Exhaust aftertreatment system with low-temperature scr

Abstract

An aftertreatment system may treat exhaust gas discharged from an engine. The system may include first and second selective-catalytic-reduction (SCR) catalysts and a valve. The valve may be disposed upstream of the first SCR catalyst and at least one of an oxidation catalyst and a particulate filter. The valve is connected to first and second exhaust flow paths and is movable between a first position allowing exhaust gas to flow through the first flow path and bypass the second flow path and a second position allowing exhaust gas to flow through the second flow path and bypass the first flow path. The second SCR catalyst may be a low-temperature SCR catalyst and may be disposed in the second flow path. A control module may cause the valve to move between the first and second positions based on a temperature of the exhaust gas and/or a temperature of the engine.

1 . An aftertreatment system for treating exhaust gas discharged from a combustion engine, the aftertreatment system comprising:
 at least one of an oxidation catalyst and a particulate filter configured to receive exhaust gas;   first and second selective-catalytic-reduction catalysts;   a valve disposed upstream of the first selective-catalytic-reduction catalyst and the at least one of the oxidation catalyst and particulate filter, the valve connected to first and second exhaust flow paths and movable between a first position allowing exhaust gas to flow through the first exhaust flow path and bypass the second exhaust flow path and a second position allowing exhaust gas to flow through the second exhaust flow path and bypass the first exhaust flow path, the second selective-catalytic-reduction catalyst is a low-temperature selective-catalytic-reduction catalyst and is disposed in the second exhaust flow path; and   a control module in communication with the valve and configured to cause the valve to move between the first and second positions based on an operating parameter of the combustion engine.   
     
     
         2 . The aftertreatment system of  claim 1 , wherein the first and second exhaust flow paths are disposed upstream of the at least one of the oxidation catalyst and particulate filter. 
     
     
         3 . The aftertreatment system of  claim 2 , wherein the first and second exhaust flow paths are disposed upstream of the first selective-catalytic-reduction catalyst. 
     
     
         4 . The aftertreatment system of  claim 1 , wherein the second exhaust flow path includes a fluid injection port disposed upstream of the second selective-catalytic-reduction catalyst. 
     
     
         5 . The aftertreatment system of  claim 4 , further comprising another fluid injection port disposed between the first selective-catalytic-reduction catalyst and the at least one of the oxidation catalyst and the particulate filter. 
     
     
         6 . The aftertreatment system of  claim 1 , wherein the at least one of the oxidation catalyst and particulate filter is disposed in the first exhaust flow path. 
     
     
         7 . The aftertreatment system of  claim 6 , wherein the first selective-catalytic-reduction catalyst is disposed in the first exhaust flow path. 
     
     
         8 . An aftertreatment system for treating exhaust gas discharged from a combustion engine, the aftertreatment system comprising:
 a first injection port through which reagent is injected into an exhaust stream;   a first selective-catalytic-reduction catalyst disposed downstream of the first injection port, the first selective-catalytic-reduction catalyst is a low-temperature selective-catalytic-reduction catalyst;   at least one of an oxidation catalyst and a particulate filter disposed downstream of the low-temperature selective-catalytic-reduction catalyst;   a second injection port through which reagent is injected into the exhaust stream downstream of the at least one of the oxidation catalyst and particulate filter; and   a second selective-catalytic-reduction catalyst disposed downstream of the second injection port.   
     
     
         9 . The aftertreatment system of  claim 8 , further comprising:
 a low-temperature flow path including the first selective-catalytic-reduction catalyst;   a bypass flow path isolated from the first selective-catalytic-reduction catalyst; and   a valve disposed upstream of the second selective-catalytic-reduction catalyst and movable between a first position allowing exhaust gas to flow through the low-temperature flow path and preventing exhaust gas from flowing through the bypass flow path and a second position allowing exhaust gas to flow through the bypass flow path and preventing exhaust gas from flowing through the low-temperature flow path.   
     
     
         10 . The aftertreatment system of  claim 9 , wherein the first injection port provides reagent to the low-temperature flow path. 
     
     
         11 . The aftertreatment system of  claim 10 , wherein the low-temperature flow path and the bypass flow path are disposed upstream of the at least one of the oxidation catalyst and particulate filter. 
     
     
         12 . The aftertreatment system of  claim 9 , further comprising a control module in communication with the valve and configured to cause the valve to move between the first and second positions based on an operating parameter of the combustion engine. 
     
     
         13 . The aftertreatment system of  claim 9 , wherein the bypass flow path includes the second selective-catalytic-reduction catalyst. 
     
     
         14 . The aftertreatment system of  claim 13 , wherein the bypass flow path includes the second injection port. 
     
     
         15 . An aftertreatment system for treating exhaust gas discharged from a combustion engine, the aftertreatment system comprising:
 a low-temperature flow path including a first selective-catalytic-reduction catalyst;   a bypass flow path including a second selective-catalytic-reduction catalyst, the bypass flow path isolated from the first selective-catalytic-reduction catalyst; and   a valve configured to receive exhaust gas from the combustion engine and movable between a first position allowing exhaust gas to flow through the low-temperature flow path and preventing exhaust gas from flowing through the bypass flow path and a second position allowing exhaust gas to flow through the bypass flow path and preventing exhaust gas from flowing through the low-temperature flow path.   
     
     
         16 . The aftertreatment system of  claim 15 , further comprising a control module in communication with the valve and configured to cause the valve to move between the first and second positions based on an operating parameter of the combustion engine. 
     
     
         17 . The aftertreatment system of  claim 15 , further comprising an oxidation catalyst and a particulate filter disposed upstream of the second selective-catalytic-reduction catalyst. 
     
     
         18 . The aftertreatment system of  claim 17 , wherein the oxidation catalyst and the particulate filter are disposed upstream of the valve. 
     
     
         19 . The aftertreatment system of  claim 18 , further comprising another valve disposed upstream of the oxidation catalyst and the particulate filter and movable between a first position allowing exhaust gas to flow through the oxidation catalyst and the particulate filter and a second position allowing exhaust gas to flow through another flow path that is isolated from the oxidation catalyst and the particulate filter. 
     
     
         20 . The aftertreatment system of  claim 15 , further comprising an ammonia gas generator disposed upstream of at least one of the first and second selective-catalytic-reduction catalysts. 
     
     
         21 . An aftertreatment system for treating exhaust gas discharged from a combustion engine, the aftertreatment system comprising:
 a first selective-catalytic-reduction catalyst;   a second selective-catalytic-reduction catalyst in fluid communication with the first selective-catalytic-reduction catalyst;   a control valve in communication with the first and second selective-catalytic-reduction catalysts and movable between a first position causing exhaust gas to flow through the first selective-catalytic-reduction catalyst before flowing through the second selective-catalytic-reduction catalyst and a second position causing exhaust gas to flow through the second selective-catalytic-reduction catalyst before flowing through the first selective-catalytic-reduction catalyst.   
     
     
         22 . The aftertreatment system of  claim 21 , further comprising a control module in communication with the valve and configured to cause the control valve to move between the first and second positions based on an operating parameter of the combustion engine. 
     
     
         23 . The aftertreatment system of  claim 21 , further comprising an oxidation catalyst disposed upstream of the control valve. 
     
     
         24 . The aftertreatment system of  claim 21 , further comprising a particulate filter disposed upstream of the control valve. 
     
     
         25 . The aftertreatment system of  claim 21 , further comprising a downstream valve configured to receive exhaust gas after the exhaust gas has flowed through the first and second selective-catalytic-reduction catalysts. 
     
     
         26 . The aftertreatment system of  claim 25 , wherein the downstream valve is movable between a first position allowing exhaust gas from the second selective-catalytic-reduction catalyst to flow through the downstream valve and preventing exhaust gas from flowing from the downstream valve to the first selective-catalytic-reduction catalyst and a second position allowing exhaust gas from the first selective-catalytic-reduction catalyst to flow through the downstream valve and preventing exhaust gas from flowing from the downstream valve to the second selective-catalytic-reduction catalyst. 
     
     
         27 . The aftertreatment system of  claim 26 , further comprising a control module that moves the downstream valve into its first position and the control valve into its first position substantially simultaneously and moves the downstream valve into its second position and the control valve into its second position substantially simultaneously. 
     
     
         28 . The aftertreatment system of  claim 21 , further comprising an ammonia gas generator disposed upstream of at least one of the first and second selective-catalytic-reduction catalysts. 
     
     
         29 . An aftertreatment system for treating exhaust gas discharged from a combustion engine, the aftertreatment system comprising:
 a first exhaust gas flow path receiving a first portion of the exhaust gas from the combustion engine, the first exhaust gas flow path including an ammonia generator and an injection port through which a reagent is injected into the exhaust gas;   a second exhaust gas flow path receiving a second portion of the exhaust gas from the combustion engine and including at least one of a oxidation catalyst and a particulate filter;   a first selective-catalytic-reduction catalyst receiving exhaust gas from the first and second exhaust gas flow paths; and   a second selective-catalytic-reduction catalyst receiving exhaust gas from the first and second exhaust gas flow paths, the second selective-catalytic-reduction catalyst is a low-temperature selective-catalytic-reduction catalyst.   
     
     
         30 . The aftertreatment system of  claim 29 , wherein the second selective-catalytic-reduction catalyst is disposed downstream of the first selective-catalytic-reduction catalyst. 
     
     
         31 . The aftertreatment system of  claim 29 , wherein the first exhaust gas flow path includes an inlet disposed downstream of a turbocharger. 
     
     
         32 . The aftertreatment system of  claim 29 , wherein the first exhaust gas flow path includes an inlet disposed upstream of a turbocharger. 
     
     
         33 . The aftertreatment system of  claim 29 , wherein the injection port is disposed downstream of the ammonia generator. 
     
     
         34 . The aftertreatment system of  claim 1 , wherein the operating parameter is selected from the group consisting of: a temperature of the exhaust gas, a temperature of the combustion engine, a coolant temperature, and a runtime of the combustion engine. 
     
     
         35 . The aftertreatment system of  claim 12 , wherein the operating parameter is selected from the group consisting of: a temperature of the exhaust gas, a temperature of the combustion engine, a coolant temperature, and a runtime of the combustion engine. 
     
     
         36 . The aftertreatment system of  claim 16 , wherein the operating parameter is selected from the group consisting of: a temperature of the exhaust gas, a temperature of the combustion engine, a coolant temperature, and a runtime of the combustion engine. 
     
     
         37 . The aftertreatment system of  claim 22 , wherein the operating parameter is selected from the group consisting of: a temperature of the exhaust gas, a temperature of the combustion engine, a coolant temperature, and a runtime of the combustion engine.