Impact of 3-way catalytic converters on particulate emission of MPFI motorcycle engines

Due to climatic movements and politics, there is no doubt that a stricter emission legislation will soon face the two-wheeler sector and their manufacturers with new challenges. Additional to the already limited pollutants, a limitation of particulate number will probably also be introduced, which means that there is an urgent need for action in exhaust gas aftertreatment and particulate reduction systems. For natural aspirated, port injected engines, as used in two-wheeler-technologies, conventional systems already established in passenger cars are
not necessarily applicable. Moreover, the emission spectrum is fundamentally different from passenger car engines due to the better homogenization of they typically used MPFI engine types. Adapting conventional particulate filter technologies to the finer particles of MPFI engines would result in a disproportionately larger exhaust backpressure. For this reason, we are investigating the effects of 3-way catalytic converters on particulate number emissions from MPFI engines in the two-wheeler sector and possible modifications to increase filtration and particulate burn-off. The characteristic properties of the catalyst investigated in this context relate to cell density, honeycomb construction, foil technologies and coatings and their effect on the emission behaviour of particles of different size classes. Initial investigations showed that the 3-way catalyst has significant influence on particle emission due to its design and exothermic reactions. An adjustment of the already mentioned characteristics of the catalyst shows further reduction possibilities especially for ultrafine
particles smaller than 10 nm. With increasing size and the accompanying bigger thermal inertia of the particles, the reduction potential decreases sharply within a few nanometres.