Abstract:
A system for controlled regeneration of a lean NO x  trap for an internal combustion engine. The system may include regenerating one trap or a portion of a lean NO x  trap while using another trap or portion of the lean NO x  trap for an exhaust, and then interchanging operations. The portions may be individual structures or of one structure. The trap may be a rotating element that is regenerated in part at a time. There may be valves that direct the exhaust gas through one trap and regeneration gas through another trap and vice versa. Also, an exhaust system with regeneration may include temperature, pressure, NO x  and differential pressure sensors. A processor may be connected to the sensors. There may be emission sampling lines connected to different parts of the system and to a collector to take, store, detect and analyze samples. A processor may be connected to the collector.

Description:
BACKGROUND  
       [0001]     The invention pertains to engine exhaust systems and particularly to pollutant control from exhaust systems. More particularly, the invention pertains to regeneration of pollutant reduction systems of exhaust systems.  
       SUMMARY  
       [0002]     The invention provides controlled regeneration of a lean NO x  trap for an engine exhaust system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0003]      FIGS. 1   a  and  1   b  show a dual trap catalytic system;  
         [0004]      FIG. 2  is a diagram of a lean NO x  regenerative system with instrumentation;  
         [0005]      FIG. 3  is a graph of injection rate control;  
         [0006]      FIG. 4  is a graph showing management of exhaust temperature;  
         [0007]      FIG. 5  is a graph showing an example of a deterioration rate of a catalyst;  
         [0008]      FIG. 6   a  is a diagram of a chemical process for trapping;  
         [0009]      FIG. 6   b  is a diagram of a regeneration using a rich, high temperature fuel mixture;  
         [0010]      FIG. 7   a  shows a device that may be placed in an exhaust stream of a system;  
         [0011]      FIG. 7   b  shows a regeneration storage device which may be moved to a side stream with a low flow rate, high temperature and low oxygen; and  
         [0012]      FIGS. 8, 9  and  10  reveal various continuously rotating lean NO x  trap assemblies having an absorption element. 
     
    
     DESCRIPTION  
       [0013]     Diesel engines and lean burn gasoline engines may offer thirty to fifty percent and ten to fifteen percent fuel economy benefit respectively compared to conventional gasoline engines in automobiles. However, a lean NO x  trap (LNT) system may be needed to reduce NO x  emissions. A conventional, full flow lean NO x  trap system representing the state of the art may reduce NO x  but has several disadvantages, which include a high fuel penalty because the temperature of the full exhaust stream needs to be raised periodically; the catalyst loading is tied to NO x  storage capacity; high desulfation temperatures of the LNT may affect the durability to the catalyst; and the efficiency is affected because NO x  from downstream material has less chance to encounter a catalyst. A controlled regeneration lean NO x  trap system may overcome these problems.  
         [0014]     The present system may solve such problems by implementing several principles. They are to separate the catalysis and NO x  storage functions, and to conduct regeneration of storage medium using a separate, controlled stream of gases. There may be many physical implementations of these principles.  
         [0015]     Under “normal” operating conditions, an exhaust may flow over an oxidation catalyst which oxidizes NO to NO 2  and then over an absorption system consisting of adsorption material such as Ca or BaCO 3 . When the adsorption system is “saturated” and the adsorption efficiency falls, flow may be diverted to a much smaller adsorption canister. NO x  sensor signals together with appropriate computation may be used to trigger the diversion. While the main engine exhaust flows through the smaller system, the primary system may be regenerated using a flow stream of controlled temperature, oxygen and CO/HC concentration. When the primary system is regenerated to a pre-set level, the flow may be restored to normal conditions and the smaller system may be regenerated. The ratio of storage to regeneration times may determine the size ratio of the two systems. Alternatively, a rotating adsorption element may be used. Adsorption and regeneration functions may be carried on continuously as the element rotates and maintain adsorption efficiency. Desorbed NO 2  may be reduced to N 2  in a downstream three way catalyst.  
         [0016]      FIG. 1   a  shows a catalytic system  80  having a dual trap  30 . Dual trap  30  may include a primary lean NO x  trap (P-LNT)  82  and a secondary lean NO x  trap (S-LNT)  83 . An exhaust pipe  78  may connect a catalytic converter  81  (O x C) to an exhaust manifold of an engine  11  ( FIG. 2 ). An exhaust  79  may enter the catalytic converter  81  (O x C) having an oxidation catalyst for converting NO to NO 2 . The catalyst material may be a precious metal such as Pt or a comparable material. The exhaust  79  may go from converter  81  to the primary lean NO x  trap (P-LNT)  82  which may be sized for NO x  storage capacity. The base material of trap  82  may contain or may be a metal such as barium or calcium. Alternatively, the exhaust  79  may go from converter  81  to the secondary lean NO x  trap (S-LNT)  83 , which may be sized for a short duration while the primary trap  82  is being regenerated. A two-way valve  91  may direct exhaust gas  79  in one of two directions, that is, to the primary trap  82  or to the secondary trap  83 , depending on whether the primary lean NO x  trap  82  is being generated or not. A burner (B)  84  may be used for generating a low flow rate of gas  95  at a high temperature and a zero oxygen for regeneration of the lean NO x  trap  82  or  83 . Burner  84  may heat an exhaust gas or provide another heated gas for regeneration. One trap may be regenerated while the other is functioning as a trap. An output of a trap  82  or  83  may proceed through a three way catalytic (TWC) device  85  having a precious metal catalyst such as Pt or the like.  
         [0017]     A two-way valve  92  may direct the low flow rate of gas  95  for regeneration to trap  82  or trap  83 . A two-way valve  93  may direct an output of trap  82  to an exhaust pipe  96  if it is an exhaust gas  79  or to the TWC device  85  if it is a regenerative gas  95 . A two-way valve  94  may direct an output of trap  83  to an exhaust pipe  96  if it is an exhaust gas  79  or to the TWC device  85  if it is a regenerative gas  95 . Valves  91 - 94  may be in one of two positions, A and B, or in one of more than two positions (i.e., a valve having a variable opening and closure). If the valves  91 - 94  are moved toward the A position, the P-LNT device  82  may be used as an exhaust trap and the S-LNT device  83  may be in regeneration. If the valves  91 - 94  are moved toward the B position, the P-LNT device  82  may be in regeneration and the S-LNT device  83  may be used as an exhaust trap. The valves  91 - 94  may have actuators connected to a processor  90 , as shown in  FIG. 1   b , (and/or an ECU (engine control unit)) which determines when the valves  91 - 94  should be in position A or B, or in between, and when burner  84  should be functioning. Such actuation may be determined according to the regenerative need of devices  82  and  83 , and possibly other factors.  
         [0018]     The dual trap system  80  of  FIGS. 1   a  and  1   b  may have instrumentation at various places of the system as shown in  FIG. 1   b . There may be temperature sensors  131  and  132  at the input and output, respectively, of converter  81 . There may be pressure sensors  141  and  142  at the input and output, respectively, of converter  81 . There may be sampling lines  161  and  162  at the input and output, respectively, of converter  81 . There may be an NO X  sensor  152  at the output of converter  81 . There may be a temperature sensor  133 , a pressure sensor  143 , an NO x  sensor  153  and a sampling line  163  at the output of P-LNT  82 . There may be a temperature sensor  134 , a pressure sensor  144 , an NO x  sensor  154  and a sampling line  164  at the output of S-LNT  83 . There may be similar sensors immediately positioned at the inputs of P-LNT and S-LNT; however, the sensors  132 ,  142 ,  152  and  162  at the output of converter  81  may be sufficient in lieu of the LNT input sensors.  
         [0019]     There may a temperature sensor  135 , pressure sensor  145  and sampling line  165  at the output of TWC  85  or a filter  85 . If a filter  85  is in place for regular exhaust  79  to go through it, then valves  93  and  94  may be appropriately switched to effect a flow of gas  79  through the filter. Filter  85  may be regenerated, for instance, with a sufficiently hot gas ( 95  or  79 ). The filter  85  may, for example, be a particulate matter filter.  
         [0020]     There may be a differential pressure sensor pair  146  and  147  at the input and output, respectively, of TWC or filter  85 . There may also be a temperature sensor  138  and a pressure sensor  148  at the output of burner  84 . The sensors may be connected to the processor  90 . The sensors and sampling lines may be upstream or downstream of the respective proximate valves. The sampling lines may be connected to a collection and detection apparatus which may be a part of processor  90 . The connections of the sensors and sampling lines to the processor  90  are not shown in  FIG. 1   b . There may be additional sensors and sampling lines situated in system  80 . Other kinds of sensors may be placed in system  80 .  
         [0021]      FIG. 2  shows an example of instrumentation-equipped exhaust catalyst system  10 . For many engines, such as diesel engines, the most significant pollutants to control may be particulate matter (PM), oxides of nitrogen (NO x ), and sulfur (SO x ). An engine  11  may output an exhaust  12  to a pre-catalyst device  13  via a manifold  97  and an exhaust pipe  14 . The pre-catalyst device  13  may be primarily an oxidation catalyst. The pre-catalyst  13  may be used to raise the temperature of the exhaust  12  for a fast warm-up and to improve the effectiveness of a catalytic system downstream when the engine exhaust temperatures are too low. The exhaust  12  may proceed on to an underbody NO x  adsorber catalyst (NAC) device  15  via an exhaust pipe  16 .  
         [0022]     The NAC may be primarily for adsorbing and storing NO x  in the form of nitrates. For instance, a diesel exhaust may tend to have excess oxygen. Therefore, NO x  might not be directly reducible to N 2 . The NO x  may be stored for a short period of time (for about a 60 second capacity). A very short period (i.e., about 2 to 5 seconds) of a very rich fuel air mixture operation may be conducted to get the exhaust stream down to a near zero oxygen concentration. The temperature may also be raised to a desirable window. Under these conditions, NO x  may react with CO and HC in the exhaust to yield N 2 , CO 2  and H 2 O. A base and precious metal catalyst may be used.  
         [0023]     The exhaust  12  may go from an NAC  15  to a catalytic diesel particulate filter  17  via an exhaust pipe  18 . This filter may provide physical filtration of the exhaust  12  to trap particulates. It may be composed of a precious metal. Whenever the temperature window is appropriate, then oxidation of the trapped particulate matter may take place. The exhaust  12  may exit the system  10  via an exhaust pipe  19 .  
         [0024]     In addition to the 60/2-5 second lean/rich swing for NO x  adsorption/desorption reduction, there may be other “forced” events. They include desulfurization and PM burn-off. The NO x  adsorption sites may get saturated with SO x . So, periodically, the SO x  should be driven off which may require a much higher temperature than needed for NO x  desorption. As to PM burn-off, there may be a forced burn-off if driving conditions (such as long periods of low speed or urban operation) result in excessive PM accumulation. The accumulation period may be several hours depending on the duty cycle of operation. The clean up may be several minutes (about 10). Higher temperatures and a reasonable oxygen level may be required.  
         [0025]     It may be seen that the catalytic system  10  may involve a complex chemical reaction process. This process may utilize monitoring of flows, temperatures, pressures, and pollutants by sensors connected to a processor or computer  20 . The sensors may be situated at various places in the catalytic exhaust system  10 , and be used to detect the capacity saturation point, the need to raise the exhaust temperature, the end of the clean up, and the restoration of normal operation.  
         [0026]     A temperature sensor  21  and pressure sensor  22  may be situated in exhaust pipe  14  and be connected to a computer or processor  20 . Situated in exhaust pipe  16  may be a temperature sensor  23  and a pressure sensor  24  connected to processor  20 . In exhaust pipe  18  may be a temperature sensor  25  and a pressure sensor  26 . A temperature sensor  27  and pressure sensor  28  may be situated in the exhaust pipe  19 . A differential pressure sensor  29  may be connected to exhaust pipe  18  and exhaust pipe  19  to detect the pressure difference between exhaust pipes  18  and  19 . This difference determination may be transmitted to the processor  20 . An NO x  sensor  31  may be situated in the exhaust pipe  16  and connected to processor  20 . In exhaust pipe  18  may be an NO x  sensor  32  which may be connected to processor  20 . Processor  20  may be connected to an engine control unit (ECU)  65  at engine  11 .  
         [0027]     There also may be several emission sampling lines  41 ,  42 ,  43  and  44  from exhaust pipes  14 ,  16 ,  18  and  19 , respectively, to a collector  45  of samples for testing and evaluation. Collector  45  may be connected to processor  20 . There may be additional sensors  46 ,  47 ,  48  and  49  in exhaust pipes or lines  14 ,  16 ,  18  and  19 , respectively, for testing of various parameters as desired or needed of the exhaust system  10 . The collector  45  may be connected to processor  20 .  
         [0028]     Fuel injection systems may be designed to provide injection events, such as the pre-event  51 , pilot event  52 , main event  53 , after event  54  and post event  55 , in that order of time, as shown in the graph of injection rate control in  FIG. 3 , which shows injected fuel versus crankshaft position. After-injection and post-injection events  54  and  55  do not contribute to the power developed by the engine, and may be used judiciously to simply heat the exhaust and use up excess oxygen. The pre-catalyst may be a significant part of the present process because all of the combustion does not take place in the cylinder.  FIG. 4  is a graph  65  showing management of exhaust temperature. Line  56  is a graphing of percent of total torque versus percent of engine speed. The upper right time line shows a main injection event  57  near top dead center (TDC) and a post injection event  58  somewhat between TDC and bottom dead center (BDC). This time line corresponds to a normal combustion plus the post injection area above line  56  in the graph  65 . The lower right time line shows the main injection event  57  near TDC and a first post injection event  59  just right after main event  57 , respectively, plus a second post injection event  58 . This time line corresponds to a normal combustion plus two times the post injection area below line  56  in the graph  65 .  
         [0029]     In some cases, when the temperature during expansion is very low (as under light load conditions), the post injection fuel may go out as raw fuel and become difficult to manage using the pre-catalyst  13 . Under such conditions, two post injections  59  and  58  may be used—one to raise temperatures early in the expansion stroke and the second to raise it further for use in downstream catalyst processes. There could be an impact on the fuel economy of the engine.  
         [0030]     One aspect of the present system may be based on information from process control  20 . Normally in a catalytic flow system, the effectiveness of a catalyst may be reduced exponentially in the direction of flow along the length of the catalyst as shown in  FIG. 5 .  FIG. 5  is a graph  66  showing an example of a deterioration rate of a catalyst. The graph shows a percent of absorption sites used up versus the percent of the total length of the catalyst device. Curves  61 ,  62 ,  63  and  64  are plots of sites used versus catalyst length for different time periods with increasing time as shown by line  70  in the graph.  
         [0031]     The catalytic and storage operations may be different. Downstream desorption may see less catalyst and thus have low NO x  conversion efficiency. If the lean NO x  trap (LNT) and the catalyst are separated in a conventional full-flow system, the catalyst may be needed upstream for oxidation and downstream for reduction. The catalyst (Pt) and storage material (Ba 2 CO 3 ) may be mixed in conventional, full flow LNT systems. There may be issues about “mixed” full flow systems, which include raising the temperature of the full exhaust system, tying storage capacity to the high cost Pt, and high desulfication temperatures causing catalyst deterioration.  
         [0032]      FIG. 6   a  is a diagram of a chemical process for trapping (lean fuel mixture). NO and O 2  may join in with NO 2  of the Pt catalyst  67  which may result in NO 3  going to the trap  68 .  FIG. 6   b  is a diagram of a regeneration using a rich, high temperature fuel mixture. There may be fuel that is added to the collected NO 3  in a trap  69 . A fuel from a rich exhaust may be added to the NO 3  thereby resulting in a combination going from the trap  69  towards the Pt catalyst  71 . In the case of the latter action, the hot NO 3  expunged from the trap may go to the catalyst  71 . Here, the NO 3  may shed N 2  and take on CO to form NO in the catalyst.  
         [0033]     The catalytic and storage processes and materials may be separated. Multiple physical configurations are possible.  FIG. 7   a  shows a device  72  that may be placed in the exhaust stream of a system. Device  72  may operate as a trap in normal lean operation and correspond to a process of  FIG. 6   a . The Pt in a catalyst section  73  may be sized for NO—NO 2  conversion efficiency at a full exhaust flow rate. The material in section  73  may be some other comparable material. The trapping material Ba 2 CO 3  in the trapping section  74  may be sized for an optimum storage capacity/efficiency/space trade-off.  FIG. 7   b  shows a regeneration storage device which may be moved to a side stream with a low flow rate, high temperature and low oxygen. A section  76  may contain trapping material Ba 2 NO 3 . The NO 3  from the regenerated trap section  76  may go to a catalyst section  77  for conversion to NO. The amount of Pt needed in section  77  may be small because of a low flow rate. The catalyst material may be a comparable material in place of Pt.  
         [0034]      FIG. 8  reveals a continuously rotating lean NO trap (LNT) of an assembly  40  having an absorption NO x  element  109  in a section  101 . Section  102  may have an oxidation catalyst (O x C)  104  and a burner (B)  105 . The burner  105  may provide a controlled stream of hot, zero oxygen, controlled CO/HC concentration gases, i.e., regeneration gases. End view  106  reveals the sectors of O x C  104  and B  105 . A section  103  has a sector of three way catalyst (TWC)  108  using flow from the burner  105 , as shown by end view  107 , going through a portion of the trap element for regeneration of that portion, to the TWC  108 . The trap  109  may rotate so that all portions of it may eventually be regenerated.  
         [0035]      FIG. 9  shows a continuously rotating lean NO x  trap (LNT) assembly  50  having an adsorption element  114  in section  111 . Section  112  may have a sector which is a burner (B)  115  and an oxidation catalyst (O x C)  116 , as shown by end view  117 . Section  113  may have a sector which is a three way catalyst (TWC)  119  and a sector of the absorption element  114 , as shown by end view  118 . The burner  115  may provide a controlled stream of hot, zero oxygen, controlled CO/HC concentration gases. A balance between the regeneration and rotation may maintain the required adsorption efficiency of the main lean NO x  trap  50 .  
         [0036]      FIG. 10  shows a continuously rotating lean NO x  trap (LNT)  127  assembly  60  having sections  121 ,  122  and  123 . End view  124  of section  122  shows a sector of a burner (B)  126  and a remaining sector  127  of the adsorption trap. End view  125  of section  123  shows a sector of a three way catalyst (TWC)  128  and a remaining sector  127  of the adsorption trap.  
         [0037]     In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.  
         [0038]     Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.