Method and apparatus for desulfurizing a NOx trap

Abstract

An emission abatement system comprises a plurality of NOX traps positioned in a parallel flow arrangement, a desulfurization agent supplier for supplying a desulfurization agent, a valve arrangement for directing flow of the desulfurization agent and internal combustion engine exhaust gas between the NOX traps, and a controller. The controller is used to control operation of the desulfurization agent supplier and the valve arrangement to desulfurize the NOX traps. An associated method is disclosed.

Description

CROSS-REFERENCE

This application claims priority as a continuation-in-part to U.S. patent application Ser. No. 10/245,884 which was filed on Sep. 18, 2002 and is hereby incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to NO_X traps.

BACKGROUND OF THE DISCLOSURE

A NO_X trap is used to remove NO_X from a stream of exhaust gas discharged, for example, from an internal combustion engine. It does so by trapping NO_X present in the exhaust gas under lean conditions and reducing the NO_X to nitrogen under rich conditions. Sulfur substances (e.g., SO_X, sulfides, elemental sulfur, and the like) present in the exhaust gas may also become trapped by the NO_X trap. Such trapping of sulfur substances by the NO_X trap may degrade the NO_X trap's ability to remove NO_X unless the sulfur substances are removed from the NO_X trap.

SUMMARY OF THE DISCLOSURE

According to a first aspect of the present disclosure, there is provided an emission abatement system having a fuel reformer under the control of a reformer controller. The fuel reformer produces a reformate gas comprising hydrogen and carbon monoxide. The reformate gas is advanced into the NO_X trap to react the hydrogen and carbon monoxide with SO_X trapped on the NO_X trap to remove SO_X from the NO_X trap (i.e., to desulfate the NO_X trap). An associated method of desulfating a NO_X trap is disclosed.

According to a second aspect of the present disclosure, there is provided an emission abatement system having a plurality of NO_X traps positioned in a parallel flow arrangement, a desulfurization agent supplier for supplying a desulfurization agent, a valve arrangement for directing flow of the desulfurization agent and internal combustion engine exhaust gas between the NO_X traps, and a controller. The controller is used to control operation of the desulfurization agent supplier and the valve arrangement to desulfurize the NO_X traps (i.e., to remove sulfur substances such as SO_X, sulfides, and elemental sulfur from the NO_X traps). An associated method of desulfurizing parallel NO_X traps is disclosed.

The above and other features of the present disclosure will become apparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an emissions abatement system including, a fuel reformer, a NO_X trap, a passageway to conduct a reformate gas produced by the fuel reformer to the NO_X trap, and wherein the fuel reformer is under the control of a reformer controller and an engine of the power system is under the control of an engine control unit which is discrete from the reformer controller;

FIG. 2 is a simplified block diagram similar to FIG. 1 except that the reformer controller is integrated into the engine control unit;

FIG. 3 is a flowchart of a control routine for desulfating the NO_X trap of FIGS. 1 and 2 after regenerating the NO_X trap (to remove NO_X trapped therein) a predetermined number of times;

FIG. 4 is a flowchart of another control routine for desulfating the NO_X trap of FIGS. 1 and 2 after a predetermined amount of time has passed since previously desulfating the NO_X trap;

FIG. 5 is a flowchart of yet another control routine for desulfating the NO_X trap of FIGS. 1 and 2 after the accumulation of SO_X within the NO_X trap has reached a predetermined amount;

FIG. 6 is a simplified block diagram of another emission abatement system comprising a plurality of NO_X traps that are desulfurized from time to time by use of a valve arrangement and a desulfurization agent supplier under the control of a controller;

FIG. 7 is a simplified block diagram of an implementation of the emission abatement system of FIG. 6; and

FIG. 8 is a flowchart of a control routine for desulfurizing the NO_X traps of FIGS. 6 and 7.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims.

Referring now to FIG. 1, there is shown an emissions abatement system 10 including a fuel reformer 12, a NO_X trap 14, and an internal combustion engine 16. System 10 is provided to desulfate NO_X trap 14 (e.g., remove or purge SO_X trapped or absorbed therein). System 10 may also regenerate NO_X trap 14 to remove NO_X trapped therein as well. Engine 16 produces untreated emissions 24 which include, among other things, NO_X and SO_X. NO_X trap 14 traps the NO_X present in exhaust gases 24 to prevent NO_X from being exhausted into the atmosphere, for example. Periodically, or as desired, NO_X trap 14 may be regenerated to remove NO_X trapped therein. SO_X, however, also has a tendency to become trapped within NO_X trap 14 and may eventually saturate NO_X trap 14 thus preventing additional NO_X from being retained or trapped within NO_X trap 14. Further, SO_X is generally not regenerated when a NO_X regeneration of NO_X trap 14 is performed. Therefore, SO_X may continue to accumulate within NO_X trap 14 and effectively poison NO_X trap 14 by rendering NO_X trap 14 ineffective at trapping NO_X. As mentioned above, system 10 is provided to purge SO_X trapped within NO_X trap 14 so that NO_X trap 14 may continue to trap NO_X therein.

Referring back to FIG. 1, a passageway 18 connects fuel reformer 12 with NO_X trap 14, and another passageway 20 connects engine 16 with NO_X trap 14. Fuel reformer 12 reforms (i.e., converts) hydrocarbon fuel into a reformate gas 22 that includes, among other things, hydrogen and carbon monoxide. Passageway 18 conducts the reformate gas 22 to NO_X trap 14 so that reformate gas 22 may be used to purge SO_X from NO_X trap 14 to prevent SO_X poisoning of NO_X trap 14 and thereby increase the efficiency of NO_X trap 14 in reducing NO_X emissions.

Fuel reformer 11 may be embodied as any type of fuel reformer, such as, for example, a catalytic fuel reformer, a thermal fuel reformer, a steam fuel reformer, or any other type of partial oxidation fuel reformer. Fuel reformer 12 may also be embodied as a plasma fuel reformer. A plasma fuel reformer uses plasma to convert a mixture of air and hydrocarbon fuel into a reformate gas rich in hydrogen and carbon monoxide. Systems including plasma fuel reformers are disclosed in U.S. Pat. No. 5,425,332 issued to Rabinovich et al.; U.S. Pat. No. 5,437,250 issued to Rabinovich et al.; U.S. Pat. No. 5,409,784 issued to Bromberg et al.; and U.S. Pat. No. 5,887,554 issued to Cohn, et al., the disclosures of which are hereby incorporated by reference.

As shown in FIG. 1, fuel reformer 12 and its associated components are under the control of a reformer controller 26. In particular, components such as temperature, pressure, or gas composition sensors (not shown), a fuel inlet assembly such as a fuel injector (not shown), and air inlet valve(s) (not shown) are each electrically coupled to the reformer controller 26. Moreover, a power supply 28 is electrically coupled to the reformer controller 26 via a signal line 30. Although signal line 30 is shown schematically as a single line, it should be appreciated that signal line 30, along with the signal line(s) associated with each of the other components of fuel reformer 12, may be configured as any type of signal carrying assembly which allows for the transmission of electrical signals in either one or both direction between the reformer controller 26 and the corresponding component. For example, any one or more of the signal lines may be embodied as a wiring harness having a number of signal lines which transmit electrical signals between the reformer controller 26 and the corresponding component. It should be appreciated that any number of other wiring configurations may also be used. For example, individual signal wires may be used, or a system utilizing a signal multiplexer may be used for the design of any one or more of the signal lines. Moreover, the signal lines may be integrated such that a single harness or system is utilized to electrically couple some or all of the components associated with fuel reformer 12 to reformer controller 26.

The reformer controller 26 is, in essence, the master computer responsible for interpreting electrical signals sent by sensors associated with the fuel reformer 12 and for activating electronically-controlled components associated with the fuel reformer 12 in order to control the fuel reformer 12. For example, the reformer controller 26 of the present disclosure is operable to, amongst many other things, actuate or shutdown the fuel reformer 12, determine the beginning and end of each injection cycle of fuel into the fuel reformer 12, calculate and control the amount and ratio of air and fuel to be introduced into the fuel reformer 12, determine the temperature of the fuel reformer 12, and determine the power level to supply to the fuel reformer 12.

To do so, the reformer controller 26 includes a number of electronic components commonly associated with electronic units which are utilized in the control of electromechanical systems. For example, the reformer controller 26 may include, amongst other components customarily included in such devices, a processor such as a microprocessor 32 and a memory device 34 such as a programmable read-only memory device (“PROM”) including erasable PROM's (EPROM's or EEPROM's). The memory device 34 is provided to store, amongst other things, instructions in the form of, for example, a software routine (or routines) which, when executed by the microprocessor 32, allows the reformer controller 26 to control operation of the fuel reformer 12.

The reformer controller 26 also includes an analog interface circuit (not shown). The analog interface circuit converts the output signals from the various fuel reformer sensors into a signal which is suitable for presentation to an input of the microprocessor 32. In particular, the analog interface circuit, by use of an analog-to-digital (A/D) converter (not shown) or the like, converts the analog signals generated by the sensors into a digital signal for use by the microprocessor 32. It should be appreciated that the A/D converter may be embodied as a discrete device or number of devices, or may be integrated into the microprocessor. It should also be appreciated that if any one or more of the sensors associated with the fuel reformer 12 generate a digital output signal, the analog interface circuit may be bypassed.

Similarly, the analog interface circuit converts signals from the microprocessor 32 into an output signal which is suitable for presentation to the electrically-controlled components associated with the fuel reformer 12 (e.g., the power supply 28). In particular, the analog interface circuit, by use of a digital-to-analog (D/A) converter (not shown) or the like, converts the digital signals generated by the microprocessor 32 into analog signals for use by the electronically-controlled components associated with the fuel reformer 12 such as the power supply 28. It should be appreciated that, similar to the A/D converter described above, the D/A converter may be embodied as a discrete device or number of devices, or may be integrated into the microprocessor 32. It should also be appreciated that if any one or more of the electronically-controlled components associated with the fuel reformer 12 operate on a digital input signal, the analog interface circuit may be bypassed.

Hence, the reformer controller 26 may be operated to control operation of the fuel reformer 12. In particular, the reformer controller 26 executes a routine including, amongst other things, a closed-loop control scheme in which the reformer controller 26 monitors outputs of the sensors associated with the fuel reformer 12 in order to control the inputs to the electronically-controlled components associated therewith. To do so, the reformer controller 26 communicates with the sensors associated with the fuel reformer in order to determine, amongst numerous other things, the amount, temperature, and/or pressure of air and/or fuel being supplied to the fuel reformer 12, the amount of oxygen in the reformate gas, the temperature of the reformate gas being produced thereby, and the composition of the reformate gas. Armed with this data, the reformer controller 26 performs numerous calculations each second, including looking up values in preprogrammed tables, in order to execute algorithms to perform such functions as determining when or how long the fuel reformer's fuel injector or other fuel input device is opened, controlling the power level input to the fuel reformer, controlling the amount of air advanced through the air inlet valve(s), etcetera.

As mentioned above, reformer controller 26 is electrically coupled to power supply 28 associated with the fuel reformer 12. As such, the reformer controller 26 communicates with the power supply 28 to selectively operate and shutdown the fuel reformer 12. Collectively, the fuel reformer 12 and the reformer controller 26 define a fuel reformer system 36 which, among other uses, may be used in the construction of an onboard system for a vehicle or a stationary power generator.

The engine 16, on the other hand, is under the control of an engine control unit 38. In particular, the engine control unit 38 is electrically coupled to a number of electronically-controlled components associated with the engine 16 (e.g., a fuel injector assembly, ignition assembly, etcetera) via a signal line 40. As with the signal lines associated with the fuel reformer 12, the signal line 40 may be any type of signal carrying connector including a wiring harness for carrying the electrical signals associated with numerous engine components.

The reformer controller 26 and the engine control unit 38 are in communication with one another. In particular, the reformer controller 26 is electrically coupled to the engine control unit 38 via a signal line 42.

The reformer controller 26 and the engine control unit 38 are shown as discrete components in FIG. 1. It should be appreciated, however, that the reformer controller 26 may be integrated into an engine control unit 38, as shown in FIG. 2. In such a way, a single hardware component may be utilized to control both the fuel reformer 12 and the engine 16.

Hence, the aforedescribed control scheme may be utilized to control operation of the fuel reformer 12 and the engine 16. In an exemplary embodiment, the aforedescribed control scheme includes a routine for desulfating NO_X trap 14, or in other words, regenerating NO_X trap 14 to remove SO_X trapped therein. As mentioned above, NO_X trap 14 is provided to trap NO_X contained within untreated exhaust gases 24 emitted from engine 16 so that generally NO_X-free treated emissions are exhausted out of NO_X trap 14. As desired, NO_X trap 14 also may be regenerated to remove NO_X trapped therein.

Also as described above, untreated exhaust gas 24 includes SO_X. Due to the nature of various NO_X traps, SO_X may be trapped therein as well, thus poisoning the NO_X trap 14 or otherwise reducing the trap's ability to trap additional amounts of NO_X. The present disclosure, therefore, provides a method and system 10 for desulfating NO_X trap 14, or, in other words, regenerating NO_X trap 14 to remove or purge SO_X which has been absorbed or trapped therein.

In particular, system 10 of the illustrative embodiments removes SO_X from NO_X trap 14 by both raising the temperature of NO_X trap 14 and introducing reformate gas 22 into NO_X trap 14 via passageway 18. As mentioned above, reformate gas 22 includes both hydrogen gas and carbon monoxide. Generally, absorbed SO_X may be purged from NO_X trap 14 by raising the NO_X trap 14 temperature in excess of about 650° C. while also post injecting additional hydrocarbon fuel to react with the absorbed SO_X. Reformate gas 22, as opposed to hydrocarbon fuel, reacts with the absorbed SO_X at a temperature lower than 650° C. to regenerate NO_X trap 14 and remove SO_X absorbed by NO_X trap 14 to allow NO_X trap 14 to more efficiently and effectively trap NO_X therein.

The temperature of NO_X trap 14 is raised by raising the temperature of untreated exhaust gases 24 advancing through NO_X trap 14 from engine 16. Particularly, one way to raise the temperature of exhaust gases 24 exiting engine 16 is to reduce an air-to-fuel ratio of an air/fuel mixture being introduced into engine 16. The air-to-fuel ratio of the air/fuel mixture is controlled by engine control unit 38. It is within the scope of this disclosure for the steps of raising the temperature of NO_X trap 14 and advancing reformate gas 22 into NO_X trap 14 to be performed contemporaneously or, in the alternative, for one step to be performed before the other and visa versa. Further, although the present system 10 desulfates NO_X trap 14 by both raising the temperature of NO_X trap 14 and advancing reformate fuel 22 into NO_X trap 14, it is within the scope of this disclosure to remove SO_X from NO_X trap 14 without the need to raise the temperature of NO_X trap 14 by advancing reformate fuel 22 into NO_X trap 14 without the need to raise the temperature of NO_X trap 14 at all.

Hence, the control scheme of the present disclosure includes a routine for selectively raising the temperature of the NO_X trap 14 to allow reformate gas containing hydrogen and carbon monoxide to be introduced into NO_X trap 14 to react with accumulated SO_X therein thereby removing the SO_X and regenerating the NO_X trap 14. The duration of the SO_X purge may be configured to ensure that all (or substantially all) of the accumulated SO_X has been purged from NO_X trap 14. In general, a SO_X regeneration of NO_X trap 14 is performed as a response to generation of a SO_X purge request. A SO_X purge request may be generated in response to any number of events.

One exemplary way to determine whether a SO_X purge (or desulfation) of NO_X trap 14 is to be performed is to purge the accumulated SO_X from NO_X trap 14 after regenerating the NO_X from within NO_X trap 14 a predetermined number of times. Such a control routine 100 is shown in FIG. 3 and begins with step 102 where reformer controller 26 determines whether a NO_X purge of NO_X trap 14 has been requested. Illustratively, a NO_X purge may be requested as a result of any number of factors including, time lapse since last NO_X purge, NO_X saturation of NO_X trap 14, etcetera.

If a NO_X purge has not been requested, control routine 100 loops back to the beginning and continues to determine whether a NO_X purge has been requested. However, if a NO_X purge request has been sensed by the reformer controller 26, control routine 100 advances to step 104 and a NO_X purge of NO_X trap 14 is performed. Illustratively, NO_X trap 14 may be purged raising the temperature of NO_X trap 14 to a predetermined temperature and advancing reformed fuel through NO_X trap 14, similar to SO_X regeneration of NO_X trap 14. However, the temperature required for NO_X regeneration of NO_X trap 14 is generally less than the temperature required for SO_X regeneration of NO_X trap 14. In other words, a NO_X purge may be performed at a lower temperature than a SO_X purge. It is within the scope of this disclosure for a NO_X purge to be accomplished by other means as well.

Once a NO_X purge has been performed, control routine 100 advances to step 106 to determine the number of NO_X purges performed (N_P) since the previous SO_X purge of NO_X trap 14. Once the number of NO_X purges performed (N_P) has been determined, control routine 100 advances to step 108. As shown in step 108, reformer controller 26 compares the number of NO_X purges performed (N_P) since the previous SO_X purge of NO_X trap 14 to a set point number (N). If the number of NO_X purges performed (N_P) is less than set point number (N), the control routine 100 loops back to step 102 to determine whether a NO_X purge has been requested. However, if the number of NO_X purges performed (N_P) is greater than or equal to the set point number of NO_X purges (N), a control signal is generated, and the control routine 100 advances to step 110.

In step 110, SO_X is purged from NO_X trap 14 in the manner described above. In particular, reformer controller 26 may generate a control signal on signal line 30 thereby instructing the fuel reformer 12 to advance reformate gas to NO_X trap 14 while also generating a control signal on signal line 42 instructing engine control unit 38 to operate the engine to cause a higher temperature exhaust gas 24 to be advanced from engine 16 to NO_X trap 14. As such, engine control unit 38 may generate a control signal on line 40 instructing engine 16 to decrease the air-to-fuel ratio of the air/fuel mixture introduced into engine 16 to raise the temperature of the untreated exhaust gas 24.

In another control routine 200, shown in FIG. 4, SO_X which accumulates within NO_X trap 14 is regularly purged at predetermined time intervals. In general, control routine 200 begins with step 202 in which the reformer controller 26 determines the time which has lapsed (T_L) since SO_X was last purged from NO_X trap 14, or more particularly, since fuel reformer 12 was last instructed to introduce reformate gas 22 into NO_X trap 14 to desulfate NO_X trap 14. Once controller 26 has determined the time which has lapsed (T_L), the control routine 200 advances to step 204. In step 204, controller 26 compares the time which has lapsed (T_L) to a predetermined set point time period (T). In particular, as described herein, a predetermined time period (T) between SO_X purge cycles may be established as desired.

If the amount of time lapsed (T_L) is less than the set point time period (T), the control routine 200 loops back to step 202 to continue monitoring the time which has lapsed since the last SO_X regeneration. It is within the scope of this disclosure for controller 26 to measure a predetermined amount of lapsed time from any step or reference point within control routine 200 or general operation of system 10. If, however, the amount of time lapsed (T_L) is greater than or equal to the set point time period (T), the control routine advances to step 206 to desulfate or purge NO_X trap 14. NO_X trap 14 is desulfated in the manner discussed above with respect to control routine 100.

In yet another illustrative control routine 300, shown in FIG. 5, NO_X trap 14 is desulfated based upon the accumulation of SO_X within NO_X trap 14. Control routine begins with step 302 in which reformer controller 26 determines the amount of SO_X (S_A) which has accumulated within NO_X trap 14. This may be accomplished through the use of a sensor or group of sensors associated with NO_X trap 14 and provided to indirectly measure or detect the amount of SO_X accumulated within NO_X trap 14. Such a sensor or sensors may be electrically coupled to reformer controller 26 via a signal line (not shown) so that controller 26 may scan or otherwise read the signal line in order to monitor output from the sensor(s). The output signals produced by the sensor(s) would be indicative of the amount of SO_X (S_A) within NO_X trap 14. Once the controller 26 has determined the amount of accumulated SO_X (S_A) within NO_X trap 14, the control routine 300 advances to step 304.

In step 304, controller 26 compares the sensed amount of SO_X (S_A) within NO_X trap 14 to a set point SO_X accumulation value (S). In particular, as described herein, a predetermined SO_X accumulation value (S), or set point, may be established which corresponds to a particular amount of SO_X accumulation within NO_X trap 14. If the amount of SO_X accumulation (S_A) within NO_X trap 14 is less than the set point SO_X accumulation value (S), the control routine 300 loops back to step 102 to continue monitoring the output from the sensor(s). However, if the SO_X accumulation (S_A) within NO_X trap 14 is equal to or greater than the set point SO_X accumulation value (S), a control signal is generated, and the control routine 300 advances to step 306. In step 306, reformer controller 26 operates in the manner described above to desulfate NO_X trap 14.

As described above, controller 26 operates to desulfate NO_X trap 14 by instructing fuel reformer 12 to advance reformate gas 22 into NO_X trap 14 and by instructing engine 16 to decrease the air-to-fuel ratio of the air/fuel mixture introduced into engine 16 to increase the temperature of untreated exhaust gas 24 for advancement into NO_X trap 14. Controller 26 operates in such a manner in response to various signals and/or events, such as after a predetermined number of NO_X purges, at predetermined time intervals, or in response to output from one or more sensors, for example. However, it is within the scope of this disclosure for controller 26 (with engine control unit 38) to desulfate NO_X trap 14 in response to various other signals and/or conditions.

Referring now to FIG. 6, an emission abatement system 410 is provided for use with engine 16 to remove or otherwise decrease the amount of emissions discharged into the atmosphere. System 410 includes a plurality of NO_X traps 414 positioned in a parallel flow arrangement for removing NO_X from exhaust gas discharged from engine 16. Each NO_X trap 414 traps NO_X when it is exposed to lean conditions (excess oxygen in exhaust gas) and releases and reduces trapped NO_X when exposed to rich conditions (depleted amount of oxygen in exhaust gas) during NO_X regeneration of the trap 414.

Sulfur substances (e.g., SO_X, sulfides, elemental sulfur) present in the exhaust gas have a tendency to become trapped by the NO_X traps 414. When this occurs, the ability of the trap 414 to trap and thus remove NO_X from the exhaust gas becomes degraded. Because of this potential for sulfur degradation (or sulfur poisoning) of the traps 414, system 410 is configured to desulfurize (i.e., remove sulfur substances from) each trap 410 from time to time.

System 410 is configured so that thermal damage to NO_X traps 414 due to excessive trap temperatures is avoided during trap desulfurization. Typically, it may take several minutes to desulfurize one trap 414. The trap 414 would be at risk for thermal damage due to uncontrolled trap temperature spikes if the trap 414 were to receive a flow of a desulfurization agent continuously until completion of desulfurization. Such a risk could possibly increase further in the event that oxgyen present in the exhaust gas were allowed (intentionally or unintentionally) to slip into the line containing the trap 414. To avoid such thermal damage, system 410 employs a “sequential cycling” method of desulfurizing the traps 414. In particular, once the system 410 determines that desulfurization is to take place, it causes a desulfurization agent to advance to the NO_X traps 414 in sequential order for a plurality of cycles and causes exhaust gas to advance to each trap 414 not receiving the desulfurization agent during the plurality of cycles.

During each cycle, each trap 414 receives the desulfurization agent for a predetermined period of time (e.g., a few seconds such as 5-15 seconds). The temperature of the trap 414 may begin to elevate during each period that it receives the desulfurization agent but it does not elevate beyond the thermal damage temperature threshhold because the predetermined period of time is not long enough to allow for such excessive temperature elevation. Moreover, when the trap 414 is not receiving the desulfurization agent, it is receiving a cooling flow of exhaust gas, thereby further promoting protection of trap 414 from thermal damage. Since the predetermined period of time that each trap 414 receives the desulfurization agent during each cycle is not long enough for complete desulfurization, system 410 cycles the desulfurization agent to the traps 414 for a plurality of cycles. As such, the cumulative time that each trap 414 receives the desulfurization agent during the plurality of cycles is sufficient to complete desulfurization of each trap 414. System 410 is thus able to control the temperature of traps 414 by use of this sequential cycling desulfurization method.

System 410 includes a controller 426 that is electrically coupled to a desulfurization agent supplier 428 via a supplier control line 430 and a valve arrangement 432 via a valve control line 434. Valve arrangement 432 is fluidly coupled to supplier 428 via a desulfurization agent line 436 to receive a desulfurization agent from supplier 428 and is fluidly coupled to engine 16 via an exhaust gas line 438 to receive exhaust gas from engine 16. Valve arrangement 432 is fluidly coupled to NO_X traps 414 via trap lines 440. Controller 426 may be separate from or integrated with the engine control unit used to control operation of engine 16. When it is integrated with the engine control unit, controller 426 is coupled to engine 16 via line 442.

Controller 426 comprises a processor 32 and a memory device 34 electrically coupled to processor 32. Memory device 34 has stored therein a plurality of instructions which, when executed by processor 32, causes processor 32 (i) to determine if desulfurization of the NO_X traps 414 is to be performed and to generate a desulfurization signal in response thereto, and (ii) to operate the desulfurization agent supplier 428 and the valve arrangement 432 to advance desulfurization agent from supplier 428 to the NO_X traps in sequential order for a plurality of cycles and exhaust gas from engine 16 to each NO_X trap not receiving the desulfurization agent during the plurality of cycles in response to the desulfurization signal so as to desulfurize the NO_X traps 414. Controller 426 operates supplier 428 and valve arrangement 432 by sending signals over lines 430 and 434, respectively. A control routine 500 for desulfurizing NO_X traps 414 is discussed in more detail below in connection with FIG. 8.

The desulfurization agent is used to desulfurize the NO_X traps 414. Each NO_X trap 414 has a catalyst component for catalyzing oxidation and reduction reactions and a storage component (made of, for example, a metal oxide such as barium oxide or potassium oxide) for storing NO_X. Both the catalyst component and the storage component are susceptible to poisoning by sulfur substances. The catalyst and storage components are desulfurized by use of the desulfurization agent according to control routine 500.

In an implementation of supplier 428, the desulfurization agent supplier 428 is a hydrocarbon supplier for injecting a desulfurization agent comprising hydrocarbons upstream of NO_X traps 414 for passage thereto. In one example, the hydrocarbon supplier is a diesel fuel supplier which supplies a desulfurization agent comprising diesel fuel for desulfurizing the traps 414.

In another implementation of supplier 428 the desulfurization agent supplier 428 is a fuel reformer assembly having fuel reformer 12 and power supply 28 (discussed above). The fuel reformer 12 produces a reformate gas including hydrogen (H₂) and carbon monoxide. The hydrogen and carbon monoxide act as the desulfurization agent. Compared to use of diesel fuel, use of reformate gas from fuel reformer 12 may enable achievement of lower NO_X trap desulfurization temperatures and may result in formation of less soot and less precious metal sulfides, less hydrocarbon slippage past traps 414, and a lower fuel penalty. Exemplarily, the fuel reformer 12 is a plasma fuel reformer.

Use of the sequential cycling method disclosed herein facilitates use of a desulfurization agent lambda value which is between about 0.4 and about 0.7 or between about 0.4 and about 0.5 (the lambda value is the air-to-fuel ratio of the desulfurization agent divided by the stoichiometric air-to-fuel ratio of the fuel used). Use of such a lambda value facilitates desulfurization of traps 414 at a lower desulfurization temperature than when a higher lambda value (e.g., 0.9 to 0.95) is used. The desulfurization agent can have such a lambda value when the desulfurization agent comprises, for example, diesel fuel.

Valve arrangement 432 may be configured in a variety of ways. For example, in one implementation of valve arrangement 432, a valve arrangement 432a is useful when there are only two NO_X traps 414a, 414b, as shown, for example, in FIG. 7. Valve arrangement 432a has a single valve 444 under the control of controller 426 to rotate in a valve housing 446 between a first position (shown in solid in FIG. 7) and a second position (shown in phantom in FIG. 7) to direct flow of the desulfurization agent and flow of the exhaust gas between the two NO_X traps 414a, 414b. In the first position, the valve 444 directs the flow of the desulfurization agent to the first NO_X trap 414a and the flow of the exhaust gas to the second NO_X trap 414b while blocking the flow of the desulfurization agent to the second NO_X trap 414b and the flow of the exhaust gas to the first NO_X trap 414a. In the second position, the valve 444 directs the flow of the desulfurization agent to the second NO_X trap 414b and the flow of the exhaust gas to the first NO_X trap 414a while blocking the flow of the desulfurization agent to the first NO_X trap 414a and the flow of the exhaust gas to the second NO_X trap 414b. As such, valve arrangement 432a alternates a flow of the desulfurization agent and a flow of the exhaust gas between the two NO_X traps 414a and 414b for the plurality of cycles in response to the desulfurization signal.

In another implementation of the valve arrangement 432, there are two valves associated with each trap 414, a desulfurization valve and an exhaust gas valve. Each desulfurization valve is under the control of controller 426 to selectively allow and block flow of the desulfurization agent to the associated trap 414. Each exhaust gas valve is under the control of controller 426 to selectively allow and block flow of the exhaust gas to the associated trap 414.

Referring to FIG. 8, a desulfurization control routine 500 is provided. At step 502, the controller 426 determines if desulfurization of the NO_X traps 414 is to be performed. A variety of methods can be used to determine whether to desulfurize the traps 414. In a first example, controller 426 uses a scheme in which desulfurization occurs once the NO_X traps 414 have been purged of NO_X a predetermined number of times since the last desulfurization event, similar to control routine 100. In a second example, the controller 426 uses a time-based scheme in which desulfurization occurs at predetermined intervals, similar to control routine 200. In a third example, the controller 426 uses a sulfur-accumulation-based scheme in which desulfurization occurs once accumulation of a predetermined amount of sulfur substances in NO_X traps 414 has reached a predetermined limit, similar to control routine 300. Such an accumulation limit can be detected indirectly by use of a NO_X sensor downstream from traps 414. In a fourth example, controller 426 uses information provided by a variety of sensors along with look-up tables stored in memory device 34.

If controller 426 determines that it is not time to desulfurize traps 414, control routine 500 loops back to the beginning of the routine. If controller 426 determines that desulfurization is to take place, it generates the desulfurization signal to initiate desulfurization and control routine 500 advances to step 504.

At step 504, the controller sets N (representative of a particular NO_X trap) to equal 1 to start the first cycle. After this, the control routine 500 advances to step 506.

At step 506, the controller 426 operates supplier 428 and valve arrangement 432 to cause desulfurization agent to advance to the first NO_X trap while exhaust gas is advanced to all the other NO_X trap(s) 414. The controller 426 keeps track of the amount of time that the first NO_X trap receives the desulfurization agent. At step 508, the controller 426 determines whether this time is less than a predetermined period of time (T_D). If the answer is yes, the controller 426 causes desulfurization of the first trap 414 to continue. If the answer is no (i.e., T_D has been reached), the control routine 500 advances to step 510.

At step 510, the controller 426 determines whether all NO_X traps have been desulfurized for the predetermined period of time so as to complete the first cycle. If the answer is no, the control routine 500 advances first to step 512 where the controller 426 adds one increment to N and then advances back to step 506 where the controller 426 causes desulfurization of the second NO_X trap 414 for the predetermined period of time (T_D). The control routine 500 continues to loop in this manner until each trap 414 has been desulfurized for the predetermined period of time (T_D) to thereby complete the first cycle. After completing the first cycle, the control routine advances to step 514.

At step 514, the controller 426 determines whether to repeat the cycle to sequentially desulfurize the traps 414, each for the predetermined period of time (T_D). In one example, this decision whether to repeat the cycle is based on whether a the traps 414 have been desulfurized for a predetermined number of cycles (i.e., whether a predetermined number of cycles has been reached). In another example, this decision is based on whether the cumulative amount of time elapsed since generation of the desulfurization signal has reached a predetermined time limit (e.g., several minutes such as 10 to 15 minutes). In another example, this decision is based on the amount of sulfur substance stored in traps 414, which can be indirectly determined by sensing NO_X at a location downstream from traps 414. If controller 426 determines that the cycle is to be repeated, control routine 500 returns to step 504 where N is set to equal one again to thereby begin a new cycle of sequential desulfurization of traps 414. If the controller 426 determines that cycling is to cease, control routine 500 returns to the beginning of the routine 500 due to completion of desulfurization of the traps 414.

It is within the scope of this disclosure to pre-heat the NO_X traps 414 by use of one or more heaters (not shown) to raise the temperature of the NO_X traps to a predetermined desulfurization temperature conducive to their desulfurization. In one example, there is only one heater placed upstream from the NO_X traps to heat all the NO_X traps. In another example, there is a heater placed in each trap line 440 upstream from the associated trap 414. Each heater may or may not be under the control of controller 426. Each heater may be a diesel oxidation catalyst, a fuel-fired burner, an electric heater, or the like. When a plasma fuel reformer is used as the supplier 428 to produce the desulfurization agent, pre-heating of the traps 414 by one or more heaters may not be needed.

While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only the illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.

There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. It will be noted that alternative embodiments of each of the systems of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A method of desulfating a NOX trap including the steps of:

operating a fuel reformer so as to produce a reformate gas comprising hydrogen and carbon monoxide,

advancing the reformate gas into the NOX trap to react the hydrogen and carbon monoxide with SOX trapped on the NOX trap to remove SOX from the NOX trap, and

raising the temperature within the NOX trap during the advancing step.

2. The method of claim 1, wherein the step of raising the temperature within the NOX trap includes raising the temperature of exhaust gases advancing through the NOX trap from an internal combustion engine.

3. The method of claim 2, wherein the step of raising the temperature further includes reducing an air-to-fuel ratio of an air/fuel mixture being introduced into the internal combustion engine.

4. The method of claim 1, wherein raising the temperature further includes raising the NOX trap to a temperature less than about 650° C.

5. The method of claim 1, further including the step of determining if the NOX trap is to be purged of SOX and generating a purge-SOX signal in response thereto, and wherein the advancing step further includes advancing the reformate gas into the NOX trap to remove SOX from the NOX trap in response to generation of the purge-SOX signal.

6. The method of claim 5, wherein the determining step comprises determining if a predetermined period of time has elapsed since the NOX trap was last purged of SOX and generating a time-lapsed control signal in response thereto, and the advancing step further includes advancing the reformate gas into the NOX trap to remove SOX from the NOX trap in response to generation of the time-lapsed control signal.

7. The method of claim 5, wherein the determining step comprises sensing the amount of SOX within the NOX trap.

8. The method of claim 7, wherein:

the sensing step includes the step of generating a trap-saturated control signal when the amount of SOX within the NOX trap reaches a predetermined accumulation level, and

the advancing step includes advancing the reformate gas into the NOX trap to remove the SOX within the NOX trap in response to the generation of the trap-saturated control signal.

9. A method of desulfurizing a plurality of NOX traps positioned in a parallel flow arrangement, the method comprising the steps of:

determining if desulfurization of the NOX traps is to be performed and generating a desulfurization signal in response thereto, and

advancing, in response to the desulfurization signal, (i) a desulfurization agent to the NOX traps in sequential order for a plurality of cycles and (ii) internal combustion engine exhaust gas to each NOX trap not receiving the desulfurization agent during the plurality of cycles.

10. The method of claim 9, wherein the advancing step comprises blocking flow of the exhaust gas to whichever NOX trap is receiving the desulfurization agent.

11. The method of claim 9, wherein the advancing step comprises advancing the desulfurization agent to each NOX trap for a predetermined period of time during each cycle.

12. The method of claim 9, wherein the advancing step comprises operating a valve arrangement so as to control flow of the desulfurization agent and flow of the exhaust gas between the NOX traps for the plurality of cycles.

13. The method of claim 9, wherein:

each NOX trap comprises a catalyst component for catalyzing oxidation and reduction reactions and a storage component for storing NOX, and

the advancing step comprises desulfurizing the catalyst component and the storage component of each NOX trap.

14. The method of claim 9, wherein the advancing step comprises (i) operating a plasma fuel reformer so as to produce a reformate gas comprising hydrogen and carbon monoxide and (ii) advancing the reformate gas to the NOX traps in sequential order for the plurality of cycles.

15. The method of claim 9, wherein the advancing step comprises advancing diesel fuel to the NOX traps in sequential order for the plurality of cycles.

16. A method of desulfurizing a plurality of NOX traps positioned in a parallel flow arrangement, the method comprising the steps of:

determining if desulfurization of the NOX traps is to be performed and generating a desulfurization signal in response thereto, and

advancing a desulfurization agent to the NOX traps in sequential order for a plurality of cycles in response to the desulfurization signal.

17. The method of claim 16, wherein the plurality of NOX traps comprise first and second NOX traps, and the advancing step comprises alternating a flow of the desulfurization agent and a flow of exhaust gas between the first and second NOX traps for the plurality of cycles in response to the desulfurization signal.

18. The method of claim 17, wherein the advancing step comprises moving a valve in response to the desulfurization signal a plurality of times between (i) a first position directing the flow of the desulfurization agent to the first NOX trap and the flow of the exhaust gas to the second NOX trap, and (ii) a second position directing the flow of the desulfurization agent to the second NOX trap and the flow of the exhaust gas to the first NOX trap.

19. The method of claim 16, wherein the advancing step comprises cooling each NOX trap not receiving the desulfurization agent with exhaust gas from an internal combustion engine during the plurality of cycles.

20. The method of claim 19, wherein the advancing step comprises blocking flow of the exhaust gas to whichever NOX trap is receiving the desulfurization agent.

21. The method of claim 16, wherein the advancing step comprises (i) operating a fuel reformer so as to produce a reformate gas comprising hydrogen and carbon monoxide and (ii) advancing the reformate gas to the NOX traps in sequential order for the plurality of cycles in response to the desulfurization signal.

22. The method of claim 16, wherein the advancing step comprises advancing diesel fuel to the NOX traps in sequential order for the plurality of cycles in response to the desulfurization signal.

23. The method of claim 16, wherein the advancing step comprises advancing a desulfurization agent comprising diesel fuel and having a lambda value between about 0.4 and about 0.7 to the NOX traps in sequential order for the plurality of cycles.

24. An emission abatement system, comprising:

a plurality of NOX traps positioned in a parallel flow arrangement,

a desulfurization agent supplier for supplying a desulfurization agent,

a valve arrangement for directing flow of the desulfurization agent and internal combustion engine exhaust gas between the NOX traps, and

a controller electrically coupled to the desulfurization agent supplier and the valve arrangement, the controller comprising a processor and a memory device electrically coupled to the processor, the memory device having stored therein a plurality of instructions which, when executed by the processor, causes the processor to:

determine if desulfurization of the NOX traps is to be performed and generate a desulfurization signal in response thereto, and

operate, in response to the desulfurization signal, the desulfurization agent supplier and the valve arrangement to advance (i) the desulfurization agent to the NOX traps in sequential order for a plurality of cycles and (ii) the exhaust gas to each NOX trap not receiving the desulfurization agent during the plurality of cycles.

25. The emission abatement system of claim 24, wherein:

the plurality of NOX traps comprise two NOX traps, and

the plurality of instructions, when executed by the processor, further cause the processor to operate the valve arrangement to alternate a flow of the desulfurization agent and a flow of the exhaust gas between the two NOX traps for the plurality of cycles in response to the desulfurization signal.

26. The emission abatement system of claim 24, wherein the plurality of instructions, when executed by the processor, further cause the processor to operate the valve arrangement so as to block flow of exhaust gas to whichever NOX trap is receiving the desulfurization agent.

27. The emission abatement system of claim 24, wherein the plurality of instructions, when executed by the processor, further cause the processor to operate the desulfurization agent supplier and the valve arrangement to advance the desulfurization agent to each NOX trap for a predetermined period of time during each cycle.

28. The emission abatement system of claim 24, wherein:

the desulfurization agent supplier is a plasma fuel reformer, and

the plurality of instructions, when executed by the processor, further cause the processor to operate the plasma fuel reformer and the valve arrangement so as to advance a reformate gas produced by the plasma fuel reformer to the NOX traps in sequential order for the plurality of cycles.

29. The emission abatement system of claim 24, wherein:

the desulfurization agent supplier is a hydrocarbon supplier, and

the plurality of instructions, when executed by the processor, further cause the processor to operate the hydrocarbon supplier and the valve arrangement so as to advance hydrocarbons from the hydrocarbon supplier to the NOX traps in sequential order for the plurality of cycles.