Apparatus comprising lean burn ic engine and an exhaust system therefor

Abstract

An apparatus comprises: (i) a lean burn internal combustion engine; (ii) an exhaust system for treating a flowing exhaust gas from the engine, which system comprising: (a) a first substrate monolith comprising a NOx adsorber catalyst (NAC); and (b) a catalysed soot filter (CSF) comprising a filter substrate; and (iii) means for enriching the exhaust gas to provide an enriched exhaust gas composition intermittently during normal lean running operation for removing sulfate adsorbed on the NAC, wherein the exhaust system comprises: (c) a compound located downstream of at least some of the NAC, which compound is effective to remove and/or convert at least some hydrogen sulfide in enriched exhaust gas derived from removing sulfate adsorbed on the NAC.

1 . An apparatus comprising:
 (i) a lean burn internal combustion engine;   (ii) an exhaust system for treating a flowing exhaust gas from the engine, which system comprising:
 (a) a first substrate monolith comprising a NO x  adsorber catalyst (NAC); and 
 (b) a catalysed soot filter (CSF) comprising a filter substrate; and 
   (iii) means for enriching the exhaust gas to provide an enriched exhaust gas composition intermittently during normal lean running operation for removing sulfate adsorbed on the NAC, wherein the exhaust system comprises:
 (c) a compound located downstream of at least some of the NAC, which compound is effective to remove and/or convert at least some hydrogen sulfide in enriched exhaust gas derived from removing sulfate adsorbed on the NAC. 
   
     
     
         2 . An apparatus according to  claim 1 , wherein the filter substrate is located upstream of the first substrate monolith. 
     
     
         3 . An apparatus according to  claim 2 , wherein the first substrate monolith comprises the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         4 . An apparatus according to  claim 3 , wherein the first substrate monolith has a length extending between an inlet end and an outlet end thereof, wherein the NAC is located in a first zone of substantially uniform length defined at an upstream end by the inlet end of the first substrate monolith and at a downstream end by a point more than one half way along the first substrate monolith measured from the inlet end and the compound effective to remove and/or convert at least some hydrogen sulfide is located in a second zone of substantially uniform length defined at an upstream end by a point more than one half way along the first substrate monolith length measured from the inlet end and at a downstream end by the outlet end of the first substrate monolith. 
     
     
         5 . An apparatus according to  claim 2 , further comprising a second substrate monolith located downstream of the first substrate monolith, wherein the second substrate monolith comprises the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         6 . An apparatus according to  claim 1 , wherein the first substrate monolith is the filter substrate. 
     
     
         7 . An apparatus according to  claim 6 , wherein the filter substrate comprises both the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         8 . An apparatus according to  claim 7 , wherein the filter substrate has a length extending from an inlet end to an outlet end thereof, wherein the NAC is located in a third zone of substantially uniform length defined at an upstream end by the inlet end of the filter substrate and at a downstream end by a point more than one half way along the filter substrate measured from the inlet end and wherein the compound effective to remove and/or convert at least some hydrogen sulfide is located in a fourth zone of substantially uniform length defined at an upstream end by a point more than one half way along the filter substrate length measured from the inlet end and defined at a downstream end by the outlet end of the filter substrate itself. 
     
     
         9 . An apparatus according to  claim 6 , further comprising a second substrate monolith located downstream of the filter substrate, wherein the second substrate monolith comprises the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         10 . An apparatus according to  claim 1 , wherein the filter substrate has an inlet end and an outlet end, and wherein the inlet end of the filter substrate is located downstream of the first substrate monolith in a flow direction of the exhaust gas. 
     
     
         11 . An apparatus according to  claim 10 , wherein the compound effective to remove and/or convert at least some hydrogen sulfide is located on a third substrate monolith disposed between the first substrate monolith and the filter substrate. 
     
     
         12 . An apparatus according to  claim 10 , wherein the first substrate monolith comprises the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         13 . An apparatus according to  claim 12 , wherein the first substrate monolith has a length extending between an inlet end and an outlet end thereof, wherein the NAC is located in a first zone of substantially uniform length defined at an upstream end by the inlet end of the first substrate monolith and at a downstream end by a point more than one half way along the first substrate monolith length measured from the inlet end and the compound effective to remove and/or convert at least some hydrogen sulfide is located in a second zone of substantially uniform length defined at an upstream end by a point more than one half way along the first substrate monolith length measured from the inlet end and at a downstream end by the outlet end of the first substrate monolith. 
     
     
         14 . An apparatus according to  claim 10 , wherein the filter substrate comprises the compound effective to remove and/or convert at least some hydrogen sulfide. 
     
     
         15 . An apparatus according to  claim 14 , wherein the filter substrate has a length extending from an inlet end to an outlet end thereof, wherein the compound effective to remove and/or convert at least some hydrogen sulfide is located in a fifth zone of substantially uniform length defined at an upstream end by the inlet end itself and at a downstream end by a point up to one half way along the filter substrate length measured from the inlet end. 
     
     
         16 . An apparatus according to  claim 10 , further comprising a fourth substrate monolith, wherein the fourth substrate monolith comprises the compound effective to remove and/or convert at least some hydrogen sulfide disposed downstream of the filter substrate. 
     
     
         17 . An apparatus according to  claim 1 , wherein the compound effective to remove and/or convert at least some hydrogen sulfide is located at one of the following positions in the exhaust system:
 (1) between the NAC and the filter substrate;   (2) on the first substrate downstream of the NAC;   (3) on the filter substrate;   (4) between the filter substrate and an exhaust system exit to atmosphere;   (5) at both positions (1) and (2);   (6) at both positions (2) and (3);   (7) at both positions (1) and (3); and   (8) at all of positions (1), (2) and (3).   
     
     
         18 . An apparatus according to  claim 1 , wherein the exhaust system comprises an oxidation catalyst disposed between the engine and the NAC. 
     
     
         19 . An apparatus according to  claim 18 , wherein the oxidation catalyst is located on a fifth substrate monolith disposed between the engine and the first substrate monolith or the filter substrate. 
     
     
         20 . An apparatus according to  claim 1 , wherein the first substrate monolith or the filter substrate comprises an oxidation catalyst located upstream of the NAC. 
     
     
         21 . An apparatus according to  claim 20 , wherein the first substrate monolith or the filter substrate has a length extending between an inlet end and an outlet end thereof and the oxidation catalyst is located in a sixth zone of substantially uniform length defined at an upstream end by the inlet end of the first substrate monolith or filter substrate and at a downstream end by a point less than one half way along the first substrate monolith length measured from the inlet end. 
     
     
         22 . An apparatus according to  claim 21 , wherein:
 (a) the filter substrate is located upstream of the first substrate monolith;   (b) the first substrate monolith comprises the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide; and   (c) the compound effective to remove and/or convert at least some hydrogen sulfide is located in a seventh zone of substantially uniform length defined at an upstream end by a point more than one half way along the first substrate monolith length or the filter substrate length measured from the inlet end and defined at a downstream end by the outlet end of the first substrate monolith or the filter substrate itself.   
     
     
         23 . An apparatus according to  claim 1 , wherein the means for enriching the exhaust gas is selected from the group consisting of:
 (a) an engine management unit configured intermittently to cause the engine to emit an enriched exhaust gas;   (b) an injector for injecting a reductant into a flowing exhaust gas carried by the exhaust system downstream of the engine; and   (c) a reforming catalyst for generating a gas mixture comprising H 2  and CO from exhaust gas and diesel fuel.   
     
     
         24 . An apparatus according to  claim 1 , wherein the hydrogen sulfide removing and/or converting compound is selected from the group consisting of NiO, CaO, Fe 2 O 3  and BaO. 
     
     
         25 . An apparatus according to  claim 1 , wherein the enriching means comprises means for controlling a temperature of the NAC during enrichment to remove and/or convert sulfate from the NAC. 
     
     
         26 . An apparatus according to  claim 25 , wherein the enriching means provides a net rich exhaust gas composition (lambda<1) and wherein the temperature controlling means comprises means for intermittently adjusting the exhaust gas composition to the lean side (lambda>1) during exhaust gas enrichment to remove and/or convert sulfate adsorbed on the NAC. 
     
     
         27 . An apparatus according to  claim 26 , wherein the means for intermittently adjusting the exhaust gas composition to the lean side (lambda>1) controls one or both of: an engine air-to-fuel ratio; and an injector for injecting air into exhaust gas downstream of the engine. 
     
     
         28 . An apparatus according to  claim 1 , wherein the enriching means comprises a microprocessor (ECU). 
     
     
         29 . An apparatus according to  claim 1 , wherein the lean burn internal combustion engine is a diesel engine. 
     
     
         30 . A vehicle comprising an apparatus according to  claim 1 . 
     
     
         31 . A method of desulfating a NO x  adsorber catalyst (NAC) in an exhaust system of a lean burn internal combustion engine comprising a first substrate monolith comprising a NO adsorber catalyst (NAC); and a catalysed soot filter (CSF) comprising a filter substrate, which method comprising the steps of:
 (i) contacting sulfated NAC with enriched exhaust gas for a time and at a temperature sufficient to desorb sulfur-containing species adsorbed thereon, thereby to generate hydrogen sulfide; and   (ii) contacting exhaust gas containing hydrogen sulfide with a compound effective to remove and/or convert at least some hydrogen sulfide from the rich exhaust gas,   
       wherein at least some of the compound effective to remove and/or convert at least some hydrogen sulfide from the exhaust gas is disposed downstream of the NAC. 
     
     
         32 . A method according to  claim 31 , comprising the step of releasing sulfur dioxide from the compound effective to remove and/or convert at least some hydrogen sulfide from the enriched exhaust gas by intermittently contacting said compound with a leaner exhaust gas during step (i). 
     
     
         33 . An apparatus according to  claim 21 , wherein:
 (a) the first substrate monolith is the filter substrate;   (b) the filter substrate comprises both the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide; and   (c) the compound effective to remove and/or convert at least some hydrogen sulfide is located in a seventh zone of substantially uniform length defined at an upstream end by a point more than one half way along the first substrate monolith length or the filter substrate length measured from the inlet end and defined at a downstream end by the outlet end of the first substrate monolith or the filter substrate itself.   
     
     
         34 . An apparatus according to  claim 21 , wherein:
 (a) the filter substrate has an inlet end and an outlet end, and wherein the inlet end of the filter substrate is located downstream of the first substrate monolith in a flow direction of the exhaust gas;   (b) the first substrate monolith comprises the NAC and the compound effective to remove and/or convert at least some hydrogen sulfide; and   (c) the compound effective to remove and/or convert at least some hydrogen sulfide is located in a seventh zone of substantially uniform length defined at an upstream end by a point more than one half way along the first substrate monolith length or the filter substrate length measured from the inlet end and defined at a downstream end by the outlet end of the first substrate monolith or the filter substrate itself.   
     
     
         35 . An apparatus according to  claim 29 , wherein the diesel engine is a heavy duty diesel engine.