An Overall Comparison Between Natural Gas Spark Ignition and Compression Ignition Engines for a Ro-Pax Propulsion Plant

The paper presents a study concerning the repowering of an existing ro-pax operating across the Strait of Messina (Italy). Considering the short ferry routes (about 4 km) and the ship operating profile (24 hours/day of continuative operation), two different solutions are compared for the renewed propulsion engine system: traditional diesel four stroke engines (DE) and natural gas (NG) fueled marine engines. This second alternative is considered due to the better performance in terms of pollutant emissions and efficiency, if compared to DE of the same power and rotational speed, as verified by the authors in a recent paper. The different engines fuel types require different solutions for the fuel storage and handling that involve significant differences in the engine room layout, vessel structures, general arrangements, load capacity and ship stability. In the paper, all these subjects are analyzed for the considered propulsion power solutions, including also other important aspects as fuel, machinery and maintenance costs.