To reduce methane slip from marine gas engines installed in gas fuelled ships, it is necessary to understand the effects of exhaust composition and temperature on the activity of the methane oxidation catalysts in the marine gas engine exhaust. A comparative study was performed to evaluate catalyst performance in both actual engine exhaust and the simulated gas under the same flow conditions. The test using actual exhaust gas test showed that despite the lower exhaust temperatures during low load operation, the catalyst exhibited an extremely high performance, achieving approximately 100% CH4 conversion. In contrast, at high load, despite high exhaust temperatures, the CH4 conversion was decreased to 50-60%. In the simulated gas test showed that the catalyst’ activity was declined with increasing concentration of H2O and NO, whereas it was improved by CH4 and CO oxidation. The results showed that high CH4 concentrations under low load conditions enhanced catalyst activity owing to the exothermic reaction, which increased the catalyst temperature despite the low exhaust temperature and the presence of H2O vapour. Furthermore, during actual engine operation, the catalytic performance at a high load was improved by controlling the air excess ratio.
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