Exhaust System for an Internal Combustion Engine

Abstract

An exhaust system ( 1 ) for an internal combustion engine ( 2 ), especially for a diesel engine, includes an exhaust manifold ( 3 ) inside which at least one exhaust aftertreatment device is disposed, and at least one DeNox unit that is arranged downstream from a first oxidizing catalyst ( 4 ). In order to reduce the NO x emissions a second oxidation catalyst ( 5 ) is disposed upstream of the DeNOx unit.

1 . An exhaust system ( 1 ) for an internal combustion engine ( 2 ), comprising an exhaust manifold ( 3 ) inside which at least one exhaust aftertreatment device is disposed, at least one DeNox unit arranged downstream from a first oxidizing catalyst ( 4 ), and a second oxidation catalyst ( 5 ) is disposed upstream of the DeNOx unit. 
   
   
       2 . The exhaust system ( 1 ) according to  claim 1 , wherein the first and second oxidation catalyst ( 4 ,  5 ) are configured for different activities and/or for different temperature ranges. 
   
   
       3 . The exhaust system ( 1 ) according to  claim 1 , wherein the first and second oxidation catalyst ( 4 ,  5 ) comprise different masses of noble metal, the second oxidation catalyst ( 5 ) having a larger mass of noble metal than the first oxidation catalyst ( 4 ). 
   
   
       4 . The exhaust system ( 1 ) according to  claim 1 , wherein the first and second oxidation catalyst ( 4 ,  5 ) are arranged parallel with respect to each other in the exhaust manifold ( 3 ) as regards flow, with the flow through at least one oxidation catalyst ( 5 ) being adjustable by means of an actuator ( 7 ). 
   
   
       5 . The exhaust system ( 1 ) according to  claim 1 , wherein a first and second oxidation catalyst ( 4 ,  5 ) are arranged in series in regard to flow in the exhaust manifold ( 3 ), with at least one oxidation catalyst ( 5 ) being capable of being bypassed via a bypass line ( 8 ), with an actuator ( 7 ) being arranged in the bypass line ( 8 ). 
   
   
       6 . The exhaust system ( 1 ) according to  claim 1 , wherein a first and second oxidation catalyst ( 4 ,  5 ) are arranged in a single housing. 
   
   
       7 . The exhaust system ( 1 ) according to  claim 1 , including a particulate filter ( 9 ) upstream of the DeNOx unit and downstream of a dosing device ( 10 ) for reducing agents. 
   
   
       8 . The exhaust system ( 1 ) according to  claim 5 , wherein the actuator ( 7 ) is adjustable in a model-based way depending on the NO x  content in the exhaust gas, the temperature of the exhaust gas, the pressure loss of the diesel particulate filter ( 9 ), the air-mass flow, the fuel-mass flow, or the crankshaft speed. 
   
   
       9 . The exhaust system ( 1 ) according to  claim 8 , including at least one NO x  sensor downstream of the DeNOx unit. 
   
   
       10 . A method for operating an exhaust aftertreatment system for reducing the nitrogen oxide emissions of an internal combustion engine, preferably an SCR catalyst, with a sensor for determining the NO x  concentration being arranged in the exhaust manifold downstream of the exhaust aftertreatment system, and with a reducing agent or an aqueous urea solution being dosed to the exhaust gas at a stoichiometric ratio to the NO x  emissions upstream of the exhaust aftertreatment system, and with the NO x  emissions of the internal combustion engine being determined by means of a characteristic map of the engine or an exhaust gas model, comprising measuring NO x  emissions beneath the minimum temperature of the exhaust gas and/or in operating phases where no reducing agent is added with the sensor downstream of the exhaust aftertreatment system and comparing obtained values based on the characteristic map or model, and performing a correction of the characteristic map or emission model in the case of a deviation between the measured values and those based on the characteristic map or model. 
   
   
       11 . The method according to  claim 10 , wherein a correction of the characteristic map or the model only occurs when an amount of the gradient of the speed and/or torque of the internal combustion engine lies beneath a predetermined threshold value. 
   
   
       12 . The method according to  claim 11 , wherein exhaust gas conveying time between the internal combustion engine and the sensor is taken into account in the comparison of the measured values of the NO x  emissions with those based on the characteristic map or model. 
   
   
       13 . The method according to  claim 12 , wherein the correction performed per correction step is smaller than a predefined permissible maximum value.