Bypass controlled regeneration of NOx adsorbers

Abstract

In a method and apparatus for regenerating a lean NOx adsorber, the NOx adsorber treats exhaust gases created during the combustion of gaseous fuels in general. A bypass line maintains a target regeneration flow of exhaust gas through the NOx adsorber during regeneration regardless of operating demands on the engine. Closed-loop and open-loop control are employed. The closed-loop control employs sensors that determine properties of the exhaust gas during regeneration, and the controller uses those properties to provide an efficient regeneration cycle. A regeneration map is also provided that uses creation of in-cylinder regeneration conditions for the exhaust gas in combination with in-line regeneration conditions for the exhaust gas.

1 . A method of regenerating a lean NOx adsorber, said lean NOx adsorber used to remove NOx from exhaust gas generated by combustion of a fuel in a combustion chamber of an operating internal combustion engine, said method comprising: 
 (a) determining a target regeneration flow of said exhaust gas through said lean NOx adsorber;    (b) directing a regeneration flow of said exhaust gas through said lean NOx adsorber, said regeneration flow established by one of: 
 bypassing a bypass flow of said exhaust gas around said lean NOx adsorber when said target regeneration flow is less than exhaust gas flow from said engine, resulting in said regeneration flow being substantially the same as said target regeneration flow, and  
 directing substantially all of said exhaust gas through said lean NOx adsorber when said target regeneration flow is greater than said exhaust gas flow from said engine, said exhaust gas flow from said engine and said bypass flow established by reference to at least one of:  
 (1) engine speed,  
 (2) engine load,  
 (3) engine intake manifold temperature,  
 (4) intake air mass flow,  
 (5) engine inlet fuel flow,  
 (6) engine intake manifold pressure,  
 (7) measured engine exhaust gas flow,  
 (8) exhaust gas temperature, and  
 (9) exhaust gas pressure;  
   (c) reacting, within said exhaust gas and upstream of said lean NOx adsorber, a reductant to maintain a lambda of said regeneration flow of less than 1 across said lean NOx adsorber.    
   
   
       2 . The method of  claim 1  wherein said target regeneration flow is determined based, at least in part, on an NOx concentration in said exhaust gas.  
   
   
       3 . The method of  claim 1  wherein said reductant is hydrogen.  
   
   
       4 . The method of  claim 1  wherein said reductant is a hydrocarbon.  
   
   
       5 . The method of  claim 4  wherein said hydrocarbon comprises methane.  
   
   
       6 . The method of  claim 5  further comprising introducing hydrogen into said regeneration flow by reforming said methane within said exhaust gas upstream of said lean NOx adsorber.  
   
   
       7 . The method of  claim 1  wherein said fuel and said reductant are interchangeable.  
   
   
       8 . The method of  claim 1  wherein said bypass flow is directed through a second lean NOx adsorber.  
   
   
       9 . A method of operating an internal combustion engine equipped with an aftertreatment system for removing NOx from exhaust gas generated by combustion of a fuel in at least one combustion chamber of said engine, said method comprising: 
 during normal operation of said engine, directing all of said exhaust gas through a lean NOx adsorber;    periodically regenerating said lean NOx adsorber by a regeneration cycle defined by a regeneration cycle start time and a regeneration cycle end time, during said regeneration cycle:    (a) determining a target regeneration flow of said exhaust gas through said lean NOx adsorber,    (b) directing a regeneration flow of said exhaust gas through said lean NOx adsorber, said regeneration flow established by one of: 
 bypassing a bypass flow of said exhaust gas around said lean NOx adsorber when said target regeneration flow is less than exhaust gas flow from said engine, resulting in said regeneration flow being substantially the same as said target regeneration flow, and  
 directing substantially all of said exhaust gas through said lean NOx adsorber when said target regeneration flow is greater than said exhaust gas flow from said engine, said exhaust gas flow from said engine and said bypass flow determined by reference to at least one of:  
 (1) engine speed,  
 (2) engine load,  
 (3) engine intake manifold temperature,  
 (4) intake air mass flow,  
 (5) engine inlet fuel flow,  
 (6) engine intake manifold pressure,  
 (7) measured engine exhaust gas flow,  
 (8) exhaust gas temperature,  
 (9) exhaust gas pressure;  
   (c) reacting, within the exhaust gas and upstream of the lean NOx adsorber, a reductant to maintain a lambda of said regeneration flow of less than 1 across the lean NOx adsorber.    
   
   
       10 . The method of  claim 9  wherein said reductant is hydrogen.  
   
   
       11 . The method of  claim 9  wherein said reductant is a hydrocarbon.  
   
   
       12 . The method of  claim 11  wherein said hydrocarbon comprises methane.  
   
   
       13 . The method of  claim 12  further comprising introducing hydrogen into said regeneration flow by reforming said methane within said exhaust gas upstream of said lean NOx adsorber.  
   
   
       14 . The method of  claim 9  wherein said fuel and said reductant are interchangeable.  
   
   
       15 . The method of  claim 12  wherein reacting of said hydrocarbon occurs within said exhaust gas prior to directing said bypass flow around said lean NOx adsorber.  
   
   
       16 . The method of  claim 12  wherein reacting of said hydrocarbon occurs within said regeneration flow.  
   
   
       17 . The method of  claim 12  wherein said hydrocarbon is directed into said exhaust gas by at least one of a valve and an injector.  
   
   
       18 . The method of  claim 9  wherein said regeneration cycle end time is determined when said lambda of said regeneration flow downstream of said lean NOx adsorber is below a pre-determined threshold concentration.  
   
   
       19 . The method of  claim 9  wherein said regeneration cycle end time is determined when a concentration of said reductant downstream of said lean NOx adsorber is above a pre-determined threshold concentration.  
   
   
       20 . The method of  claim 13  wherein said regeneration cycle end time is determined when a concentration of at least one of CO or H 2  downstream of said lean NOx adsorber is above a pre-determined threshold concentration.  
   
   
       21 . The method of  claim 9  wherein said regeneration flow is controlled by at least one valve.  
   
   
       22 . The method of  claim 9  wherein said regeneration flow is controlled by a bypass valve in a bypass line and an exhaust valve in an exhaust line.  
   
   
       23 . The method of  claim 22  wherein said bypass valve is a variable control valve.  
   
   
       24 . The method of  claim 23  wherein said exhaust valve is a variable control valve.  
   
   
       25 . The method of  claim 9  wherein said regeneration cycle start time is determined when a NOx concentration within said exhaust gas downstream of said lean NOx adsorber is in excess of a threshold concentration as compared to a NOx concentration out of said engine.  
   
   
       26 . The method of  claim 12  further comprising, when operating said engine in a predefined low load, low speed mode, wherein said lambda of said exhaust gas is less than one as a result of combustion of said fuel within said combustion chamber.  
   
   
       27 . The method of  claim 26  wherein said engine is a direct injection engine.  
   
   
       28 . The method of  claim 9  further comprising during said regeneration cycle directing said exhaust gas downstream of said lean NOx adsorber through a clean-up catalyst.  
   
   
       29 . The method of  claim 28  wherein said clean-up catalyst removes NOx from said exhaust gas.  
   
   
       30 . The method of  claim 28  wherein said clean-up catalyst removes reductant from said exhaust gas.  
   
   
       31 . The method of  claim 28  wherein said clean-up catalyst removes hydrogen sulfide from said exhaust gas.  
   
   
       32 . The method of  claim 9  further comprising directing said exhaust gas through a particulate filter upstream of said lean NOx adsorber.  
   
   
       33 . The method of  claim 9  wherein said bypass flow is directed through a second lean NOx adsorber.  
   
   
       34 . A method of operating a lean burn internal combustion engine equipped with an aftertreatment system for removing NOx from exhaust gas generated by combustion of a fuel in at least one combustion chamber of said engine, said method comprising: 
 (a) during normal operation of said engine, directing all of said exhaust gas, which results from combustion of a lean fuel mixture, through a lean NOx adsorber;    (b) periodically regenerating said lean NOx adsorber using a predetermined regeneration strategy selected from one of a high load strategy, a midrange load strategy and a low load strategy, said regeneration strategy causing said exhaust gas pass through said lean NOx adsorber: 
 during said high load strategy: reacting, upstream of said lean NOx adsorber, a reductant to maintain a lambda of said exhaust gas of less than 1 across said NOx adsorber,  
 during said low load strategy: transitioning from lean burn in said normal operation to rich burn of said fuel in said combustion chamber to generate said exhaust gas wherein said lambda of said exhaust gas is less than 1;  
 transitioning from lean burn in said normal operation to rich burn of said fuel, with said combustion chamber in a rich environment, to generate said exhaust gas wherein said lambda is less than 1, and reacting, upstream of said lean NOx adsorber, a reductant.  
   
   
   
       35 . An aftertreatment system for removing NOx from exhaust gas produced during combustion of a fuel within a combustion chamber of an operating internal combustion engine, said aftertreatment system comprising: 
 (a) an exhaust line for directing said exhaust gas from said engine,    (b) a lean NOx adsorber disposed in said exhaust line for removing said NOx,    (c) a regeneration catalyst disposed in said exhaust line upstream of said lean NOx adsorber, said catalyst capable of promoting oxidizing or reforming of a reductant,    (d) a reductant line for delivering said reductant from a reductant store to said exhaust line upstream of said catalyst,    (e) a reductant flow control disposed in said reductant line for controlling flow of said reductant into said exhaust line,    (f) a bypass line for directing said exhaust gas around said lean NOx adsorber,    (g) a second lean NOx adsorber,    (h) at least one bypass flow control capable of controlling flow of said exhaust gas through said bypass line,    (i) a controller,    (j) at least one sensor providing control information to said controller, said controller capable of adjusting said at least one valve in response to said control information.    
   
   
       36 . The aftertreatment system of  claim 35  wherein said reductant is hydrogen.  
   
   
       37 . The aftertreatment system of  claim 35  wherein said reductant is a gaseous hydrocarbon, said catalyst capable of reducing said gaseous hydrocarbon to provide hydrogen with said exhaust gas.  
   
   
       38 . The aftertreatment system of  claim 35  wherein said catalyst is a reformer in series with an oxidation catalyst.  
   
   
       39 . The aftertreatment system of  claim 35  wherein said catalyst is a oxidation catalyst.  
   
   
       40 . The aftertreatment system of  claim 35  wherein said catalyst comprises an oxidation catalyst combined with a reformer.  
   
   
       41 . The aftertreatment system of  claim 35  further comprising a second close coupled catalyst proximate to said engine for oxidizing said reductant when said exhaust gas proximate to said regeneration catalyst is at a temperature below a predetermined threshold temperature, said predetermined threshold temperature below which said catalyst is unable to efficiently promote reaction of said reductant.  
   
   
       42 . The aftertreatment system of  claim 35  further comprising an injector for injecting said reductant into said exhaust line.  
   
   
       43 . The aftertreatment system of  claim 35  wherein said by-pass flow control is a valve.  
   
   
       44 . The aftertreatment system of  claim 35  wherein said reductant store is a fuel system of said engine.  
   
   
       45 . The aftertreatment system of  claim 35  further comprising a particulate filter disposed in said exhaust line downstream of and proximate to said regeneration catalyst.  
   
   
       46 . The aftertreatment system of  claim 35  further comprising a second lean NOx adsorber in said bypass line.  
   
   
       47 . The aftertreatment system of  claim 46  further comprising a second regeneration catalyst disposed in said bypass line upstream of said second lean NOx adsorber.  
   
   
       48 . The aftertreatment system of  claim 35  further comprising a clean-up catalyst disposed downstream of said lean NOx adsorber, said clean-up catalyst capable of removing, from said exhaust gas, at least one of: 
 (a) said NOx,    (b) said reductant, and    (c) hydrogen sulfide.