Evaluation of different exhaust aftertreatment configurations for engines running with methanol

The maritime sector is a significant contributor to global greenhouse gas emissions. One potential solution to reduce these emissions is the adoption of green methanol (MeOH) as an alternative fuel. For safety reasons, marine engines must be capable of operating as dual fuel systems. When running in the Diesel mode, a selective catalytic reduction (SCR) system is necessary to reduce the emissions. However, when MeOH is used as fuel, the SCR catalyst reacts with the feed, forming unwanted products. To eliminate, suppress or prevent their formation, the integration of an oxidation catalyst is required. For this, two setups and two oxidation catalysts were evaluated across three different combustion modes. The two setups differ in the position of the oxidation catalyst, which was located either upstream or downstream of the SCR unit. The combustion modes consisted of one Diesel mode and two Dual Fuel PFI modes, which were synthetically reproduced based on exhaust emissions of real engines. Furthermore, a conventional Pt oxidation catalyst was evaluated and compared with a modified ammonia slip catalyst (ASC). The goal was to identify an exhaust aftertreatment configuration which is able to sufficiently remove or prevent the formation of all unwanted products for all combustion modes while complying with all essential maritime regulations.