Importance

Loading Importance Indicators...

Abstract

A converter for purifying exhaust gases from lean-burn engines, in particular for controlling the amount of NO.sub.x and soot from a diesel engine in transient operation such as a vehicle. The converter contains a catalyst bed with a catalyst effective for NO.sub.x reduction with a chemical reductant when the catalyst bed is with a certain temperature window and when the ratio between the molar amount of chemical reductant and NO.sub.x is above a certain minimum ratio. The catalyst bed is heated or cooled to a temperature within the temperature window and a switching valve is provided for reverse flowing the exhaust gases through the converter to maintain the catalyst bed at a temperature within the temperature window for a longer time than is possible with a conventional non-flow-reversing converter. A reductant delivery system adds chemical reductant to the exhaust gases in an appropriate amount so that the ratio between the molar amount of chemical reductant and NO.sub.x is above the certain minimum ratio when the exhaust gases pass over the catalyst bed. A soot trap may be provided in series with the catalyst bed in the converter, said reverse flowing of the exhaust gases through converter heating and continuously maintaining the soot trap at or above the ignition temperature of the soot.

Loading the Abstract Image...

First Claim