Continental has chosen the 37th Vienna Motor Symposium to present an innovative emissions control solution for small size turbocharged engines. The introduction of more strict exhaust emissions legislation, which requires vehicles, to meet ever lower nitrogen oxide (NOx) levels at all rpm in the rev range. This poses new challenge by demanding efficient NOx reduction across a very broad spectrum of engine operating conditions, and not 'just' in the current test cycles.
However, the existing close-coupled catalytic converters of today offer little margin for any further improvements in lambda distribution.
In order to meet future exhaust emission legislation on NOx emissions, a 3-way catalytic converter must achieve a conversion rate close to 100%. That is only possible, if efficient NOx reduction is maintained uniformly in all operating situations. The innovative ring catalyst in combination with Continental's LS microstructured metal foil will be an important part in meeting the future emission requirements. High-performance 3-way catalytic converters of today already achieve a NOx reduction rate of 99. But that still doesn't go far enough, and a further efficiency hike must be targeted. For downsized turbocharged engines, this presents two challenges. Firstly, cylinder-to-cylinder variations in exhaust gas composition mean that the fuel-to-air ratio (lambda value) can deviate from the ideal value, adversely affecting NOx conversion. The aim must be to avoid such cylinder influences on exhaust lambda, by flow mixing. However, this is difficult in the case of a close-coupled catalytic converter, because the down pipe to the catalytic converter is not long enough.
Secondly, in some operating situations, the catalytic converter's ability to achieve a consistent and uniform NOx conversion rate can be adversely affected by the turbocharger system. This is because the opening of the turbine bypass valve (wastegate) above a certain engine speed affects the flow distribution, resulting in non-uniform exhaust flow. This can potentially lead to faster local aging of the catalytic converter and to a deterioration in NOx reduction performance.
Continental has developed an innovative solution to address both these challenges: The ring catalyst. An internal pipe running through the core of the ring catalyst and all the way along it provides the necessary additional length to allow better exhaust flow mixing. At the end of this pipe the gas is redirected through 180 degree. Only then does it flow through the catalytically active portion of the catalyst, which surrounds the inner pipe like a sleeve. This way the annular catalyst extends the flow path without extending the overall length of the catalyst. This allows the catalyst to be mounted closer to the engine, so there is no increase in the time required to reach light-off temperature for converting NOx emissions. With this design, the swirl effect from the turbocharger wastegate gas actually assists exhaust mixing in the internal pipe.