CA2422188A1

CA2422188A1 - Bypass controlled regeneration of nox adsorbers

Info

Publication number: CA2422188A1
Application number: CA002422188A
Authority: CA
Inventors: Richard Ancimer; Olivier Lebastard; Jonathan M.S. Harris
Original assignee: Westport Research Inc
Current assignee: Westport Power Inc
Priority date: 2002-10-02
Filing date: 2003-03-14
Publication date: 2004-04-02
Also published as: EP1546517A2; CA2503602A1; AU2003271449A8; WO2004031546A3; WO2004031546A2; JP2006502345A; AU2003271449A1; US20050223699A1

Abstract

A method and apparatus for regenerating a NOx adsorber is disclosed where the NOx adsorber is used to treat exhaust gases created during the combustion of gaseous fuels in general. A bypass line is used to maintain a target regeneration flow of exhaust gas through the NOx adsorber during regeneration regardless of operating demands on the engine. A closed and open loop control is provided. The closed loop control using sensors determining properties of the exhaust gas during regeneration and the controller using those properties to provide an efficient regeneration cycle.

Description

_ 1 BYPASS CONTROhLED REGENERATION OF NOX ADSORBERS
Field of the Invention This invention relates to a method and apparatus fox regenerating a NOx absorber used in association with an internal combustion engine.
Backgrouzxd of the Invention Emissions controls for internal combustion engines are becoming increasingly important in transportation and energy applications. One class of pollutants of concern are oxides of nitrogen (NOx). NOx form: during combustion in internal combustion engines.
One effective NOx treatment system is a lean NOx adsorber (LNA). LNA systems need to be periodically regenerated. That is,:over time, a reluctant is needed to treat NOx traps to permit further NOx removal to'take place. It is desirable to provide an efficient means of regeneration.
As discussed in, by way of example, W0 00/76637, there are a variety of reductants available for NOx trap regeneration. By way of example, many hydrocarbons; carbon monoxide (CO) and hydrogen can be used as reductants. Hydrogen is especially effective as a reluctant: see US
5,953,911. Also, hydrogenis advantageous in regard to the emissions generated when hydrogen is used as a reluctant since the products are water and nitrogen. Other carbon-based reductants such as CO can also be useful, however, carbon-based reductants result in production of the greenhouse gas carbon dioxide.
Hydrogen is difficult to store and is generally not readily available. However, hydrocarbons are readily available since internal combustion engines typically use hydrocarbons as fuel: As hydrocarbons comprise hydrogen atoms, they provide a possible source of hydrogen. A
hydrocarbon fuel may be passed through a reformer to yield hydrogen.
Further, while hydrogen is an excellent reductant, any regeneration process that takes advantage of hydrogen runs the risk of expelling hydrogen with exhaust gas when regeneration is complete. This is undesirable due to the flammability of hydrogen. Also, regeneration using hydrogen from a hydrocarbon source consumes a potential fuel. Therefore, improving regeneration efficiency not only reduces expulsion of untreated NOx, it also helps to reduce consumption of hydrocarbons otherwise available as a fuel.
NOx emissions can also be reduced by managing combustion. NOx emissions can be reduced by using certain gaseous fuels in place of heavy hydrocarbons. Examples of such fuels include natural gas; methane and propane. Even with gaseous fuel, however, NOx emissions are not insignificant.
Developments in gaseous combustion processes have sought to: address NOx emissions problems.
Spark ignited gaseous fuel engines, wherein a premixed charge of air and gaseous fuel is ignited with a spark within. the combustion chamber, have resulteel in further reductions of NOx. Also, high pressure directly injected gaseous fuel, ignited by an ignition source such as a small quantity of relatively auto-ignitable pilot fuel introduced within the engine combustion chamber, yields an improvement over diesel-fuelled engines by reducing the emissions levels of NOx depending on the gaseous fuel chosen. However some NOx is still generated in such engines and therefore, it is desirable to reduce this pollutant.
This invention provides am efficient means,of regenerating a NOx adsorber.

Summary of the Invention The invention is directed to an efficient method and apparatus for regenerating a NOx adsorber. A method is disclosed providing a bypass strategy for regenerating a NOx adsorber efficiently.
A method is disclosed for regenerating a NOx adsorber efficiently by providing an easily recognizable marker indicating the completion of a regeneration cycle. This allows for real time monitoring of regeneration or a closed-loop regeneration method.
In a preferred method of regenerating a NOx adsorber that is. used-to remove NOx from exhaust gas generated by combustion of a fuel in a combustion chamber of an operating internal combustion engine, the method comprises:
(a) determining a target regeneration flow of the exhaust gas through the NOx adsorber, (b) directing a regeneration flow of the exhaust gas through the NOx adsorber, the regeneration flow established by one of either bypassing a bypass flow of the exhaust gas around the NOx adsorber when the target regeneration flow is less than the flow of the exhaust gas from the engine, resulting in the regeneration flow being substantially the same as the target regeneration flow, or directing substantially all of the exhaust gas through the NOx adsorber when the target regeneration flow is greater than the flow of the exhaust gas from he engine, the flow of the exhaust gas from he engine and the bypass flow determined by reference to at least one of:
the speed of the engine, 5 the load of the engine, the intake manifold temperature of the engine, the intake air mass flow, the fuel flow into the engine, the intake manifold pressure of the engine, and exhaust gas flow out of the engine, (c) directing a first quantity of a reductant into the exhaust line upstream of the NOx adsorber; and.
(d) oxidizing; within the exhaust gas and upstream of the NOx adsorber, the first quantity of the reluctant to maintain a lambda of the regeneration flow of less than one across the NOx adsorber.
The method can be practiced with the reluctant being hydrogen: The method can also be practiced with the reluctant being a hydrocarbon, and in a preferred example, the hydrocarbon is methane. A further aspect of the method can comprise reforming a second quantity of the hydrocarbon within the exhaust gas upstream of the NOx adsorber to introduce hydrogen into the regeneration flow.
In a preferred method the fuel that is burned in the engine is the same as the reluctant.
A method is also provided 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 the engine.
This method comprise directing all of the exhaust gas through a lean NOx adsorber during normal operation of the engine, and periodically regenerating the lean NOx adsorber during a regeneration cycle defined by a regeneration cycle start time and a regeneration cycle end time. The regeneration cycle includes:
(a) determining a target regeneration flow of the exhaust gas through the NOx adsorber, (b) directing a regeneration flow of the exhaust gas through the NOx adsorber, the regeneration flow established by one of either bypassing a bypass flow of the exhaust gas around the NOx adsorber when the target regeneration flow is less than the flaw of 'the exhaust gas from the engine, resulting in the regeneration flow being substantially the same as the target regeneration flow, and directing substantially all of the exhaust gas through the NOx adsorber when the target regeneration flow is'greater than the flow of the exhaust gas from the engine; the flow of the exhaust gas from he engine and the bypass flow determined by reference to at least one of:
the speed of the engine, the load of the engine, the intake manifold temperature of the engine, the intake air mass flow, the fuel flow into the engine, the intake manifold pressure of the engine, and exhaust gas flow out of the engine, (c) directing a first quantity of a reluctant into the exhaust line upstream of the NOx adsorber at the regeneration cycle, and (d) oxidizing the first; quantity of the reluctant within the exhaust gas and upstream of the NOx adsorber to maintain a lambda of the regeneration flow of less than one across the NOx adsorber.
A further aspect of this method comprises introducing hydrogen into the regeneration flow by reforming a second quantity of the hydrocarbon within the exhaust gas upstream of the NOx adsorber.
With regard to the introduction of a hydrocarbon comprising methane into the aftertreatment system, in one embodiment of the method, the hydrocarbon can be oxidized within the exhaust gas prior to directing the bypass flow around the NOx adsorber. However; in a preferred embodiment the hydrocarbonis oxidized within the regeneration flow. In these embodiments, the first quantity of the hydrocarbon can be directed into the exhaust gas by at least one of a valve or an injector.
In another embodiment of the method of operating an internal combustion engine equipped with an aftertreatment system, the regeneration cycle end time is based on the lambda of the regeneration flow downstream of the NOx adsorber being representative of an oxygen potential below a pre-determined threshold concentration. In a further embodiment, the regeneration cycle is based on a concentration of the reductant downstream of the NOx adsorber being above a pre-determined threshold concentration.
In another embodiment of the introduction hydrogen into the regeneration flow by reforming a second quantity of the hydrocarbon within the exhaust gas upstream of the NOx adsorber, the regeneration cycle end time is based on a concentration of at least one of CO or H2 downstream of the NOx aelsorber being above a pre-determined threshold concentration.
In another embodiment of the method of operating an internal combustion engine equipped with an aftertxeatment system, the regeneration flow is controlled by at least one valve. In a particular embodiment, the regeneration flow is controlled by a,bypass valve in a bypass line and an exhaust valve in an exhaust line. For greater control over the regeneration and bypass flows, each one or both of the bypass valve and the exhaust valve can be a variable control valve.
In another embodiment of the method of operating an internal combustion engine equipped with an aftertreatment system, the regeneration cycle start time is determined based on the measurement of a NOx concentration within the exhaust, gas downstream of the NOx adsorber, with the start time occurring when the measured NOx g -concentration is higher than a threshold concentration, which is determined by reference to a NOx concentration of the exhaust gas exiting from the engine.
In embodiments of the method that employ methane as the hydrocarbon, the method may further comprise reducing and oxidizing the exhaust gas in the combustion chamber, when operating in a predefined low load, low speed mode.
An aftertreatment system is provided for treating NOx found in exhaust gas produced during combustion of a fuel within a combustion chamber of an operating internal combustion engine. This system comprises:
(a) an exhaust line for directing the exhaust gas from the engine, (b) a NOx adsorber disposed in the exhaust line;
(c) a regeneration catalyst disposed in the exhaust line upstream of the NOx adsorber, with such regeneration catalyst capable of oxidizing a reductant;
(d) a reductant line for delivering the reductant to the exhaust line upstream of the regeneration catalyst;
(e) a bypass line for directing the exhaust gas around the NOx adsorber, (f) at least one valve capable of controlling flow of the exhaust gas' through the bypass line, (g) a controller, and (h) at least one sensor providing control information to the controller, the controller capable of adjusting the at least one valve in response to the control information.
With this aftertreatment system, the reluctant can be hydrogen. This aftertreatment system can also use a reluctant that is a gaseous hydrocarbon, with the regeneration catalyst in this embodiment being capable of reducing the gaseous hydrocarbon to provide hydrogen with the exhaust gas.
In a preferred embodiment of the aftertreatment'system, the regeneration catalyst comprises a reformer in evies with an oxidation catalyst. The regeneration catalyst can also be a POX. In another embodiment, the regeneration catalyst comprises an oxidation catalyst combined with a reformer.
The aftertr~atment system can further comprise a second close=coupled catalyst proximate to the engine for oxidizing the reluctant when the exhaust gas proximate to the regeneration catalyst is at a temperature below a predetermined threshold temperature. The predetermined threshold temperature is determined as the temperature below which the reduction catalyst is unable to efficiently oxidize the reluctant.
The aftertreatme~t system can further comprise an injector for, injecting the reluctant into the exhaust line.
The bypass valve can be a variable control valve for improved modulation of flow through the by-pass.line.
A further embodiment introduces a second quantity of the reluctant such as hydrogen or a hydrocarbon through a second gas line to deliver it to the oxida ion catalyst.
Further aspect of the invention and features of specific embodiments o~ the invention are described below.

Brief Description of the Drawings In drawings which illustrate non-limiting embodiments of the invention:
Figure 1 shows a schematic of a NOx management system according to one embodiment of the invention.
Figure 2 shows a graphical representation of properties of the exhaust gas plotted against time. Included are some system properties over a regeneration cycle.
Figure 3 shows an engine operating map of torque against speed with flow gradients over a regeneration cycle provided for use in a closed-loop control strategy:
Figure 4 show a graph of flow versus temperature of the exhaust gas out of the engine and through the NOx catalyst during regeneration.

Detailed Description A method of regenerating a NOx adsorber is disclosed for a NOx adsorber that is used to treat exhaust gases created during combustion in the combustion chamber. A hydrocarbon, preferably methane, is introduced into the exhaust line wherein the hydrocarbon is oxidized and reformed within the exhaust line to generate hydrogen which is used to regenerate the NOx absorber. C0, as well as hydrogen, is generated during reformation of methane resulting in a regeneration mixture that includes both hydrogen and CO. The aftertreatment system is capable of directing an amount of exhaust gas to by-pass the NOx adsorber during regeneration for the purposes of reducing regeneration flow, hydrocarbon consumption, emissions, and regeneration time. Specific markers, indicative of the properties of the exhaust gas, can be used to identify completion of regeneration.
Figure 1 is a schematic showing a preferred embodiment of the subject aftertreatment system.
An exhaust line 22 carries exhaust gases flowing in the direction of arrow 20 from an engine block 11 to an outlet in the direction of arrow 31.
Components of a NOx aftertreatment system can be disposed in exhaust line 22 such that exhaust gases are carried to NOx adsorber 46 a.s indicated by arrow 56. Regeneration catalyst 42 is disposed in exhaust line 22 upstream of NOx adsorber 46.
By-pass line 12 is capable of carrying a portion of the exhaust gases around adsorber 46 as may be desirable while absorber 46 is being regenerated. The exhaust gases can be directed through by-pass line 12 as indicated by arrow 18 by opening by-pass valve 14. By-pass valve 14 can be disposed anywhere along by-pass, line 12. Tn the embodiment shown, by-pass line 12 branches off from exhaust line 22 at a junction 16 and rejoins exhaust line 22 at a junction 48 downstream from NOx adsorber 46.
Valves 13 and 14 are provided to help control the flow of exhaust gases through line 22 and by-pass line 12 during regeneration.
Close coupled catalyst 74 is provided in line 22 physically proximate to engine block 11. A
hydrocarbon, preferably methane gas, can be introduced just prior to catalyst 42 and / or catalyst 74. Hydrocarbon valves 28 and 29 are disposed in respective main line 26 and close couple line 27, each of which branches off of store line 34. Store line 34 is connected to store 36 from which methane is allowed to flow as indicated by arrow 50. Flow direction 51 and 52 along lines 26 and 27 are also provided.
Lambda sensor 71 is used to measure lambda.
Lambda, is defined herein as a measure of the oxygen potential of the exhaust gas. A lambda sensor measures this potential. Generally, a lambda value above 1 denotes a high oxygen potential and a lambda value below 1 denotes a low oxygen potential. A rich exhaust gas environment is an environment with a lambda value below 1 while a lean exhaust gas environment is an environment with a lambda value above 1. Lambda sensor 71 measures lambda in the exhaust gas after adsorber 46 and also near engine block 11 as shown by the intersection point of feed lines 61 and 63 with exhaust line 22. NOx sensor 72 is used to measure NOx levels after adsorber 46 and near engine block 11 as shown by the intersection point of feed lines 62 and 64 with exhaust line 22.
Temperature sensor 73 is also used to measure temperatures before and after catalyst 42 as show by the intersection point of feed lines 65 and 66 with exhaust line 22. Finally, each of sensors 71, 72 and 73 feed information to controller 70 through respective feed lines 67, 68 and 69. Line 60 provides engine data to controller 70.
Controller 70 drives valves 13 and 14, through feed lines 75 and 76, and valves 28 and 29, through feed lines 77 and 78.
Figure 2 provides a graph demonstrating a sample set of conditions within the exhaust gas at a typical mid-range engine speed and load plotted against time. Line 500 is lambda of the exhaust gas measured at point C. Line 502 is the temperature of the exhaust gas measured in degrees Celsius at point A. Line 504 is the flow of the exhaust gas at point B measured in kg/hr. Line 506 is the NOx concentration of the exhaust gas measured downstream of adsorber 46 at point D, in ppm. Line 508 is lambda of the exhaust gas at point B and line 508 overlaps line 500 except for the dashed line indicated by reference number 508 between the start and end of the regeneration cycle. Line 510 represents a lambda value of l, above which the exhaust gas has high oxygen potential and below which the exhaust gas has a low oxygen potential. Line S provides the approximate start time of a regeneration cycle.
Line O provides the earliest end to a regeneration cycle. Line F provides the end of the regeneration cycle in the example shown.
Figure 3 provides an engine map of torque versus speed. Lines 900 through 906 provide gradient lines that demonstrate the boundaries at which 100x, 500, 35o and 200 of the total exhaust gas flow is directed through the NOx adsorber during regeneration. Line 908 deffines the boundary of the engine operating map.
Figure 4 provides a graph of flow or space velocity of the exhaust gas plotted against temperature. Line 800 provides an example of exhaust gas properties out of engine block 11 over all operating conditions of the e:~gine. Line 802 provides target properties of the exhaust gas through NOx adsorber 46 during regeneration.
In the NOx aftertreatment systems of Figure 1, exhaust gas is generated by combustion events within one or more combustion chambers disposed upstream of engine exhaust line 10 in engine block 11. Exhaust gas results from the combustion of fuel such as natural gas or a mixed fuel that includes natural gas or methane. The fuel is, in general, either directly injected. into the combustion chamber or pre-mixed with a quantity of air to create a fumigated charge. In each case, spark ignition, hot surface ignition or compression ignition are utilized to initiate the combustion process within the combustion chamber.

During normal operation of the engine valve 14 is closed and exhaust gas flows along exhaust line 22. The exhaust gas also passes through NOx adsorber 46 which removes NOx. By way of example, during normal operation, NOx adsorber is under lean operating conditions, that is, with an excess of oxygen available in the exhaust gas, NOx is driven to (N03) 2 by way of the following reactions:
N0 + '~ 02 ( Pt ) -~ N02 ( 1 X0 + 2 N02 + '~ 02 ~ X ( N03 ) 2 ( 2 where X is a washcoat, as is well known to those skilled in this technology. Eventually NOx adsorber 46 will become less effective at removing NOx as X(N03)2 uses up adsorbing sites in adsorber 46. NOx slip is used to express a percentage increase in NOx emissions above a baseline concentration. NOx slip can be used to determine when an unacceptable level of NOx is being expelled. When this unacceptable level is reached, adsorber 46 can be regenerated in order to ensure continued removal of NOx from the exhaust gas. Controller 70 determines when NOx adsorber 46 needs regenerating. This can be done through an open loop control, based on selected parameters from the engine map, or closed loop control, based, in part, on directs readings of the NOx concentration within the treated exhaust gas.
By way of example, one such open loop control would use a calibration of the treatment system over a range of engine operating conditions to estimate the time at which adsorber 45 needs regeneration. What is, the controller would monitor such variables as the engine load and speed, determining from a look-up table, the time for regeneration. With this method, the system is calibrated such that the engine operating conditions, which are indicative c>f NOx production, are used to estimate when :regeneration for the NOx adsorber is desirable. Conditions such as torque, speed, intake air mass flow, the fuel flow into the engine, intake manifold temperature, intake manifold pressure, as well as others, can be used for open loop control.
A closed loop control for determining the commencement of a regeneration cycle could also be used. By way of example, one such control would monitor NOx levels within exhaust line 22 downstream of adsorber 46 with sensor 72 through line 64 and near the engine through line 62. Once the controller detects relative increases in the ratio of NOx at point C to NOx out of block 11, controller 70 can commence regeneration once a predetermined threshold NOx slip is exceeded for a given set of engine operating conditions.
During the regeneration cycle, controller 70 needs to provide HZ and/or CO to NOx adsarber 46 and do so in a rich exhaust gas environment (oxygen depleted environment). 'fhe controller can control exhaust gas flow and the introduction of methane to provide a regeneration strategy that will help to limit the use of hydrocarbons, such as methane, while reducing regeneration time.

- ~.9 -During regeneration, the following provides a preferred set of reaction =conditions across catalyst 42:
CH4 + 202 ~ C02 + 2H20 ( 3 ) CHa_ + ~z02 ~ CO + 2H2 ( 4 ) CH4 + H20 -~ CO + 3H2 ( 5 ) CO + H20 H C02 + H2 ( 6 ) where reaction 6 can be held in equilibrium depending on exhaust gas temperature. The CO and H2 generated according to equations 4 through 6 are then used for regeneration as follows:
X(N03)2 ~ XO 2N0 + 3/2 02 (7) +

X ( N03 ) 2 ~ XO 2N02 + '-X02 ( 8 +

NO + HZ -~ H20 '-~N2 ( 9 + ) N02 + 2H2 -~ + 2H20 ( 10 '-~N2 ) NO + CO ( Rh ) ~ '~N2 + C02 ( 11 ) N02 + 2C0 ~ + 2C02 ( 12 '-zN2 ) where X is provided in a washcoat. A lambda less than 1, which denotes a law oxygen potential in the exhaust gas, favors reactions 7 through 12;
this is not the case when lambda is above 1.
Controller 70 determines a regeneration strategy based, generally, on the exhaust gas flow, the exhaust gas temperature, a desired exhaust gas flow chosen considering the reactive capacity of catalyst 42 at a given exhaust gas temperature, and lambda of the e~;haust gas from the engine, adsorber 46 and/or catalyst 42 throughout a regeneration cycle. The catalyst 42 is chosen to suit the engine used and the operating conditions contemplated for the engine.
The regeneration strategy for a given regeneration cycle can be done by an open loop or closed loop strategy. The regeneration strategy can control the quantity and rate of introducing the methane into the aftertreatment system from store 36 and the quantity of by-pass flow by controlling valves 13 and 14. The goal during regeneration is to efficiently provide an exhaust gas environment wherein lambda is below one, thereby promoting reactions 7 through 12. This is realized when reductants are provided to the NOx adsorber that remove oxygen relea:~ed according to the reactions above. However, oxidation through the NOx adsorber with other reduct:ants such as methane or other hydrocarbons can also provide-the necessary rich exhaust gas environment.
In an open loop strategy. the controller is preferably calibrated to direct flow of exhaust gas through the adsorber and methane into the exhaust gas based on the engine speed and load just prior to and during regeneration. Engine intake manifold temperature, intake air mass flow, the fuel flow into the engine or intake manifold pressure can also be used as indicators for controlling regeneration. A constant regeneration cycle time can also be used in certain static operating conditions when load and speed remain relatively constant over extended periods of time.
Such an open loop strategy employs an engine calibration that considers one or more engine operating conditions, each of which is indicative of at least ane of exhaust gas temperature, flow and lambda value. The controller is calibrated to direct a desired flow of exhaust gas through the NOx adsorber based on the characteristics of catalyst 42 and adsorber 46. For the purposes of this application, the flow through the NOx adsorber during regeneration will :be referred to as the regeneration flow. A look-up table is used to determine whether the exhaust gas flow exceeds the desire regeneration flow and, if so, directs excess exhaust gas around adsorber 46 via by-pass line 12. This is referred to as the by-pass flow if exhaust gas is by-passed during regeneration.
The desired by--pass flow is achieved by adjusting valves 13 and 14 to match the target regeneration flow though adsorber 46. ~2eferring to the engine map of fig. 3, the percentage flow of exhaust gas through NOx adsorber 4~ is provided based on the torque and speed of the engine and this percentage is reduced as speed and torque increases, as is seen in contour lines 900 through 906. Operating conditions falling above or to the right of line 900 show a reduction in the proportion of the total exhaust gas that flows through adsorber 46.
Below and to the left of line 900, controller 70 does not open valve 14 allowing all exhaust gas to flow through adsorber 46.
The look-up table for this open loop control also provides a target methane concentration upstream of catalyst 42. The engine operating conditions provide information about th.e exhaust gas temperature and lambda of the exhaust gas from block 11. The temperature of the exhaust gas determines the amount of methane required in order to meet the target temperature range for the exhaust gas during regeneration. 'This target temperature range should be held below a temperature that might damage the catalyst and above a temperature suitable for efficient reformation of methane and regeneration of NOx adsorber 46. Moreover, the lambda of the exhaust gas, estimated from the engine operating conditions, determines the amount of methane required to generate a sufficiently rich exhaust gas environment to support efficient regeneration.
A closed loop strategy could .also be used wherein lambda would be measured ovt of engine block 11 by sensor 71 and the temperature would be measured prior to catalyst 42 by sensor 73 through line 66 and after catalyst 42 through line 65.
The load and speed of the engine could be used by the controller to infer the exhaust gas flow based on look-up tables or a flow meter within the exhaust line could also be used for complete closed loop control. The look-up table along with sensor information are used to determine the flow of methane to be introduced into exhaust line 22 and how much flow of exhaust gas, if any, to direct through valve 14 and line l2 during regeneration. When exhaust gas flow is too high for catalyst 42 to allow complete oxidation and reformation of methane or too high to regenerate efficiently, some flow is directed into by-pass line 12 until the desired flow is met. If temperature prior to and after catalyst 42 is too high or too low, the methane quantity can be increased or reduced according to those temperature readings. For example, if the temperature fell below a predetermined temperature set during calibration and based, in part, on the catalyst chosen, methane could be reduced to ensure that the exhaust gas temperature is elevated to an acceptable level to support the reformation reaction 5 set out above. Further, if the post catalyst temperature is too high, the methane quantity can be shut-off to avoid overheating the catalyst and damaging it during regeneration. Such a strategy can employ a series of cycles whereby the methane flow through valve 28 is opened and closed a few times through one regeneration cycle to ensure that adsorber 46 is regenerated while protecting catalyst 42.
Likewise, lambda sensor 71 can allow the controller to adjust the quantity of methane introduced through valve 28 to ensure that the exhaust gas was rich enough to approach target regeneration efficiency across adsorber_ 46 according to reactions 7 through 12 set out above.
Also, a lambda sensor could be used after catalyst 42 and before adsorber 4~ rather than, or in addition to, sensor 71 provided. This would monitor the oxygen potential out of catalyst 42 to provide for efficient regeneration through adsorber 46. That is, if the flow of methane through line 26 is unknown, then the lambda sensor could be used to close loop control the flow of methane to help provide for a target lambda in the regeneration flow prior to regeneration of NOx adsorber 46.
An optional close-coupled catalyst 74 is also available to increase exhaust gas temperatures when desired. The proximity of catalyst 74 to block 11, helps ensure that exhausl= gas is never too cool to oxidize methane within the exhaust gas environment. Therefore, when the controller detects an exhaust gas temperature below a threshold amount, valve 29 will provide methane upstream of catalyst 74, heating and oxidizing the exhaust gas well upstream of adsorber 46.
Catalyst 74 can also be used to produce CO and hydrogen for use in regeneration a.s was done with catalyst 42.
As noted above, these closed loop strategies are preferred but they are not necessary. The open loop strategy discussed above utilizing a calibration of the system 'that provides a target methane injection rate and quantity over a regeneration cycle that is based on the engine operating parameters such as load and speed, could eliminate dynamic monitoring and the added complexity in hardware and software for the system. However, the trade-off is that. such a strategy is more likely to regenerate incompletely or to regenerate with a higher methane penalty.
The controller can determine completion of a regeneration cycle by reference to a closed or open loop control. In a closed loop control, the controller can use readings from lambda. sensor 71 downstream of adsorber 46 to determine when the oxygen potential within line 22 downstream of adsorber 46 is decreasing. Referring to reactions 7 through 12, once most nitrogen has been released from adsorber 4~, oxygen potential begins to decrease as oxygen is no longer being released from adsorber 46. Other sensors may be appropriate for closed loop monitoring of regeneration cycle completion, inc:Luding a CO or HZ sensor that would detect increases in CO or HZ
downstream of adsorber 46. These :increases would occur when oxygen is no longer release from the adsorber causing H2 and CO to pass through the adsorber unreacted.
An open loop control could also be used relying on the calibration of the .system wherein regeneration time is pre-determined based on engine operating conditions such as speed, load, intake air mass flow, the fuel flow into the engine, intake manifold temperature and pressure.
Referring again to fig. 3, as either or both speed and load of the engine at the commencement of and during a regeneration cycle increase, controller 70 commands valve 14 to open when load and speed fall above line 900. Valves 13 and 14 can be variable control valves providing for a wide range of operating conditions as the engine operating parameters continue to generate exhaust gas flows above a target flow through catalyst 42 or adsorber 46 determined, in part, by the properties of catalyst 42. Therefore, when controller 70 determines a desired exhaust gas flow, valves 13 and 14 can be adjusted to maintain this pre-determined flow of exhaust gas through line 22 during regeneration.
To simplify the system, an alternative to variable flow control valves used for valve 13 and 14 are 2 position valves (or for that matter other multiple position valves). Here, the controller can elect from one of 3 possible settings. Valve 13 can be fully open or partially open. Valve 14 can be closed or fully open. Therefore, controller 70 can select a positio:r~ for each valve according to the engine operating parameters in order to match exhaust flow through line 22 to a pre-determined target value. That is, at low speed and load, valve 13 is open fully and valve 24 is closed. At higher loads'and speeds, valve 13 is fully opened and valve 14 is ful=ty opened.
At still higher speeds and loads, valve 13 is partially closed and valve 14 is opened.
Other valve configuration can be used as well. More flexibility for the controller to manage flow through line 22 during regeneration helps the controller to meet a target pre-determined flow rate for each operating condition.
One trade-off is that such flexibility rnay result in a more expensive system that requires more expensive valves and more complicated software to control those valves.
As would be understood by a person skilled in the technology, valves 13 and 14 can be any flow control mechanism and need not be limited to valves.
Referring to fig. 4, flow and temperature over the range of engine operating conditions are provided. Area 800 shows typical exhaust gas flow and temperature conditions expelled from block 11.
Area 802 provides the controller a desired operating range for temperature and flow of exhaust gas through NOx a.dsorber 46 during regeneration. Therefore, when the flow out of block 11 is above area 802, flow through bypass line 12 can be used to bring the exhaust flow through adsorber 46 to within area 802 and below the upper limit flow or upper flow of the range.
Tdeally, regeneration flow is targeted to a desired flow within this range, however, depending on such things as exhaust gas flow, valve reaction times in the system, pressure and temperature changes, a different regeneration flow within the range defined by 802 is all that can be maintained. When the temperature falls below area 802 (to the left of area 802) at catalyst 42, additional heat can be generated through the operation of the engine as described below or using close coupled catalyst 74, proximate to block 11, as described above and below.
Referring to fig. 2, selected properties of the system are plotted over the course of a a partial adsorbing cycle and an entire regeneration cycle. Referring to fig. 1, lambda at points B
and C (lines 508 and 500, respect:fully), temperature and space velocity at point A (lines 502 and 504 respectfully) and NOx at point D (line 506) are all shown, plotted against time. The example provided is representative of operation of the aftertreatment system when an engine is running at a typical midrange speed and load.
Referring to line 506, NOx concentrations increase gradually until the controller is determines that the level has exceeded a pre-determined threshold - this could be done by monitoring the engine operating parameters or measuring the NOx concentration. Regeneration then commences with opening of valve 14.

Commencement of regeneration is shown at time S.
Opening valve 14 drops the space velocity or flow through line 22, line 504, at time S. Methane is also directed into line 22 causing lambda to drop to a level below 1 between catalyst 42 and adsorber 46 (line 508). Lambda following the NOx adsorber also drops after regeneration is complete, (line 500), but during :regeneration of the adsorber, it is maintained near a lambda value of 1 as the rich mixture entering the adsorber releases oxygen from the oxides of nitrogen resulting in a leaner mixture expelled from adsorber 46 than that entering adsorber 46.
Eventually, however, no further oxygen is released from adsorber 46 and lambda falls unt~_1 the lambda out of adsorber 46 is the same as lambda into adsorber 46, (line 508). Once a threshold lambda out of adsorber 46 is detected, valve 14 is closed along with valve 28. Immediately, the flow begins to rise, line 504, as all exhaust gas is again routed through exhaust line 22. Soon, lambda begins to rise resulting in a lean exhaust gas environment, lines 500 and 508.
Note, that the regeneration cycle is complete at time F in fig. 2. This is, in practice a delayed end of the regeneration cycle.
Preferably, the regeneration cycle would be completed sometime between time 0 and. time F when lambda after the NOx adsorber (line 500} drops below a pre-determined threshold amount and before it matches lambda upstream of the NOx: adsorber (line 508}.

During the regeneration cycle, the NOx levels out of line 22 increase substantially, as the engine is continuing to operate without NOx treatment of the exhaust gas routed through by-pass line 12, line 504. Once regeneration is complete, however, NOx quickly falls as all exhaust gas is routed through recently regenerated adsorber 46. Therefore, as well as a desire to reduce fuel consumption (consumption of methane), short regeneration times also limit the amount of NOx emitted during regeneration through by-pass line 12. The longer the period of time needed for regeneration, the more cumulative exhaust gas flows through by-pass line 12. The target cycle is based on generating as much reductant per unit methane injected aver the shortest time period.
This is a function of variables su~~h as the temperature of the exhaust gas, flow of exhaust gas, catalyst specifications, and .lambda of exhaust gas, since a higher lambda requires more methane to burn off the oxygen present.
Preferably, regeneration cycles should be kept to less than So of operating time of the engine.
Also, as noted above, a greater flow of exhaust gas routed through by-pass line 12, results in higher NOx emissions since by-pass line 12 does not generally include a separate NOx adsorber. In an alternate embodiment of the aftertreatment system, a second NOx adsorber and catalyst could be disposed in the by-pass line to treat NOx through that line during regeneration.
Eventually, this NOx adsorber, as well, would need to be regenerated. In this two-bed aftertreatment system, line 22 could be treated as the by-pass line during regeneration when the methane store feeds methane to line 12 for the purposes of regeneration.
An alternative method of operating the aftertreatment system that can help to reduce regeneration time employs an additional exhaust line that routes exhaust gas around catalyst 42 and through adsorber 46 during regular operation.
A valve disposed in this additional exhaust line could be used such that valve 13, closed during regular operation, would be opened just prior to commencement of regeneration, while maintaining the catalyst bypass open. This would allow a flow of exhaust gas through line 22, lighting off catalyst 42 and warming the line prior to a regeneration cycle. When a valve used to bypass catalyst 42 is closed at the beginning of a regeneration cycle, there is less time needed to heat line 22 and less time before regeneration can commence. Alternatively, in such an embodiment with an additional exhaust line around catalyst 42, the flow rate within reformer line 22 can be set to ensure a certain amount of exhaust gas is always flowing through line 22 eliminating the need for valve I3 by employing a valve to regulate flow through catalyst 42 by controlling flow through the additional exhaust line.
Catalyst 42 is generically describe as a bed that promotes reactions 3 through 5 to provide a desired exhaust gas with elevated concentrations of H2 and/or CO and minimal amounts of oxygen. To varying extents, reactions 3 through 6, a combination of exothermic and endothermic reactions, drive the process acro~~s this catalyst.
This catalyst can be a reformer that oxidizes methane and promotes reaction 5 to provide H2 and C0. It can also be a partial oxidation catalyst, that partially oxidizes methane and re:Eorms methane to provide H2 and CO, see .reaction 4.
Catalyst 42 can also be a back-to-back oxidation catalyst and reformer sharing a common boundary surface. This catalyst would first oxidize methane until little oxygen remains within the exhaust gas and then, use excess methane to generate HZ and CO within the reformer. These two catalysts, the oxidation catalyst and reformer, ~5 can also be disposed in line 22 in series and need not share a common boundary surface. Also, a combination reformer and oxidation catalyst could be used that integrates the reformer and oxidation catalyst together in a mixed catalyst. Each option has balancing cost and efficiency considerations that weigh in any decision. as to which catalyst to use depending on the aftertreatment system sought.
As noted briefly above, referring again to fig. l, an additional catalyst, close coupled catalyst 74, is shown positioned near engine block 11. Some systems need such a catalyst disposed close to the engine to ensure that the exhaust gas is hot enough to support oxidation of methane.
That is, there are some aftertreatment system designs that would benefit from employing a close coupled catalyst near the engine block so that the exhaust gas temperature under low load and / or speed or idle conditions can be prevented from falling below a threshold limit at. which stable oxidation of methane in catalyst ~E2 would be compromised. Therefore, under such conditions, there are advantages in having close coupled catalyst 74 near engine block 11 with line 27 feeding methane upstream of such catalyst. This catalyst would then either oxidize the methane provided from store 36 to heat the exhaust gas to a temperature suitable to allow catalyst 42 to light off satisfactorily. Alternatively, catalyst 74 can provide the rich exhaust gas environment along with H2 and CO needed to regenerate adsorber 46. It would be desirable here, however, to operate this way only wherx valve 1.4 is closed in order to prevent CO and HZ from escaping through the by-pass line, since this would be inefficient.
An additional method of operating the regeneration cycle under low load conditions is to burn a fuel rich combustible mixture, preferably comprising methane, in the combustion chamber within engine block 11. Z'his will. generate an excess of CO and some HZ while creating a rich exhaust gas environment. With this method, no methane needs to be provided to catalyst 42 when the necessary reductants are present within a rich exhaust gas environment. Preferably, such a strategy would be limited to light. load and low speed conditions or idle conditior.~s when full flow through adsorber 46 is desirable.
As noted above, the regeneration cycle is dependant on the exhaust gas temperature. It is important that the exhaust gas introduced into catalyst 42 have a temperature above a minimum temperature to ensure that the cat:alyst is "lit-off" initially. An additional way of controlling the regeneration process from the combustion chamber is to choose a combustion strategy or combustion timing that ensures either :relatively late heat release, as might be the case with spark ignited engines, or a delayed or second direct injection of fuel into the combust:ion chamber late in the power stroke when regeneration :is required.
This can also reduce NOx levels with associated benefits during regeneration as a quantity of exhaust gas can be directed through the by-pass line without NOx treatment. A reduced IVOx level has benefits here. Other strategiE:s are well known to persons skilled in the art.
As natural gas is, overwhelmingly,, methane with a few additional heavier hydx°ocarbons, CZ and C3 hydrocarbons in general, the methane store 36 can be the fuel storage tanks if t:he engine is fueled by natural gas. That is, methane store 36 can be a natural gas source such as the engine fuel tanks.
Also, valves 28 and 2.9 can be injectors that would directly inject methane into exhaust line 22. An injector as the reluctant flow control would provide greater control over the timing and quantity of methane and, therefore, greater control over the regeneration cycle.
A metal substrate for carrying the catalyst is generally preferred, rather than, for example, a ceramic substrate, if tree metal substrate improves thermal response to catalyst 42. As noted above, the quicker the thermal response the quicker the regeneration process can be completed, thereby reducing the amount of untreated exhaust gas allowed to flow through by-pass line 12.
An additional embodiment of the aftertreatment system can include a valve for introducing methane downstream from an oxidation catalyst and upstream of a reformer with catalyst 42 comprising an oxidation catalyst and reformer in series but not sharing a common interface.
Flow of methane through such a downstream valve can be controlled in response to the quantity of methane needed within the exhaust gas entering a reformer. After the exhaust gas has passed through an oxidation catalyst its properties are changed.
There will be less oxygen within the gas and less methane. This is because oxidation of methane occurs within catalyst. This consumes oxygen. As methane serves to provide the source for H2 and CO, which are preferred components in the regeneration process (see reactions 4 and 5 above , the quantity of methane needed within the reformer is determined by the amount present within the exhaust stream upstream of the reformer. The amount of methane preferred is determined by that present in the gases which are exiting the oxidation catalyst and the HZ and CO
concentrations preferred in light of this initial quantity of methane present, which is the methane not oxidized within oxidation catalyst.
Once forced through the oxidation catalyst, the exhaust gas, supplemented with methane via a downstream valve, is forced through the reformer.
The reformer utilizes the high temperature of exhaust gas heated in the oxidation catalyst and the combustion chamber to drive reformation of methane withir: the reformer in lire 22 to provide HZ and CO downstream from catalyst 42. This stream is directed into NOx adsorber 46 when HZ and CO
regenerate NOx adsorber 4E.
An oxidation catalyst can be a component of catalyst 42, and can be any oxidization catalyst suitable for oxidizing the exhaust gas to reduce the oxygen content. By way of example, a suitable oxidation catalyst can promote the: following reactions:
CxHy + ( x+y/ 4 ) 02 ( Pt ) °~ xCO~> + y,~ 2 H20 CxHy + (x+y/4) OZ (Pd) ~ xC02 + y/2 Hz0 1.5 CxHy + (x/2 ) OZ ( Pd) -~ xC0 + y/2 HZ
CO + '~ O2 -~ COZ
By way of example only, for the operating conditions known for this application, a suitable washcoat formulation comprises A1203. Other suitable washcoat formulations may also be used, as would be understood by a person skilled in the art.
A reformer can be a component: of catalyst 42, and reformers suitable for this application are well known. The reformer is preferably suitable to convert methane with water to CO a:nd H2. By way of example, the reformer can be a precious metal-based catalyst with washcoat materials including A1203 .
NOx adsorber 46 typically adsorbs and stores of NOx in the catalyst washcoat while operating under lean conditions and N02 can :be released and reduced to NZ under rich operating conditions when a regeneration mixture, that includes hydrogen and rich exhaust gas, is passed through the adsorber.
As noted above, the following shows typical operation of the NOx adsorber undo r lean conditions:
NO + '-z Oz ( Pt ) -~ NO2 XO + 2 N02 + %~ 02 -°l X (N03) 2 and under rich conditions:
X (N03) 2 ~ XO + 2N0 + 3/2 OZ
X ( N03 ) 2 -~ XO + 2N02 + '~ OZ
NO + CO ( Rh ) ~ '-~ N2 + C02 2N02 + 4H2 -~ NZ + 4H20 where X is provided in the washcoat and is typically an alkali (eg., K, Na, Li, Ce), an alkaline earth (eg., Ba, Ca, Sr, Mg) or a rare earth (eg., La, Yt).
An inline external heater can be used to help light off catalyst 42 and promote reformation and oxidation of exhaust gas during regeneration.
While, it is preferable that the majority of heat is provided by the exhaust gas, things such as, by way of example and not limited to:
transient response, efficiency considerations, combustion strategies that utilize a quick heat release, valve timing or cylinder design that takes advantage of a large expansion ratio can release exhaust gas that could benefit from such a heater in order to initiate oxidation prior to or during regeneration.
A heat exchanger could direct a quantity of heat from the outlet of catalyst 42 or heat from gases unused after regeneration out of adsorber 46 back through to a point along line 22 upstream of catalyst 42. This could be used to help reduce the load on such heater after it init=sally lights the catalyst off.
Note that for reforming, as rioted above, steam is required in order to generate HZ and CO
for regeneration. This need tends to be met as exhaust gas has sufficient quantities of water.
However, if water levels are low, a partial oxidation catalyst (POX) catalyst can be employed to reform the gas without the need for supplemental water: see reaction 4. Other reformers could be used as understood by a person skilled in the art.
Steam is made more available by oxidizing methane as compared to other hydrocarbons. This is an additional advantage in light of the above.
A further advantage can be realized if a fuel is used that combines methane and hydrogen as two major components. By way of example, natural gas with 10 to 50o hydrogen might be appropriate as an engine fuel and appropriate for rE:generation. Such a fuel could then be util~_zed in t;he embodiments discussed wherein the hydrogen introduced with the fuel prior to the oxidation catalyst could help to light off those catalysts and help to provide an exhaust gas environment with a lambda less than 1.
Further, by providing a quantity of hydrogen into the exhaust stream, the burden on catalyst 42 is reduced. Less reforming is required for regeneration due to the presence of hydrogen in the injected fuel.

- 3~i -The method taught above for bypassing exhaust gas can also be used if hydrogen is injected into the exhaust gas. Here, the regeneration strategy is driven by a target regeneration flow through the NOx adsorber that would efficiently regenerate while limiting the associated fuel penalty and release of untreated NOx and NOx slip during regeneration. This is that much more beneficial if the engine is fueled by hydrogen, with the fuel providing a ready source of reduct;ant, but this method would be useful, as well, if an external reformer can be used. Further, use of a two-bed aftertreatment system, as discussed above, would be useful if hydrogen can be direcaly injected into the exhaust gas upstream of a NOx adsorber during a regeneration cycle after determining a target regeneration flow.
Whenever flow is referred to in t:~is disclosure, it is the mass or molar flow rate of the gas in question.
Exhaust gas recirculation (ECJR) can also be utilized to help reduce NOx emissions during regeneration when a by-pass line i_s opened.
Increased EGR rates during regeneration can reduce NOx generated in the combustion chamber resulting in less NOx flowing through by-patss line 12 and into the atmosphere. Furtraer, increases in EGR can also be used to reduce the concentration in oxygen in the exhaust gas during regeneration, reducing, in turn the burden on the oxidation catalyst to reduce oxygen during a regeneration cycle as well as reduce the amount of methane needed to burn off oxygen.

While methane is the preferred source for hydrogen, as would be understood by a person skilled in the art, other lighter hydrocarbons, generally, gaseous hydrocarbons, could be used including but not limited to other gaseous hydrocarbons such as ethane, propane and butane.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be ur.~derstood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the scope of the present disclosure, particularly i.n light of the foregoing teachings.

Claims

That is claimed is:

1. A method of regenerating a NOx adsorber, said 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:

determining a target regeneration flow of said exhaust gas through said NOx adsorber, directing a regeneration flow of said exhaust gas through said NOx adsorber, said regeneration flow established by one of:

bypassing a bypass flow of said exhaust gas around said NOx adsorber when said target regeneration flow is less than the flow of said exhaust gas 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 NOx adsorber when said target regeneration flow is greater than the flow of said exhaust gas from said engine, said flow of said exhaust gas from said engine and said bypass flow determined by reference to at least one of:

the speed of said engine, the load of said engine, the intake manifold temperature of said engine, the intake air mass flow, the fuel flow into said engine, the intake manifold pressure of said engine, and exhaust gas flow out of said engine, directing a first quantity of a reluctant into said exhaust line upstream of said NOx adsorber, oxidizing, within said exhaust gas and upstream of said NOx adsorber, said first quantity of said reluctant to maintain a lambda of said regeneration flow of less than one across said NOx adsorber.

2. The method of claim 2 wherein said reluctant is hydrogen.

3. The method of claim 2 wherein said reluctant is a hydrocarbon.

4. The method of claim 3 wherein said hydrocarbon comprises methane.

5. The method of claim 4 further comprising introducing hydrogen into said regeneration flow by reforming a second quantity of said hydrocarbon within said exhaust gas upstream of said NOx adsorber.

6. The method of claim 1 wherein said fuel is the same as said reluctant.

7. 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 NOx adsorber, b. directing a regeneration flow of said exhaust gas through said NOx adsorber, said regeneration flow established by one of:

bypassing a bypass flow of said exhaust gas around said NOx adsorber when said target regeneration flow is less than the flow of said exhaust gas 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 NOx adsorber when said target regeneration flow is greater than the flow of said exhaust gas from said engine, said flow of said exhaust gas from said engine and said bypass flow determined by reference to at least one of:

the speed of said engine, the load of said engine, the intake manifold temperature of said engine, the intake air mass flow, the fuel flow into said engine, the intake manifold pressure of said engine, and exhaust gas flow out of said engine, c. directing a first quantity of a reductant into said exhaust line upstream of said NOx adsorber, d. oxidizing, within said exhaust gas and upstream of said NOx adsorber, said first quantity of said reductant to maintain a lambda of said regeneration flow of less than one across said NOx adsorber.

8. The method of claim 7 wherein said reductant is hydrogen.

9. The method of claim 7 wherein said reductant is a hydrocarbon.

10. The method of claim 9 wherein said hydrocarbon comprises methane.

11. The method of claim 10 further comprising introducing hydrogen into said regeneration flow by reforming a second quantity of said hydrocarbon within said exhaust gas upstream of said NOx adsorber.

12. The method of claim 7 wherein said fuel is the same as said reductant.

13. The method of claim 10 wherein oxidizing of said hydrocarbon occurs within said exhaust gas prior to directing said bypass flow around said NOx adsorber.

14. The method of claim 10 wherein oxidizing of said hydrocarbon occurs within said regeneration flow.

15. The method of claim 10 wherein said first quantity of said hydrocarbon is directed into said exhaust gas by at least one of a valve or an injector.

16. The method of claim 7 wherein said regeneration cycle end time is based on said lambda of said regeneration flow downstream of said NOx adsorber below a pre-determined threshold concentration.

17. The method of claim 7 wherein said regeneration cycle end time is based on a concentration of said reductant downstream of said NOx adsorber above a pre-determined threshold concentration.

18. The method of claim 11 wherein said regeneration cycle end time is based on a concentration of at least one of CO or H2 downstream of said NOx adsorber above a pre-determined threshold concentration.

19. The method of claim 7 wherein said regeneration flow is controlled by at least one valve.

20. The method of claim 7 wherein said regeneration flow is controlled by a bypass valve in a bypass line and an exhaust valve in an exhaust line.

21. The method of claim 20 wherein said bypass valve is a variable control valve.

22. The method of claim 20 wherein said exhaust valve is a variable control value.

23. The method of claim 7 wherein said regeneration cycle start time is based on a NOx concentration within said exhaust gas downstream of said NOx adsorber in excess of a threshold concentration, as compared to a NOx concentration out of said engine.

24. The method of claim 10 further comprising, when operating in a predefined low load, low speed mode, reducing and oxidizing said exhaust gas in said combustion chamber.

25. An aftertreatment system for treating NOx found in 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 NOx adsorber disposed in said exhaust line, c. a regeneration catalyst disposed in said exhaust line upstream of said NOx adsorber, said catalyst capable of oxidizing a reluctant, d. a reluctant line for delivering said reluctant from a reluctant store to said exhaust line upstream of said catalyst, e. a reluctant flow control disposed in said reluctant line for controlling flow of said reluctant into said exhaust line, f. a bypass line for directing said exhaust gas around said NOx adsorber, g, at least one bypass flow control capable of controlling flow of said exhaust gas through said bypass line, h. a controller, i. 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.

26. The aftertreatment system of claim 26 wherein said reluctant is hydrogen.

27. The aftertreatment system of claim 26 wherein said reductant is a gaseous hydrocarbon, said catalyst capable of reducing said gaseous hydrocarbon to provide hydrogen with said exhaust gas.

28. The aftertreatment system of claim 26 wherein said catalyst is a reformer in series with an oxidation catalyst.

29. The aftertreatment system of claim 26 wherein said catalyst is a POX.

30. The aftertreatment system of claim 26 wherein said catalyst comprises an oxidation catalyst combined with a reformer.

31. The aftertreatment system of claim 26 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 determined as temperature below which said catalyst is unable to efficiently oxidize said reluctant.

32. The aftertreatment system of claim 26 further comprising an injector for injecting said reluctant into said exhaust line.

33. The aftertreatment system of claim 26 wherein said by-pass flow control is a valve.

34. The aftertreatment system of claim 26 wherein said reductant store is a fuel system of said engine.