| dc.description.abstract | In order to alleviate global warming, governments and vehicle makers endeavor to suppress carbon dioxide emissions and clean up mobile exhaust gases at the same time. Therefore, many countries limited the vehicle emissions by more serious emission standard, especially for motorcycles. Although motorcycles have adopted new EMS (engine management system) from automobiles, better fuel economy and less emission are still needed. The gasoline fuel lean-burn engine is one solution to enhance the fuel efficiency of vehicles. However, the A/F of the lean-burn engine is usually controlled above 18-22, it is difficult to reduce the NOX emission with the conventional catalyst of vehicle at this high A/F. To address the conflict of high fuel efficiency and low NOX emissions, a possible solution involves the use of a NOX storage reduction (NSR) catalyst in combination with mixed-lean engine operation.
In this study, Pt/Al2O3 and Pd/Al2O3 are used as the conventional catalyst, while Pt/Ba/Al2O3 and Ba/Pd/Al2O3 are used as NSR catalyst after adding Ba. Experimental results indicate the BET surface areas of NSR catalyst were slightly smaller that of the conventional catalyst. The dispersion of Pt/Al2O3 and Pt/Ba/Al2O3 were obviously better than that of Pd/Al2O3 and Ba/Pd/Al2O3, indicating the dispersion of Pt/Al2O3 was increased by adding Ba. However Ba/Pd/Al2O3 has a different trend. It may be due to different preparation methods. Pt/Ba/Al2O3 impregnated Ba and Al2O3 in first step and caused the support (Al2O3) surface variation, but the Ba/Pd/Al2O3 impregnated the Pd and Al2O3 ahead. Hence, the dispersion degree was not effectively increased by adding Ba.
The activity of NSR was improved by adding Ba, and the NOX conversion achieved with NSR catalyst (Pt/Ba/Al2O3) decreased with increasing temperature, However, the activity of Ba/Pd/Al2O3 increased with increasing temperature, the light-off temperatures of conventional catalyst were higher than NSR catalyst. Conversions of HC and NOX achieved with Pt/Ba/Al2O3 and Ba/Pd/Al2O3 were higher than that of Pt/Al2O3 and Pd/Al2O3, respectively, with A/F below 14.5, and the conversions of CO were similar in different A/F.
In the real application to the vehicle, the CO and HC conversions achieved with NSR catalyst Pt/Ba/Al2O3 and Ba/Pd/Al2O3 increased about 12~13% compared with conventional catalyst. The reason should be the lower light-off temperature to make the pollutant convert earlier. The NOX conversion of Pt/Ba/Al2O3 catalyst was superior to Pt/Al2O3 by 12%, but the NOX conversion of Ba/Pd/Al2O3 just increased by 4.5% compared with Pd/Al2O3.
This research proved that the NSR catalyst could improve the NOX conversion in lean-burn engine of motorcycle, but it is still needed to switch A/F to rich region at right time to improve the performances.
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