Integration and optimization of the after-treatments systems to reduce the acoustic footprint of the ships

Exhaust Gas Cleaning Systems (EGCS) such as scrubbers are mandatory and extensively used to abate SOx in exhaust gases when high sulphur content fuel oil is employed in the marine engine in order to comply with international ship emission regulations, both in new and existing ships. Currently, about 13% of bulker, container, and tanker ships have a scrubber installed, despite the fact that their installation on board is challenging due to their large dimensions to be fitted into the funnel and the complexity of the system, since the exhaust line must control both the chemical and acoustic emissions. In the presented work a combined FEM, CFD simulations and GA optimization methodology aimed at the integration of the abatement system, while optimizing the acoustic properties, is developed. The methodology is first assessed on an industrially-relevant scenario that involves the use of a Genset mock-up equipped with a reference Diesel Oxidation Catalyst (DOC) and a scrubber for the abatement of both NOx and SOx, showing that acoustic performances of the DOC are reliably modelled by the FEM-CFD methodology, which has a significantly reduced computational cost as compared to conventional CFD modelling of acoustic properties. The GA optimization is carried out to improve the DOC acoustic properties showing that it is possible to confer the silencing effect to the after-treatment systems, thus eliminating the traditional silencers from the exhaust line. This leads to a compact exhaust line that integrates the EGCS while maintaining efficient both the chemical pollution abatement capability, and silencing effects to guarantee full compliance (i.e., acoustic and chemical) with the international regulations.