Exhaust Gas Treatment in Marine Compression Ignition Engines: Design and Efficiency Assessment of a Wet Scrubber System

Abstract Under MARPOL, PM and NOx from marine engines are controlled, whereas HC is not explicitly regulated. PM is mainly managed indirectly through limits on fuel sulphur content, known as the global sulphur cap. In addition, regional frameworks such as EU imposes further limits on marine engines, while NOx is addressed through Tier I-III standards. In response to increasingly stringent emission requirements, this study evaluates the feasibility and design optimization of a wet scrubber for diesel engine exhaust treatment. High-speed shadowgraph imaging was applied to investigate multiphase interactions within the scrubber. The experimental system employed a Photron Fastcam operating at up to 200,000 fps, combined with a high-frequency LED and a 120-grit ground glass-diffuser to ensure uniform backlighting. Micro lenses provided spatial resolutions as fine as 3.8 μm/pixel, enabling detailed characterization of spray dynamics, including cone angle, droplet size distribution, and liquid sheet breakup length. Quantitative analysis was conducted using ImageJ-based statistical processing. The optimized design minimized unfavorable spray-spray and spray-wall interactions, improving gas-liquid contact efficiency. Experimental results achieved soot removal efficiencies of up to 70%, primarily through impaction and coagulation mechanisms. Optimal performance occurred at 75% engine load with a liquid-to-gas ratio of 5 L/Nm3. However, gaseous pollutant removal remained limited, with maximum reductions of 15% for NOx using NaClO2 and 4% for HC. These findings support effective soot abatement while highlighting the need for hybrid or catalytic solutions to achieve comprehensive emission compliance.