Επίδραση της ενεργειακής υποκατάστασης με υδρογόνο στην καύση, τις εκπομπές και την τριβολογία του πρώτου ελατηρίου συμπίεσης ναυτικού κινητήρα diesel–υδρογόνου διπλού καυσίμου

The maritime sector is under increasing pressure to reduce greenhouse-gas (GHG) emissions and its dependence on conventional fossil fuels. Hydrogen is considered a promising alternative energy carrier because it contains no carbon and can be introduced into existing compression-ignition engines through dual-fuel operation. However, hydrogen substitution affects not only combustion and emissions, but also the mechanical and tribological loading of engine components. The present study investigates these combined effects in a Caterpillar C32 Marine ACERT diesel engine. A coupled computational methodology was developed using ANSYS Forte, Microsoft Excel and ANSYS Fluent. Four operating cases were examined: baseline diesel operation and diesel–hydrogen dual-fuel operation with 20%, 30% and 50% hydrogen energy substitution. The total nominal fuel energy per cycle was maintained constant between the investigated cases. The combustion simulations were performed in ANSYS Forte at 1800 rpm, with hydrogen introduced as a premixed component of the intake charge and diesel directly injected into the cylinder. In the dual-fuel cases, the diesel start of injection was changed from −8°CA to −6°CA. The combustion results showed that increasing hydrogen substitution significantly changed the in-cylinder process. The maximum cylinder pressure increased from approximately 18.83 MPa for the baseline diesel case to 25.05 MPa for the DF 50% H₂ case, while the crank angle of peak pressure shifted from approximately +10°CA to +5°CA. The maximum mean in-cylinder temperature increased from approximately 1877 K to 2316 K, while the apparent heat-release rate became substantially faster and more concentrated near top dead center. Hydrogen substitution strongly reduced soot and unburned hydrocarbon emissions, while carbon monoxide was also reduced at the higher substitution levels. In contrast, nitrogen-oxide emissions increased significantly, with the highest EINOₓ value obtained for the DF 50% H₂ case. The combustion results were subsequently transferred to a tribological model of the first compression ring. Ring kinematics and radial loading were calculated in Microsoft Excel, while a two-dimensional thermal lubricant-film model was developed in ANSYS Fluent using temperature-dependent lubricant viscosity and viscous heating. Asperity contact was evaluated using the Greenwood–Tripp model. Four characteristic crank-angle positions were examined for each fuel case, resulting in sixteen quasi-static tribological operating points. The minimum lubricant-film thickness was determined through an iterative load-balance procedure between the applied ring load, the hydrodynamic load and the asperity-contact load. At peak cylinder pressure, the total radial ring load increased from approximately 72.6 kN/m for the baseline diesel case to 96.4 kN/m for the DF 50% H₂ case. At the same time, the minimum lubricant-film thickness decreased from approximately 0.165 μm to 0.107 μm, while the film parameter, Λ, decreased from approximately 0.413 to 0.267. Overall, the results demonstrate a clear trade-off associated with hydrogen substitution. Hydrogen can strongly reduce soot and other carbon-based emissions, but high substitution levels increase combustion pressure, temperature and NOₓ formation and result in more severe first compression-ring lubrication conditions. Therefore, the application of hydrogen in marine diesel engines should be evaluated through an integrated consideration of combustion, emissions and tribological behavior.