In the present work, the combustion process of a retrofitted high-speed marine Diesel Methanol Dual Fuel (DMDF) engine is numerically evaluated. This study examines the effects of two important operational parameters, the methanol energy substitution ratio (MESR) and diesel injection timing, with a focus on engine performance and emissions. To perform the analysis, a CFD numerical combustion model was developed, and a mean value model, along with other data-driven models, were employed to estimate the intake cylinder conditions. The numerical models were calibrated and validated using experimental data measured at the DMDF experimental testbed at the Laboratory of Marine Engineering (LME). The models were utilized to conduct a parametric study considering various engine speeds and loads, diesel injection timings, and MESRs up to 75%. The impact of these parameters was quantified with respect to in-cylinder pressure, ignition timing, combustion efficiency, NO_x, soot, and HC emissions. The results revealed that an increased methanol ratio leads to delayed ignition timing, shorter combustion duration, and reduced in-cylinder peak pressure and combustion efficiency. NO_x and soot emissions are also reduced, whereas the concentrations of unburned hydrocarbons in the exhaust gas increase significantly and mainly consist of Volatile Organic Compounds (VOCs). Although advancing injection timing in dual-fuel mode improves combustion efficiency, it increases the maximum in-cylinder pressure and NO_x emissions. The other emissions are either reduced or maintained at the same levels. Moreover, the results suggest that there is a trade-off between NO_x emissions and combustion performance, which must be taken into account when the operational parameters are adjusted for these engines. Finally, the maximum MESRs are estimated to ensure safe combustion within acceptable peak pressure limits and adequate combustion performance.

This work addresses the design and experimental implementation in real-time of an integrated predictive load-split management system for the transient and fluctuating propeller load sharing. Control-oriented modeling of the power system was performed based on experimental data gathered from the hybrid plant and on first principles for the diesel engine behavior and battery charging. Propulsion plant and environmental disturbance models are developed to simulate realistic marine load application. A nonlinear model predictive control (NMPC) scheme is proposed for the optimal transient power-split problem of a hybrid diesel-electric marine propulsion plant. The NMPC scheme directly controls the torque output of the diesel engine and the electric motor/generator ensuring that certain constraints concerning the system overloading are met, avoiding fast accelerations and load fluctuations of the diesel engine that affect engine performance. To achieve offset-free model predictive control (MPC) control, an observer is developed to provide the propeller law parameter to the NMPC for load estimation. The control system was experimentally tested in real-time operation. Results showed that controller rejected load disturbances and maintained the desired rotational speed of the powertrain as well as the desirable state of charge (SOC) in battery within the power plant limits, achieving smooth power transitions and mitigation of power fluctuations of the diesel engine.