Browse Publications Technical Papers 1999-01-1328
1999-03-01

Possible Exhaust Gas Aftertreatment Concepts for Passenger Car Diesel Engines with Sulphur-free Fuel 1999-01-1328

In order to fulfill future emissions standards, there is a need for new exhaust-gas aftertreatment concepts, with NOx-emissions reduction in passenger car diesel engines being of particular importance. The NOx storage catalyst is one of the technologies currently under discussion with high NOx conversion potential, and which is under development at DaimlerChrysler for EURO IV standards. With this system, the nitrogen oxides contained in the diesel exhaust gas are stored under lean exhaust-gas conditions and are reduced in the catalyst through an enriched air-fuel ratio of the exhaust-gas and favorable thermal conditions. Hydrocarbons, carbon monoxide and hydrogen are used as reducing agents.
DaimlerChrysler has analyzed the effect of sulphur contained in the fuel on the operation of various catalysts during laboratory and engine testing. The sulphur dioxide in the exhaust gas generates sulfates, which remain on the catalyst when nitrate compounds are regenerated briefly. For this reason, NOx conversion efficiency deteriorates rapidly. Using the diesel fuel currently available in Europe with a sulphur content of 370 ppm (limit: 500 ppm), the efficiency of the catalyst is significantly reduced within a few operating hours.
However, using diesel fuel with a sulphur content of 10 ppm in a C220 CDI fitted with a NOx storage catalyst, a potential for NOx reduction in the New European Driving Cycle (NEDC) of over 50% could be achieved in repeated testing.

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