Innovative Ring Catalyst for more Efficient NOx Reduction

• New Real Driving Emissions (RDE) legislation will strictly regulate NO_x emissions under all driving conditions, requiring high catalyst efficiency across a wide engine operating range
• Substantial reductions in nitrogen oxide emissions are also required by the US SULEV 30 emissions standard
• Close-coupled annular catalytic converter developed by Continental supports near-complete NO_x conversion in turbocharged gasoline engines

 
Vienna, Regensburg, Lohmar, April 14, 2016. The international technology company Continental has chosen the 37th Vienna Motor Symposium to present an innovative emissions control solution for downsized turbocharged gasoline engines. The introduction of Real Driving Emissions legislation will require vehicles with this widely used engine concept to meet strict nitrogen oxide (NO_x) limits in all driving situations. This poses a new challenge by demanding efficient NO_x 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. On the US front meanwhile, the LEV III SULEV 30 standards stipulate a 70% reduction in fleet-average nitrogen oxide emissions by 2025.

High-performance 3-way catalytic converters of today already achieve a NO_x reduction rate of 99%. But that still doesn’t go far enough, and a further efficiency hike must be targeted. For downsized turbocharged gasoline 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 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 nitrogen oxide emissions, a solution which comes at the price of additional weight and increased exhaust back pressure.

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°. 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,” says Rolf Brück, Head of Catalysts & Filters Product Line, Fuel & Exhaust Management. “With this design, the swirl effect from the turbocharger wastegate gas actually assists exhaust mixing in the internal pipe.”