会議名: The 10th International Conference on Modeling and Diagnostics for Advanced Engine Systems (COMODIA 2022)
開催日: 2022/07/05 - 2022/07/08
In the maritime industry, marine lean-burn gas-engines have been expected to reduce emissions such as NOx, SOx and CO2. The methane slip, which is the unburned methane emitted from marine gas-engines has raised concern because of its impact on global warming. Because the number of the gas fuelled ships is increasing worldwide, the resulting increase in methane slip is now becoming a threat. It is therefore important to make a progress on the exhaust aftertreatment technologies for marine gas-engines. A methane oxidation catalyst supported the platinum group metals, especially palladium exhibits highest activity for CH4 oxidation in lower temperature, can be expected to be one of the most feasible countermeasures for the methane slip. Research and development on catalysts as aftertreatment has focused mainly on reducing emissions in natural gas vehicles. However, exhaust gas of the marine gas-engine is different from that of natural gas vehicles, such as lower temperature, and emission composition corresponding to widely use of engine load ranges. To apply the catalyst for the marine gas-engine, it is important that, in order to predict the catalyst performance considering exhaust gas components, the investigation on the effects of exhaust composition and exhaust temperature on the catalyst activity by comparing in actual exhaust gas of marine gas-engine and the simulated gas. Although the effects of specific exhaust composition, such as water on the catalyst activity are investigated in detail, the effects of comprehensive exhaust compositions are unclear. On the other hand, it also cannot be found the research on the performance of the catalyst under actual exhaust conditions coincident to a wide range of load conditions of marine gas-engines. Therefore, for the practical use of the catalyst, a comparative study on the catalyst performance evaluation in the actual engine exhaust gas and the simulated gas under same flow condition is necessary.
The actual exhaust gas test reveals that, despite lower exhaust temperature in low load condition, the catalyst exhibits extremely high performance nearly 100% CH4 conversion. In contrast, despite higher exhaust temperature in high load condition, the catalyst activity on CH4 conversion is reduced to 50%-60%. The simulated gas test shows that the catalyst activity is deactivated with increasing H2O and NO concentration and improved by CH4 and CO oxidation. Moreover, the results explain that high CH4 concentration in low load condition causes an increase of catalyst temperature and high catalyst activity by exothermic reaction, despite the low exhaust temperature and presence of H2O vapor. Because the measurement of NO adsorption on the catalyst at exhaust temperature exhibits that NO adsorption volume decreases with increasing temperature, NO adsorption can be one of the causes of catalyst deactivation especially at lower exhaust temperature.