Close-coupled annular catalytic converter developed by Continental supports near-complete NOx conversion in turbocharged gasoline engines. Click to enlarge.

However, the existing close-coupled catalytic converters of today offer little margin for any further improvements in lambda (air-fuel equivalence ratio, the ratio of the actual Air-Fuel Ratio (AFR) to stoichiometry for a given mixture) distribution, Continental says. On the US front, the LEV III SULEV 30 standards stipulate a 70% reduction in fleet-average nitrogen oxide emissions by 2025.

In order to meet RDE and SULEV 30 legislation on NO_x emissions, a 3-way catalytic converter must achieve a conversion rate close to 100%. That is only possible, if efficient NO_x reduction is maintained uniformly in all operating situations. The innovative ring catalyst in combination with our LS micro-structured metal foil will play an important role in meeting this requirement.

—Dr. Markus Distelhoff, Executive Vice President Fuel & Exhaust Management Business Unit in Continental’s Powertrain Division

High-performance 3-way catalytic converters of today already achieve a NO_x reduction rate of 99%. However, that doesn’t go far enough, and a further efficiency hike must be targeted.

For downsized turbocharged gasoline engines, this presents two challenges.

1. Cylinder-to-cylinder variations in exhaust gas composition mean that lambda can deviate from the ideal value, adversely affecting NO_x 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. This is why many new vehicles now feature a second underfloor catalyst to convert the remainder of the NO_xemissions, a solution which comes at the price of additional weight and increased exhaust back pressure.

2. In some operating situations, the catalytic converter’s ability to achieve a consistent and uniform NO_x conversion rate can be adversely affected by the turbocharger system. 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 NO_x reduction performance.

Continental’s ring catalyst addresses both these challenges. 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°. 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 placed close to the engine, so there is no increase in the time required to reach light-off temperature for converting NO_x emissions. With this design, the swirl effect from the turbocharger wastegate gas actually assists exhaust mixing in the internal pipe.

—Rolf Brück, Head of Catalysts & Filters Product Line, Fuel & Exhaust Management

The core of the catalytic converter is wound from “LS” metal foil, a material developed by Continental. Longitudinal structures (LS) in this foil or substrate create more turbulence in the exhaust gas. This ensures better contact between the nitrogen oxides and the catalytically coated substrate, resulting in higher conversion efficiency. Click to enlarge.

The active section of the ring catalyst is wound from Continental’s innovative LS metal substrate. The longitudinal structures in this material generate micro-level turbulence in the exhaust stream, which helps to direct the nitrogen oxides more effectively towards the catalytically coated catalyst wall, where they are converted.