A method for monitoring a gas sensor (14) which comprises two electrochemical measuring cells (20, 30) and which is arranged in an exhaust tract (10) of an internal combustion engine (11), wherein the sensor elements (20, 30) exhibit a substantially identical sensitivity towards a first gas component and a different sensitivity towards a second gas component and are insensitive towards further gas components. In an operating state in which an exhaust gas stream at the gas sensor (14) contains less of the second gas component than of the first gas component a concentration of the first gas component is calculated from each of the sensor signals from the sensor elements (20, 30) and a defect in a sensor element (20, 30) is deduced from the concentrations of the first gas component.

A catalyst article including a substrate with an inlet end and an outlet end, a first zone and a second zone, where the first zone comprises: a) an ammonia slip catalyst (ASC) bottom layer comprising a platinum group metal on a support; and b) an SCR layer comprising a second SCR catalyst, the SCR layer located over the ASC bottom layer; where the second zone comprises a catalyst (second zone catalyst) selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC); wherein the ASC bottom layer extends into the second zone; and where the first zone is located upstream of the second zone. The ASC bottom layer may include a blend of: (1) the platinum group metal on a support and (2) a first SCR catalyst.

An exhaust gas purification system and an exhaust gas purification method are disclosed. The exhaust gas purification system is provided with: an injector for injecting urea water, said injector being installed between a combustion device and a selective catalytic reduction (SCR) catalyst; a first gas sensor which is installed downstream of the SCR catalyst, and which detects the NO concentration and the NH.sub.3 concentration in exhaust gas outputted from the SCR catalyst; and an opening amount control means for controlling the opening amount of the injector for injecting urea water.

When an abnormality diagnosis of an SCR catalyst is carried out, diagnostic supply control is carried out in such a manner that the first estimated adsorption amount, which is an amount of adsorption of ammonia in the SCR catalyst at the time when the SCR catalyst is assumed to be in a predetermined abnormal state, becomes equal to or more than a first predetermined adsorption amount, and the second estimated adsorption amount, which is an amount of adsorption of ammonia in the SCR catalyst at the time when the SCR catalyst is assumed to be in a predetermined normal state, becomes smaller than a second predetermined adsorption amount. Then, supply decreasing control to decrease an amount of adsorption of ammonia in the SCR catalyst is carried out, after the end of the execution of the diagnostic supply control.

A catalyst article including a substrate with an inlet side and an outlet side, a first zone and a second zone, where the first zone includes an ammonia slip catalyst (ASC) comprising a platinum group metal on a support and a first SCR catalyst; where the second zone includes a catalyst selected from the group consisting of a diesel oxidation catalyst (DOC) and a diesel exotherm catalyst (DEC); and where the first zone is located upstream of the second zone. The first zone may include a bottom layer with a blend of: (1) the platinum group metal on a support and (2) the first SCR catalyst; and a top layer comprising a second SCR catalyst, the top layer located over the bottom layer.

A urea injection control method in an exhaust after-treatment system includes: performing an ammonia slip prevention logic that adjusts a urea injection amount based on the highest temperature during a predetermined period of time from an end point of filter regeneration to a thermal equilibrium point when a temperature of a selective catalytic reduction (SCR) catalyst is higher than or equal to a predetermined threshold temperature at the end point of the filter regeneration; and adjusting a urea injection amount based on an ammonia storage amount map when the temperature of the SCR catalyst is lower than or equal to the predetermined threshold temperature at the end point of the filter regeneration. In particular, the thermal equilibrium point is a point at which a temperature of a filter is close or equal to an exhaust gas temperature.

Systems and apparatuses include an apparatus including an aftertreatment system control circuit structured to receive a signal indicative of an exhaust gas characteristic from a sensor, determine an aftertreatment system characteristic based on the exhaust gas characteristic, determine an acceptable input value responsive to the aftertreatment system characteristic, and control at least one of a fuel system actuator and an air handling actuator to achieve or substantially achieve the acceptable input value.

Various embodiments include a method of operating a diesel engine having an exhaust tract and an SCR-combined diesel particulate filter in the exhaust tract, wherein an aqueous urea solution is introduced into the exhaust tract, and an exhaust gas recirculation apparatus having an exhaust gas recirculation conduit branching off downstream of the SCR-combined diesel particulate filter for performing a low-pressure exhaust gas recirculation comprising: measuring an NH.sub.3 concentration in exhaust gas downstream of the SCR-combined diesel particulate filter; and upon exceeding a threshold value of the measured NH.sub.3 concentration, reducing the low-pressure exhaust gas recirculation rate based at least in part on the measured NH.sub.3 concentration.

An exhaust treatment device for a diesel engine includes a parked regeneration requirement notification component, and a parked regeneration start operation component, a regeneration process of a diesel particulate filter includes an automatic regeneration process and a parked regeneration process, the automatic regeneration process is automatically started when an estimation value of particulate material accumulated in the diesel particulate filter reaches a predetermined value, and the parked regeneration process is performed when first and second conditions are satisfied, the first condition being that a parked regeneration requirement notification component performs a notification of a parked regeneration requirement when a number of cancellations of the automatic regeneration process reaches a predetermined value or more, the second condition being that the parked regeneration start operation component is subjected to a start operation during a parked state in which an engine equipped machine is neither traveling nor working.

A method includes interpreting NOx data indicative of an amount of NOx exiting an engine and an amount of NOx exiting an exhaust aftertreatment system coupled to the engine, determining a NOx conversion efficiency fault is present based on the amount of NOx exiting the engine and the amount of NOx exiting the exhaust aftertreatment system, and determining at least one of a selective catalytic reduction (SCR) catalyst of the exhaust aftertreatment system and a diesel particulate filter having a coating of a SCR reaction catalyst (DPF-SCR) of the exhaust aftertreatment system are responsible for the NOx conversion efficiency fault based on at least one of a reductant slip amount and a NOx conversion value across at least one of the SCR catalyst and the DPF-SCR.