Strategies for Emission Reduction on Small Capacity Two-Wheelers with Regard to Future Legislative Limits

Looking at upcoming emission legislations for two-wheelers, it is quite obvious that the fulfilment of these targets will become one of the biggest challenges within the engine development process. The gradual harmonization of emission limits for two-wheelers with existing automotive standards will subsequently lead to new approaches regarding mixture preparation and exhaust gas aftertreatment. Referring to these future scenarios, a state-of-the-art in development of catalytic converters for two- or three-wheeler applications should be presented.
After choosing a suitable test carrier, which has already been equipped with EFI components including an oxygen sensor for λ=1 operation mode, a basic injection system calibration was used to optimize the combustion process. Based on this setup, a variable exhaust system was manufactured to be able to integrate different catalyst configurations. To improve cold start characteristics, the position of the lambda probe and the catalyst were optimized to achieve short light-off times. Thus, the possibility for investigations on exhaust gas aftertreatment was given. Initially, the vehicle was operated with a metallic foil monolith without precious metal coating to identify the level of untreated emissions under comparable conditions with regard to backpressure in the exhaust system. In succession, different precious metal and washcoat loadings were tested with the same monolith structure to get insight in the individual conversion behavior. Hence, an optimized configuration in terms of exhaust gas aftertreatment capabilities was derived. These investigations should serve as a basis to illustrate the emission reduction potential of small capacity two-wheelers by means of technological improvements, paying attention to the upcoming EURO 4 and EURO 5 legislation. Finally, a possible system cost reduction was contemplated. Starting from the most sophisticated setup, a reduction of cell density was investigated. Therewith, low-cost configurations were derived that could be of interest for applications being subject to less stringent emission regulations.