US20080202097A1

US20080202097A1 - Engine exhaust treatment system

Info

Publication number: US20080202097A1
Application number: US11/711,657
Authority: US
Inventors: James Joshua Driscoll; Amit Jayachandran
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2007-02-28
Filing date: 2007-02-28
Publication date: 2008-08-28
Also published as: WO2008105996A1

Abstract

An engine exhaust treatment system is provided. The system may include a catalyst-based device including a catalyst configured to reduce an amount of NO_xin exhaust gases produced by an engine, by using ammonia stored in the catalyst-based device. The system may also include a controller configured to control one or more operating parameters of the engine to, under predetermined operating conditions of the engine or catalyst-based device, increase an amount of NO_xproduced by the engine to prevent at least some of the ammonia stored in the catalyst-based device from being released from the catalyst-based device into the exhaust.

Description

TECHNICAL FIELD

The present disclosure is directed to a engine exhaust treatment system and, more particularly, to an engine exhaust treatment system configured to prevent ammonia slip.

BACKGROUND

Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of both solid material, such as, for example, particulate matter, and gaseous material, which may include, for example, oxides of nitrogen, such as NO₂and NO₃(commonly referred to collectively as “NO_x”).
Due to increased environmental concerns, exhaust emission standards have become more stringent. The amount of particulate matter and gaseous pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. In order to meet these emissions standards, engine manufacturers have pursued improvements in several different engine technologies, such as fuel injection, engine management, and air induction, to name a few.
In addition, engine manufacturers have developed devices for treatment of engine exhaust after it leaves the engine (sometimes referred to as “after-treatment”). For example, engine manufacturers have employed exhaust treatment devices that utilize catalysts to convert one or more components of the exhaust to different, more environmentally-friendly compounds. Catalyst-based devices have been developed for reducing or removing NO_xfrom the exhaust stream. In some systems, NO_xmay be reduced by selective catalytic reduction (commonly referred to as “SCR”). In such systems, urea may be added to a catalyst-based device, where it is broken down into ammonia (NH₃) that is stored in (or on) the catalyst. The ammonia stored in the catalyst reacts with NO_xin the exhaust to thereby convert the NO_xto Nitrogen (N₂) and water (H₂O).
The amount of ammonia that can be stored in a catalyst may depend on the temperature of the catalyst. Generally, the hotter the catalyst, the less ammonia that can be stored in it. Therefore, one problem with such systems is that if operating conditions cause an increase in catalyst temperature that happens rapidly, then some of the ammonia in the catalyst may be released into the exhaust and carried downstream from the catalyst-based device and exhausted into the atmosphere with the exhaust gases. This is commonly referred to as “ammonia slip.”
Systems have been developed to prevent ammonia slip. For example, some systems attempt to precisely control the amount of ammonia in the catalyst to correspond to the amount of NO_xproduced by the engine. These systems operate by selectively injecting urea (which breaks down into ammonia) into the catalyst in varying amounts/rates depending on the operating conditions of the engine and/or catalyst. Generally, the injection of urea is controlled, based on the amount of NO_xproduced by the engine, in order to maintain a predetermined maximum amount of ammonia in the catalyst, while taking into account that less ammonia may be stored in the catalyst as catalyst temperatures rise. For example, as catalyst temperatures rise, ammonia injection may be reduced or stopped. However, even with no ammonia injection, the consumption of ammonia already in the catalyst (i.e., via the reaction with NO_x) may be relatively slow compared to the rate at which the capacity of the catalyst to retain ammonia is diminished. Therefore, such systems must predict NO_xoutput by predicting future engine operating parameters, because in order to prevent ammonia slip when catalyst temperature is increasing, the urea injection must be reduced or stopped early to allow time for the amount of ammonia already in the catalyst to be consumed before the decrease in the capacity of the catalyst to retain ammonia leads to excess ammonia being released by the catalyst (i.e., ammonia slip).
One system has been developed that not only controls injection of NO_xreducing agents, but also regulates the amount of NO_xproduced by the engine by controlling engine operating parameters to produce less NO_xunder certain operating conditions. U.S. Pat. No. 5,845,487 issued to Fraenkle et al. (“the '487 patent”) discloses a system configured to reduce both injection of NO_xreducing agents and NO_xoutput by the engine during cold-start warm up. Once operating temperatures exceed a predetermined threshold, the system switches over to a higher engine NO_xoutput operating condition and increased injection of NO_xreducing agents.
While the control strategy employed by the '487 patent may attempt to address certain emissions concerns during cold-start conditions, the control strategy does not address the issue of ammonia slip, particularly during conditions other than cold-start. In addition, the control strategy of the '487 patent modifies the engine operating parameters under some conditions in a manner that reduces fuel efficiency.
The present disclosure is directed at solving one or more of the problems discussed above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to an engine exhaust treatment system. The system may include a catalyst-based device including a catalyst configured to reduce an amount of NO_xin exhaust gases produced by an engine, by using ammonia stored in the catalyst-based device. The system may also include a controller configured to control one or more operating parameters of the engine to, under predetermined operating conditions of the engine or catalyst-based device, increase an amount of NO_xproduced by the engine to prevent at least some of the ammonia stored in the catalyst-based device from being released from the catalyst-based device into the exhaust.
In another aspect, the present disclosure is directed to a method of exhaust treatment. The method may include storing ammonia in a catalyst-based device, wherein the catalyst-based device includes a catalyst configured to reduce an amount of NO_xin exhaust gases produced by the engine by using the ammonia stored in the catalyst-based device. The method may also include controlling, with a controller, one or more operating parameters of the engine to, under predetermined operating conditions of the engine or the catalyst-based device, increase an amount of NO_xproduced by the engine to prevent at least some of the ammonia stored in the catalyst-based device from being released from the catalyst-based device into the exhaust.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a machine according to an exemplary disclosed embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a machine 10. Machine 10 may include a frame 12, an operator station 14, one or more traction devices 16, and a power system 17. Power system 17 may include an exhaust producing engine 18 and an engine exhaust treatment system 20 configured to reduce the amount of one or more constituents of the exhaust produced by engine 18.
Although machine 10 is shown as a truck, machine 10 could be any type of machine having an exhaust producing engine. Accordingly, traction devices 16 may be any type of traction devices, such as, for example, wheels, as shown in FIG. 1, tracks, belts, or any combinations thereof.
Engine 18 may be mounted to frame 12 and may include any kind of engine that produces an exhaust flow of exhaust gases. For example, engine 18 may be an internal combustion engine, such as a gasoline engine, a diesel engine, a natural gas engine or any other exhaust gas producing engine. Engine 18 may be naturally aspirated or, in other embodiments, may utilize forced induction (e.g., turbocharging or supercharging).
System 20 may include, among other things, a controller 22, an exhaust conduit 26, and one or more after-treatment devices 28. These and other components of system 20 will be discussed in greater detail below.
Controller 22 may include any means for receiving machine operating parameter-related information and/or for monitoring, recording, storing, indexing, processing, and/or communicating such information. These means may include components such as, for example, a memory, one or more data storage devices, a central processing unit, or any other components that may be used to run an application.
Although aspects of the present disclosure may be described generally as being stored in memory, one skilled in the art will appreciate that these aspects can be stored on or read from types of computer program products or computer-readable media, such as computer chips and secondary storage devices, including hard disks, floppy disks, optical media, CD-ROM, or other forms of RAM or ROM. Various other known circuits may be associated with controller 22, such as power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry, and other appropriate circuitry.
Controller 22 may be configured to perform multiple processing and controlling functions, such as, for example, engine management (e.g., controller 22 may include an engine control module, a.k.a. an ECM), monitoring/calculating various parameters related to exhaust output and after-treatment thereof, etc. In some embodiments, machine 10 may include multiple controllers (a configuration not shown), each dedicated to perform one or more of these or other functions. Such multiple controllers may be configured to communicate with one another.
After-treatment devices 28 may include a catalyst-based device 30 (e.g., a catalytic converter). Catalyst-based device 30 may include a catalyst 32 configured to convert (e.g., via oxidation or reduction) one or more gaseous constituents of the exhaust stream produced by engine 18 to a more environmentally friendly gas and/or compound to be discharged into the atmosphere. For example, catalyst 32 may be configured to chemically alter at least one component of the exhaust flow. Catalyst-based device 30 may be configured for one or more various types of conversion, such as, for example, select catalytic reduction (SCR), diesel oxidation (e.g., a diesel oxidation catalyst, DOC), and/or adsorption of nitrous oxides (NO_x; e.g., a NO_xadsorber).
After-treatment devices 28 may also include a particulate trap 34. Particulate trap 34 may include any type of after-treatment device configured to remove one or more types of particulate matter, such as soot and/or ash, from an exhaust flow of engine 18. Particulate trap 34 may include a filter medium 36 configured to trap the particulate matter as the exhaust flows through it. Filter medium may consist of a mesh-like material, a porous ceramic material (e.g., cordierite), or any other material and/or configuration suitable for trapping particulate matter.
In some embodiments, after-treatment devices 24 may include combinations of these types of devices. For example, after-treatment devices 28 may include one or more catalytic particulate traps (not shown), which may include a catalytic material integral with filter medium 36. For example, catalyst 32 may be packaged with, coated on, or otherwise associated with filter medium 36. In some embodiments, filter medium 36 may, itself, be a catalytic material. In some embodiments, there may be only a single after-treatment device 28 that is a combined particulate trap/catalyst-based device. In addition, although system 20 is shown with a single catalyst-based device 30 and a single particulate trap 34, system 20 may include more than one of either or both. In other embodiments, system 20 may include more than one catalytic particulate trap. Such multiple after-treatment devices may be positioned in series (e.g., along exhaust conduit 26) or in parallel (e.g., in dual exhaust conduits; not shown). In some embodiments, catalyst-based device 30 may be positioned downstream from particulate trap 34. In other embodiments, catalyst-based device 30 may be positioned upstream from particulate trap 34.
In some embodiments, catalyst-based device 30 may be configured for selective catalytic reduction (SCR). In such embodiment, system 20 may include a urea injector 38 configured to inject urea into exhaust conduit 26 and/or directly into catalyst-based device 30. The injected urea may be broken down into ammonia, which may be retained within catalyst-based device 30. The ammonia stored in catalyst-based device 30 may reduce the amount of NO_xin the exhaust gases passing through catalyst-based device 30. Alternatively or additionally, other agents suitable for reducing NO_xmay be injected into exhaust conduit 26 and/or catalyst-based device 30.
In embodiments configured for SCR, catalyst 32 may be configured to reduce the amount of NO_xin the exhaust gases produced by engine 18 by using ammonia stored in catalyst-based device 30. Controller 22 may be configured to control one or more operating parameters of engine 18 to, under predetermined operating conditions of engine 18 or catalyst-based device 30, increase an amount of NO_xproduced by engine 18 to prevent at least some of the ammonia stored in catalyst-based device 30 from being released from catalyst-based device 30 into the exhaust.
System 20 may include a temperature sensor 40 configured to detect a temperature associated with catalyst-based device 30. In one embodiment, temperature sensor 40 may be configured to detect inlet temperature of catalyst-based device 30, as illustrated in FIG. 1. Alternatively, temperature sensor 40 may be positioned at any location suitable to detect a temperature associated with catalyst-based device 30. For example, temperature sensor 40 may be located along exhaust conduit 26 somewhat upstream from catalyst-based device 30, such that the temperature of catalyst-based device 30 may be predicted based on the upstream exhaust gas temperature detected by temperature sensor 40. In other embodiments, temperature sensor 40 may be what may be referred to as a “virtual sensor.” For example, a virtual temperature sensor may be derived by controller 22 by monitoring one or more engine and/or exhaust operating parameters and predicting the inlet temperature of catalyst-based device 30 based on the monitored operating parameters.
In some embodiments, controller 22 may be configured to monitor the rate of temperature increase measured by temperature sensor 40. Controller 22 may be configured to increase the amount of NO_xproduced by engine 18 when the rate of increase of a temperature associated with the catalyst-based device is faster than a predetermined rate of temperature increase. Rapid rates of catalyst temperature increase may occur when exhaust temperatures rise quickly, such as upon increased engine load. Increases in engine load may occur, for example, due to acceleration of engine 18 and/or acceleration of machine 10 or due to machine 10 suddenly starting to drive uphill, thus increasing the load-on engine 18.
In one embodiment, when the inlet temperature of catalyst-based device 30, as measured by temperature sensor 40, is increasing faster than a predetermined rate of increase, the capacity of catalyst-based device 30 to retain ammonia may be decreasing at a rate fast enough to cause ammonia to be released (i.e., ammonia slip) before it may be used to react with NO_xin the exhaust flowing through catalyst-based device 30. In order to prevent the ammonia from being released from catalyst-based device 30 due to the decrease in capacity, controller 22 may increase the amount of NO_xproduced by engine 18, when the catalyst inlet temperature is increasing faster than a predetermined rate of increase. The extra NO_xin the exhaust gases may react with more ammonia, causing the ammonia to be “consumed” in the NO_xreduction reaction before the ammonia slip occurs.
System 20 may effectuate the increased NO_xoutput of engine 18 in any number of different ways. Controller 22 may be configured to increase NO_xoutput of engine 18 by changing one or more operating parameters of engine 18. For example, controller 22 may be configured to increase the amount of NO_xproduced by engine 18 by advancing injection timing, reducing exhaust gas recirculation flowrate, increasing injection pressure, and/or changing valve actuation strategy. In addition to reducing or preventing ammonia slip, these changes in engine operating parameters may also improve fuel efficiency of engine 18. Alternatively or additionally, other changes to operating parameters of engine 18 that cause an increase in NO_xproduction may be employed.
In addition to increasing NO_xoutput of engine 18 under the predetermined operating conditions (e.g., rapid increases in catalyst temperature), the controller may also be configured to reduce the amount of urea injected into catalyst-based device 30, under such conditions. In some embodiments, reducing the urea injection may include completely ceasing urea injection under predetermined operating conditions.

INDUSTRIAL APPLICABILITY

The disclosed system may be suitable to enhance exhaust emissions control for engines. The disclosed system may be used for any application of an engine. Such applications may include supplying power for machines, such as, for example, stationary equipment such as power generation sets, or mobile equipment, such as vehicles. The disclosed system may be used for any kind of vehicle, such as, for example, automobiles, construction machines (including those for on-road, as well as off-road use), and other heavy equipment.
Not only may the disclosed system be applicable to various applications of an engine, but the disclosed system may be applicable to various types of engines as well. For example, the disclosed system may be applicable to any exhaust producing engine, which may include gasoline engines, diesel engines, natural gas engines, hydrogen engines, etc. The disclosed system may also be applicable to a variety of engine configurations, including various cylinder configurations, such as “V” cylinder configurations (e.g., V6, V8, V12, etc.), inline cylinder configurations, and horizontally opposed cylinder configurations. The disclosed system may also be applicable to engines with a variety of induction types. For example, the disclosed system may be applicable to normally aspirated engines, as well as those with forced induction (e.g., turbocharging or supercharging). Engines to which the disclosed system may be applicable may include combinations of these configurations (e.g., a turbocharged, inline-6 cylinder, diesel engine).
The disclosed system may also be applicable to various exhaust path configurations. For example, the disclosed system may be applicable to exhaust systems that employ a single exhaust conduit (e.g., the exhaust from each cylinder ultimately feeds into a single conduit, such as after an exhaust manifold). The disclosed system may also be applicable to dual exhaust systems (e.g., different groups of cylinders may feed into separate exhaust conduits). In such systems, many of the components of the disclosed system may be provided in duplicate (e.g., one catalyst-based device for each exhaust conduit, one particulate trap for each conduit, etc.).
Further, where appropriate, the disclosed system may provide more than one of certain components that have been shown and discussed herein as singular components. For example, in any given embodiment, the disclosed system may include more than one catalyst-based device, regardless of the exhaust configuration utilized in that embodiment.
An exemplary method of exhaust treatment using the disclosed system may include storing ammonia in a catalyst-based device, wherein the catalyst-based device includes a catalyst configured to reduce an amount of NO_xin exhaust gases produced by the engine by using the ammonia stored in the catalyst-based device. The exemplary method may also include controlling, with a controller, one or more operating parameters of the engine to, under predetermined operating conditions of the engine or the catalyst-based device, increase the amount of NO_xproduced by the engine to prevent at least some of the ammonia stored in the catalyst-based device from being released from the catalyst-based device into the exhaust. In some embodiments, the method may include reducing an amount of urea injected into the catalyst-based device, under the predetermined operating conditions. In some embodiments, increasing the amount of NO_xproduced by the engine may be accomplished at least in part by advancing injection timing, reducing exhaust gas recirculation flowrate, increasing injection pressure, and/or changing valve-actuation strategy.
In addition to preventing ammonia slip, the disclosed system may provide other advantages, such as improving fuel economy. As discussed above, operating an engine in a manner that produces more NO_xmay be more fuel efficient. Further, the disclosed system may also make it possible to use smaller catalyst-based devices because, with the disclosed system, more ammonia may be stored in the catalyst at any given time without risking ammonia slip upon subjecting the catalyst to rapid temperature increases.
It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the disclosed exhaust treatment system without departing from the scope of the invention. Other embodiments of the invention will be apparent to those having ordinary skill in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.

Claims

1. An engine exhaust treatment system, comprising:

a catalyst-based device including a catalyst configured to reduce an amount of NOx in exhaust gases produced by an engine, by using reductant stored in the catalyst-based device; and

a controller configured to control one or more operating parameters of the engine to, in response to a rate of increase of a temperature associated with the catalyst-based device, increase an amount of NOx produced by the engine to prevent at least some of the reductant stored in the catalyst-based device from being released from the catalyst-based device into the exhaust.

2. The exhaust treatment system of claim 1, wherein the controller is configured to control one or more operating parameters of the engine in response to the rate of increase of the temperature associated with the catalyst-based device being faster than a threshold rate of temperature increase.

3. The exhaust treatment system of claim 2, wherein, in response to the rate of increase of the temperature associated with the catalyst-based device being faster than a threshold rate of temperature increase, the controller is further configured to reduce an amount of urea injected into the catalyst-based device.

4. The exhaust treatment system of claim 1, wherein the controller is configured to increase the amount of NOx produced by the engine by advancing injection timing.

5. The exhaust treatment system of claim 1, wherein the controller is configured to increase the amount of NOx produced by the engine by reducing exhaust gas recirculation flowrate.

6. The exhaust treatment system of claim 1, wherein the controller is configured to increase the amount of NOx produced by the engine by increasing injection pressure.

7. The exhaust treatment system of claim 1, wherein the controller is configured to increase the amount of NOx produced by the engine by changing valve actuation strategy.

8. A method of exhaust treatment, comprising:

storing reductant in a catalyst-based device, wherein the catalyst-based device includes a catalyst configured to reduce an amount of NOx in exhaust gases produced by an engine by using the reductant stored in the catalyst-based device; and

controlling one or more operating parameters of the engine to, in response to a rate of increase of a temperature associated with the catalyst-based device, increase an amount of NOx produced by the engine to prevent at least some of the reductant stored in the catalyst-based device from being released from the catalyst-based device into the exhaust.

9. The method of claim 8, wherein controlling one or more operating parameters of the engine occurs in response to the rate of increase of the temperature associated with the catalyst-based device being faster than a threshold rate of temperature increase.

10. The method of claim 8, further including reducing an amount of urea injected into the catalyst-based device, in response to the rate of increase of the temperature associated with the catalyst-based device being faster than a threshold rate of temperature increase.

11. The method of claim 8, wherein increasing the amount of NOx produced by the engine is accomplished at least in part by advancing injection timing.

12. The method of claim 8, wherein the increasing the amount of NOx produced by the engine is accomplished at least in part by reducing exhaust gas recirculation flowrate.

13. The method of claim 8, wherein the increasing the amount of NOx produced by the engine is accomplished at least in part by increasing injection pressure.

14. The method of claim 8, wherein the increasing the amount of NOx produced by the engine is accomplished at least in part by changing valve actuation strategy.

15. A power system, comprising:

an exhaust producing engine; and

an engine exhaust treatment system configured to reduce an amount of one or more constituents of the exhaust produced by the engine, the engine exhaust treatment system including:

a catalyst-based device including a catalyst configured to reduce an amount of NOx in exhaust gases produced by the engine, by using reductant stored in the catalyst-based device; and

a controller configured to control one or more operating parameters of the engine to, in response to a rate of increase of a temperature associated with the catalyst-based device being faster than a threshold rate of temperature increase, increase an amount of NOx produced by the engine to prevent at least some of the reductant stored in the catalyst-based device from being released from the catalyst-based device into the exhaust;

16. The power system of claim 15, wherein, in response to the rate of increase of the temperature associated with the catalyst-based device being faster than the threshold rate of temperature increase, the controller is further configured to reduce an amount of urea injected into the catalyst-based device.

17. The power system of claim 15, wherein the controller is configured to increase the amount of NOx produced by the engine by advancing injection timing.

18. The power system of claim 15, wherein the controller is configured to increase the amount of NOx produced by the engine by reducing exhaust gas recirculation flowrate.

19. The power system of claim 15, wherein the controller is configured to increase the amount of NOx produced by the engine by increasing injection pressure.

20. The power system of claim 15, wherein the controller is configured to increase the amount of NOx produced by the engine by changing valve actuation strategy.