US20070144149A1

US20070144149A1 - Controlled regeneration system

Info

Publication number: US20070144149A1
Application number: US11/306,438
Authority: US
Inventors: Soumitri Kolavennu; Syed Shahed
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 2005-12-28
Filing date: 2005-12-28
Publication date: 2007-06-28
Also published as: WO2007078932A3; JP2009522489A; WO2007078932A2; CN101375029A; EP1969209A2

Abstract

A system for controlled regeneration of a lean NO_xtrap for an internal combustion engine. The system may include regenerating one trap or a portion of a lean NO_xtrap while using another trap or portion of the lean NO_xtrap 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_xand 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

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

The invention provides controlled regeneration of a lean NO_xtrap for an engine exhaust system.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 a and 1 b show a dual trap catalytic system;
FIG. 2 is a diagram of a lean NO_xregenerative system with instrumentation;
FIG. 3 is a graph of injection rate control;
FIG. 4 is a graph showing management of exhaust temperature;
FIG. 5 is a graph showing an example of a deterioration rate of a catalyst;
FIG. 6 a is a diagram of a chemical process for trapping;
FIG. 6 b is a diagram of a regeneration using a rich, high temperature fuel mixture;
FIG. 7 a shows a device that may be placed in an exhaust stream of a system;
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
FIGS. 8, 9 and 10 reveal various continuously rotating lean NO_xtrap assemblies having an absorption element.

DESCRIPTION

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_xtrap (LNT) system may be needed to reduce NO_xemissions. A conventional, full flow lean NO_xtrap system representing the state of the art may reduce NO_xbut 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_xstorage capacity; high desulfation temperatures of the LNT may affect the durability to the catalyst; and the efficiency is affected because NO_xfrom downstream material has less chance to encounter a catalyst. A controlled regeneration lean NO_xtrap system may overcome these problems.
The present system may solve such problems by implementing several principles. They are to separate the catalysis and NO_xstorage functions, and to conduct regeneration of storage medium using a separate, controlled stream of gases. There may be many physical implementations of these principles.
Under “normal” operating conditions, an exhaust may flow over an oxidation catalyst which oxidizes NO to NO₂and then over an absorption system consisting of adsorption material such as Ca or BaCO₃. When the adsorption system is “saturated” and the adsorption efficiency falls, flow may be diverted to a much smaller adsorption canister. NO_xsensor 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 NO₂may be reduced to N₂in a downstream three way catalyst.
FIG. 1 a shows a catalytic system 80 having a dual trap 30. Dual trap 30 may include a primary lean NO_xtrap (P-LNT) 82 and a secondary lean NO_xtrap (S-LNT) 83. An exhaust pipe 78 may connect a catalytic converter 81 (O_xC) to an exhaust manifold of an engine 11 (FIG. 2). An exhaust 79 may enter the catalytic converter 81 (O_xC) having an oxidation catalyst for converting NO to NO₂. 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_xtrap (P-LNT) 82 which may be sized for NO_xstorage 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_xtrap (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_xtrap 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_xtrap 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.
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.
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_Xsensor 152 at the output of converter 81. There may be a temperature sensor 133, a pressure sensor 143, an NO_xsensor 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_xsensor 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.
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.
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.
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_xadsorber catalyst (NAC) device 15 via an exhaust pipe 16.
The NAC may be primarily for adsorbing and storing NO_xin the form of nitrates. For instance, a diesel exhaust may tend to have excess oxygen. Therefore, NO_xmight not be directly reducible to N₂. The NO_xmay 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_xmay react with CO and HC in the exhaust to yield N₂, CO₂and H₂O. A base and precious metal catalyst may be used.
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.
In addition to the 60/2-5 second lean/rich swing for NO_xadsorption/desorption reduction, there may be other “forced” events. They include desulfurization and PM burn-off. The NO_xadsorption sites may get saturated with SO_x. So, periodically, the SO_xshould be driven off which may require a much higher temperature than needed for NO_xdesorption. 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.
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.
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_xsensor 31 may be situated in the exhaust pipe 16 and connected to processor 20. In exhaust pipe 18 may be an NO_xsensor 32 which may be connected to processor 20. Processor 20 may be connected to an engine control unit (ECU) 65 at engine 11.
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.
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.
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.
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.
The catalytic and storage operations may be different. Downstream desorption may see less catalyst and thus have low NO_xconversion efficiency. If the lean NO_xtrap (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 (Ba₂CO₃) 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.
FIG. 6 a is a diagram of a chemical process for trapping (lean fuel mixture). NO and O₂may join in with NO₂of the Pt catalyst 67 which may result in NO₃going 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 NO₃in a trap 69. A fuel from a rich exhaust may be added to the NO₃thereby resulting in a combination going from the trap 69 towards the Pt catalyst 71. In the case of the latter action, the hot NO₃expunged from the trap may go to the catalyst 71. Here, the NO₃may shed N₂and take on CO to form NO in the catalyst.
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—NO₂conversion efficiency at a full exhaust flow rate. The material in section 73 may be some other comparable material. The trapping material Ba₂CO₃in 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 Ba₂NO₃. The NO₃from 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.
FIG. 8 reveals a continuously rotating lean NO trap (LNT) of an assembly 40 having an absorption NO_xelement 109 in a section 101. Section 102 may have an oxidation catalyst (O_xC) 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_xC 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.
FIG. 9 shows a continuously rotating lean NO_xtrap (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_xC) 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_xtrap 50.
FIG. 10 shows a continuously rotating lean NO_xtrap (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.
In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.
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.

Claims

1. A regenerative system comprising:

a catalytic converter having an input and an output;

a first valve connected to the output of the catalytic converter;

a first trap having an input connected to a first output of the first valve; and

a second trap having an input connected to a second output of the first valve;

a second valve having an input connected to an output of the first trap; and

a third valve having an input connected to an output of the second trap.

2. The system of claim 1, further comprising a multiple way catalytic converter having a first input connected to an output of the second valve and connected to an output of the third valve.

3. The system of claim 2, wherein the first and second traps are first and second NO_xtraps, respectively.

4. The system of claim 3, further comprising:

a burner having an output;

a fourth valve having an input connected to the output of the burner, having a first output connected to the input of the first NO_xtrap, and having a second output connected to the input of the second NO_xtrap.

5. The system of claim 4, wherein each of the first, second, third and fourth valves has an actuator.

6. The system of claim 5, further comprising a processor connected to the actuators of the first, second, third and fourth valves.

7. The system of claim 6 wherein:

each of the first, second, third and fourth valves has at least a first position and a second position;

the first position provides for a flow of exhaust gas from the catalytic converter to the first NO_xtrap, and a flow of a regenerative gas to the second NO_xtrap; and

the second position provides for a flow of exhaust gas from the catalytic converter to the second NO_xtrap, and a flow of a regenerative gas to the first NO_xtrap.

8. The system of claim 7, wherein the first and second NO_xtraps are lean NO_xtraps.

9. An instrumentation-equipped exhaust system comprising:

a pre-catalyst device having an output;

a dual trap having an input connected to the output of the pre-catalyst device, and having outputs;

a filter having an input connected to the outputs of the dual trap.

10. The system of claim 9, wherein:

the pre-catalyst device is an oxidation catalyst device;

the dual trap comprises NO_xadsorber catalyst devices; and

the filter is a catalytic particulate filter.

11. The system of claim 9, wherein:

the pre-catalyst is for altering a temperature of an exhaust gas;

the dual trap is for adsorbing NO_x; and

the filter is for trapping particulates from the exhaust gas.

12. The system of claim 11, wherein while one trap of the dual trap is trapping NO_x, another trap of the dual trap is being regenerated.

13. The system of claim 12, further comprising:

a first temperature sensor situated at an input of the pre-catalyst; and

a second temperature sensor situated at the output of the pre-catalyst.

14. The system of claim 13, further comprising a processor connected to the first and second temperature sensors.

15. The system of claim 14, further comprising a third and fourth temperature sensors situated between the outputs of the dual trap and the input of the filter.

16. The system of claim 15, further comprising a fifth temperature sensor situated at an output of the filter.

17. The system of claim 12, further comprising:

a first pressure sensor at the input of the pre-catalyst device; and

a second pressure sensor between the output of the pre-catalyst device and the input of the dual trap.

18. The system of claim 17, further comprising:

third and fourth pressure sensors between the outputs of the dual trap and the input of the filter; and

a fifth pressure sensor at the output of the filter.

19. The system of claim 17, further comprising differential pressure sensors situated at the input and the output of the filter.

20. The system of claim 17, further comprising:

a first NO_xsensor situated at the output of the pre-catalyst device; and

a second and third NO_xsensors situated at the outputs, respectively, of the dual trap.

21. The system of claim 9, further comprising:

a collector;

a first sampling line connected to the collector and between the output of the pre-catalyst device and the input of the dual trap; and

a second sampling line connected to the collector and the input of the filter.

22. The system of claim 21, further comprising a third sampling line connected to the collector and the output of the filter.

23. The system of claim 22, further comprising a fourth sampling line connected to the collector and the input of the pre-catalyst device.

24. An emissions trap assembly comprising:

a rotatable emissions trap having a first end and a second end;

a first section attached to the first end of the rotatable emissions trap; and

a second section attached to the second end of the rotatable emissions trap.

25. The assembly of claim 24, wherein:

a first portion of the first section is a catalyst device;

a second portion of the first section is a burner;

a first portion of the second section is an emissions trap; and

a second portion of the second section is a multiple way catalyst.

26. The assembly of claim 25, wherein:

an exhaust gas may flow through the first portion of the first section, at least a portion of the rotatable emissions trap and the first portion of the second section; and

a regenerative gas may flow from the second portion of the first section, through at least a portion of the rotatable emissions trap and through the second portion of the second section.