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  Management of thermal fluctuations in lean nox adsorber aftertreatment systemsRelated Patent Categories: Power Plants, Internal Combustion Engine With Treatment Or Handling Of Exhaust Gas, By Means Producing A Chemical Reaction Of A Component Of The Exhaust Gas, Condition Responsive Control Of Heater, Cooler, Igniter, Or Fuel Supply Of ReactorManagement of thermal fluctuations in lean nox adsorber aftertreatment systems description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060053776, Management of thermal fluctuations in lean nox adsorber aftertreatment systems. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION(S) [0001] This application is a continuation of International Application No. PCT/CA2004/000390, having an international filing date of Mar. 11, 2004, entitled "Management of Thermal Fluctuations in Lean NO.sub.x Adsorber Aftertreatment Systems". International Application No. PCT/CA2004/000390 claimed priority benefits, in turn, from Canadian Patent Application No. 2,422,164 filed Mar. 14, 2003 and from Canadian Patent Application No. 2,453,689 filed Dec. 17, 2003. International Application No. PCT/CA2004/000390 is hereby incorporated by reference herein in its entirety. FIELD OF THE INVENTION [0002] This invention relates to methods and apparatuses for managing exhaust gas heat over the range of operating conditions required by a lean NOx adsorber aftertreatment system. BACKGROUND OF THE INVENTION [0003] Emissions controls for internal combustion engines are becoming increasingly important in transportation and energy applications. Oxides of nitrogen (NOx) are of particular concern. NOx forms during combustion in internal combustion engines. [0004] A lean NOx adsorber (LNA) can be employed to remove NOx from exhaust gas. LNAs reduce NOx by trapping the NOx in a catalyst washcoat. NOx trapping in the LNA is referred to herein as adsorption. The NOx stored in the washcoat is reduced to nitrogen gas (N.sub.2) periodically. This reduction process is referred to as regeneration or a regeneration cycle. [0005] Where sulfur is found in the engine fuel or where sulfur-containing engine lubricating oil has leaked into the combustion chamber, oxides of sulfur can also be trapped within the LNA washcoat. As discussed in, by way of example, U.S. Pat. No. 6,393,834, sulfur poisoning of LNAs from oxides of sulfur in the exhaust gas can interfere with the ability of the LNA to remove NOx. Removing these oxides of sulfur periodically during operation of the engine helps to maintain the efficiency of the LNA. Processes employed to remove sulfur compounds are referred to as de-sulfation. Regeneration and de-sulfation cycles both require a low oxygen potential (or "rich") environment to be effective. Regeneration, de-sulfation and removal of NOx each work best when the exhaust gas temperature is within a different range. [0006] The acid-based chemistry of the washcoat dictates the temperature ranges at which the LNA washcoat effectively traps NOx and SOx. In general, trapped sulfate compounds are more stable than trapped nitrate compounds. That is, the ability of the LNA washcoat to store sulfates extends to higher temperature ranges than is the case for NOx. For similar reasons, the temperature at which de-sulfation proceeds tends to be higher than the temperature required for regeneration. [0007] "De-sulfation temperature" is used herein to refer to that relatively high temperature at which sulfur is effectively released from the LNA washcoat. The performance of current LNA washcoats tends to deteriorate, mainly due to sintering, when exposed to temperatures in excess of 700.degree. C. Exceeding 700.degree. C. by a significant margin increases the rate of deterioration. De-sulfation temperatures can approach and exceed 700.degree. C. leading to poor long-term performance of the LNA. [0008] For regeneration of the LNA, a regeneration temperature which is less than the de-sulfation temperature is generally preferred. [0009] During the adsorption phase, the exhaust gas is lean and NOx is being trapped within the LNA. Lower exhaust gas temperatures can be tolerated during the adsorption phase and are selected to allow the LNA to adsorb NOx over a suitable range of the engine map. Preferred exhaust gas temperatures during an adsorption cycle can overlap with regeneration temperatures and are generally lower than de-sulfation temperatures (all of which can depend on the washcoat composition, the reductant chosen and other factors within the aftertreatment system). [0010] In light of the range of preferred exhaust gas temperatures that depend on the aftertreatment control sought for the LNA, flexibility in providing those temperatures over the range of potential engine operating conditions is important. Control over the temperature to which the LNA is exposed can both extend the life of the LNA and improve its effectiveness at removing NOx from internal combustion engine exhaust gas. Moreover, the faster the regeneration or de-sulfation temperatures are reached within the exhaust gas and then returned to preferred adsorption cycle temperatures, the less the fuel penalty for regeneration or de-sulfation and the less NOx delivered from the engine as a result of these cycles. [0011] Oxidation of a reductant in the exhaust gas, referred to here as in-line oxidation, can provide the heat and reductants to either regenerate or de-sulfate an LNA as well as create the reduced oxygen potential environment for de-sulfation. Oxidation can be promoted by a catalyst. The catalyst should be located in close enough proximity to the engine that exhaust gas temperatures are sufficient to cause the catalyst to "light-off" at engine out temperatures yet still be proximate enough to the LNA to provide rich exhaust gas regeneration temperatures or de-sulfation temperatures. However, the LNA reactive capacity (the ability of the LNA to trap NOx) is relatively low at the temperature needed for the effective operation of the reformer/oxidation catalyst. Therefore, consideration should be given to ensure that exhaust gas passing through the LNA during an adsorption cycle is cool enough (for example, placed distant from the engine) to allow the LNA to operate efficiently over a wide range of engine operating conditions. [0012] All references to "upstream" and "downstream" herein describe the relative position of components of the aftertreatment in relation to the direction of the flow of exhaust gas during an adsorption cycle of the LNA aftertreatment system (which may not be the same as the flow during a regeneration cycle or de-sulfation cycle), unless otherwise stated. [0013] The present technique provides methods and apparatuses for managing exhaust gas temperature using an LNA over a wide range of engine operating conditions. SUMMARY OF THE INVENTION [0014] This present technique manages exhaust gas heat into an LNA during adsorption, de-sulfation and regeneration cycles of the LNA. One aspect of the present technique provides a hot route that shortcuts or provides a bypass route around, a cooling path between the LNA and an oxidation catalyst. Another aspect of the present technique provides a long route or cooling route through the aftertreatment system. The coding route allows the exhaust gas to cool where needed. Another aspect provides a cooling route with a heat exchanger between an oxidation catalyst and an LNA for cooling the exhaust gas as needed. Another aspect of the present technique provides a cooling route with a turbine between an oxidation catalyst and a LNA for cooling the exhaust and extracting energy from the exhaust gas heat. This energy can be employed, in another aspect of the present technique, to introduce air into the exhaust gas stream to cool the exhaust (by dilution) when needed. Another aspect of the present technique provides for a sulfur trap to manage sulfur in the aftertreatment system. [0015] An aftertreatment system treats NOx found in exhaust gas produced during combustion of a fuel within a combustion chamber of an operating internal combustion engine. The system comprises: [0016] an exhaust line for directing the exhaust gas from the engine; [0017] a lean NOx adsorber disposed in the exhaust line; [0018] a first catalyst disposed in the exhaust line upstream of the LNA, the catalyst capable of oxidizing a reductant in the exhaust gas; [0019] a reductant line for delivering a reductant from a reductant store to the catalyst; [0020] a reductant flow control disposed in the reductant line for controlling flow of the reductant into the exhaust line; and [0021] a flow control for controlling flow of exhaust gas through the hot line and the cooling line. The exhaust line is capable of delivering exhaust gas from the first catalyst to the lean NOx adsorber. [0022] In one embodiment of the aftertreatment system, the cooling line and the hot line are placed between the catalyst and the NOx adsorber. The cooling line is preferably longer than the exhaust line. [0023] The system can further comprise a turbine, disposed within the cooling line, which drives an air blower disposed in an air dilution line for compressing and directing air into the cooling line. [0024] In one embodiment of the system, an air blower disposed in an air dilution line can compress and direct air into the cooling line. A heat exchanger can also be disposed in the cooling line. [0025] The aftertreatment system can further comprise a close-coupled catalyst in the exhaust line upstream of the system's first catalyst. The reductant line delivers reductant to the exhaust line, upstream of the close-coupled catalyst. In another embodiment, the reductant line delivers reductant upstream of the first catalyst. [0026] In a further embodiment of the system, the exhaust line can comprise a bypass line employed to direct exhaust gas around the first catalyst. Continue reading about Management of thermal fluctuations in lean nox adsorber aftertreatment systems... 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