charge compression ignition experiments on low-speed two-stroke marine diesel engines are costly, risky, and limited by scarce transient data. To address this issue, a one-dimensional/zero-dimensional AVL BOOST-ANSYS CHEMKIN coupled framework was established for an MAN B&W 6S50MC low-speed two-stroke marine diesel engine, providing a reasonable approach under data-limited conditions. The framework provided key initial conditions for detailed chemical-kinetic analysis and was used to examine methyl decanoate (MD)/di-n-butyl ether (DBE) blends with 0–20% DBE. The results indicate that DBE addition alters the balance between aromatic growth and oxidative removal and enhances low-temperature chain branching, while the increased peak temperature raises nitrogen oxides (NO_X) emissions. To relate these mechanistic results to engineering evaluation, the weighting scheme of the IMO NO_X Technical Code 2008 test cycle was introduced. Pyrene and its isomers and NO_X were treated by weighted normalization, followed by Pareto analysis and TOPSIS methods. MD90 (90 vol% MD and 10 vol% DBE) showed the best emissions trade-off over a wide range of weighting settings, which may provide useful guidance for optimizing oxygenated fuel blending ratios.