Marinization process of a prototype hybrid power unit

This thesis aims to describe the activities I carried out during my curricular internship at Oral Engineering S.R.L. in Modena. The paper begins by analyzing the international legislation on emissions produced by both recreational craft and ships. Over the last decade, both European and US legislators have tightened the limits on these pollutant emissions and the related control methods to such an extent that engine manufacturers have been forced to adopt after-treatment systems that are sometimes incompatible with achieving certain specific power ratings and/or particular applications for their engines. This has led to the need for alternative solutions, such as hybrid power units. I decided, then, to review the existing solutions in literature, starting with some ingenious hybrid solutions that appeared on prototype submarines as early as the end of the 19th century up to the beginning of the 20th century with the advent of diesel-electric propulsion systems on both submarines and those peculiar ships where navigation autonomy, low fuel consumption, and rapid maneuverability provided by electric propulsion were characteristics of primary importance (for example icebreakers, offshore supply ships, river barges etc.) Finally, a descriptive overview of modern hybrid propulsion solutions was provided, starting with the avant-garde Slovenian Greenline 33 cabin cruiser, moving on to the Japanese Yanmar's YF12e hybrid serial system, and ending with the latest and more sophisticated European parallel hybrid systems offered by MAN and Volvo Penta. I wrote, then, a technical description of the Oral D2L26H prototype: a hybrid power unit consisting of a 2600 cm^3 turbocharged inline two-cylinder diesel engine capable of developing 173 kW at 3250 rpm and an axial flow electric motor mounted on the crankshaft (P2 parallel hybrid configuration) which, at 2200 rpm, adds 125 kW of power to the total power unit. An electric-actuated clutch provides the mechanical linkage between the two units. In May 2025, the power unit entered one of the Oral test cells. It was tested without the electric motor, though, as the Oral test cell was not equipped with a battery emulator: for the characterization of the electric motor, it was decided to rely on testing carried out by LUCCHI R, the motor manufacturer. The engine, equipped with its sensors and actuators, was then installed on the test bench. The necessary bench sensors were connected and calibrated to safeguard the mechanical functionality of the engine (engine oil temperature and pressure, engine coolant temperature, fuel pressure, temperature and pressure upstream and downstream of the intercooler, temperature and pressure upstream and downstream of the turbocharger, air/fuel equivalence ratio from oxygen sensors, combustion chamber pressure and so on). Cold runs were then conducted to check for any mechanical issues and to ensure that the correct oil pressure was achieved before proceeding with the first actual engine run. After that, the engine break-in phase and the first basic calibration began, finally leading to the definition of the power curve. Thanks to the data collected during the testing phase, I was able to begin my work of marinization, deciding component by component what needed to be added and what needed to be replaced in order to install the engine in a recreational craft. The first steps involved selecting a filter box suitable for a boat's engine room, planning anti-corrosive painting for the entire unit, and replacing the Garrett VGT with a fixed-geometry turbocharger, which is more suitable for the operational use of a marine engine. The final part of my work then focused on designing and sizing the cooling circuit for the entire power unit, which is the system that differs most from its equivalent for vehicle use.