The objective of this experimental investigation was to analyze the effect of various exhaust gas aftertreatment technologies on particulate number emissions (PN) of an MPFI EU5 motorcycle. Specifically, three different aftertreatment strategies were compared, including a three-way-catalyst (TWC) with LS structure as the baseline, a hybrid catalyst with a wire mesh filter, and an optimized gasoline particulate filter (GPF) with three-way catalytic coating. Experimental investigations using the standard test cycle WMTC performed on a two-wheeler chassis dynamometer, while the inhouse particulate sampling system was utilized to gather information about size-dependent filtering efficiency, storage, and combustion of nanoparticles. The particulate sampling and measuring system consist of three condensation particle counters (CPCs) calibrated to three different size classes (SPN4, SPN10, SPN23). The study revealed that all three aftertreatment technologies were effective in reducing PN from the motorcycle, although the standard OEM LS honeycomb is already below the passenger car Euro 6 particle emission limits [1]. However, the GPF with a three-way catalytic coating showed the highest filtering efficiency with a significant decrease in PN emissions, particularly SPN10 and above, compared to the baseline. The hybrid catalyst with a wire mesh filter was also effective with a slightly better reduction in PN emissions compared to the baseline, but it had better backpressure behavior than the GPF and a significantly robust design. The reduction efficiency of the TWC was consistent with prior research. Moreover, the study highlighted the importance of considering the size distribution of particles when assessing aftertreatment strategies. The GPF and the hybrid catalyst with a wire mesh filter demonstrated high filtering efficiencies across all size classes. The TWC with LS structure was less efficient, particularly for the larger size classes, as previously reported [2].
In conclusion, this study emphasizes the need to consider both the overall reduction of PN and the size-dependent filtering efficiency of different aftertreatment strategies when assessing their effectiveness in reducing emissions from motorcycle exhaust.