WO2008042048A1

WO2008042048A1 - Managing temperature in an exhaust treatment system

Info

Publication number: WO2008042048A1
Application number: PCT/US2007/017761
Authority: WO
Inventors: Christopher R. Gehrke; Justin W. Mcmenamy
Original assignee: Caterpillar Inc.
Priority date: 2006-09-29
Filing date: 2007-08-10
Publication date: 2008-04-10
Also published as: US20080078170A1; DE112007002202T5; CN101535607A

Abstract

A method of controlling an exhaust treatment system (10, 100) includes sensing a temperature representative of a catalyst material temperature at start-up of a power source (12) and comparing the sensed temperature to a threshold temperature. The method also includes igniting a regeneration device (20) of the exhaust treatment system (10, 100) in response to the comparing. The regeneration device (20) is disposed upstream of the catalyst material. The method further includes operating the regeneration device (20) at a target temperature.

Description

MANAGING TEMPERATURE IN AN EXHAUST TREATMENT SYSTEM

Technical Field

The present disclosure relates generally to an exhaust treatment system and, more particularly, to managing the temperature of one or more components of an exhaust treatment system with a regeneration device.

Background

Internal combustion 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 pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx), and solid particulate matter. Particulate matter may include soluble organic fraction, soot (unburned carbon), and/or unburned hydrocarbons.

Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of pollutants emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions is exhaust gas recirculation (EGR). EGR systems recirculate the exhaust gas byproducts into the intake air supply of the internal combustion engine. The exhaust gas directed to the engine cylinder reduces the concentration of oxygen within the cylinder and increases the specific heat of the air/fuel mixture, thereby lowering the maximum combustion temperature within the cylinder. The lowered maximum combustion temperature and reduced oxygen concentration can slow the chemical reaction of the combustion process and decrease the formation of NOx. In many EGR applications, the exhaust gas is passed through a particulate filter configured to capture and/or otherwise extract a portion of the soot, soluble organic fraction, and/or unbumed hydrocarbons contained carried by the exhaust. After a period of use, the particulate filter may become saturated and may require cleaning through a regeneration process wherein the particulate matter is purged from the filter. In addition, the particulate filter may include one or more catalyst materials configured to oxidize a portion of the soot, soluble organic fraction, and/or unburned hydrocarbons contained within the exhaust gas. The catalyst materials may also assist in reducing NOx and/or carbon monoxide present in the exhaust.

The catalyst materials may be most effective at temperatures in excess of their passive regeneration or "light-off temperature (the temperature at which the catalyst materials are capable of spontaneously oxidizing particulate matter). Thus, the catalyst materials are said to have a relatively high conversion efficiency above their light-off temperatures, and peak conversion efficiency of the materials may occur in the range of approximately 300 degrees Celsius to approximately 450 degrees Celsius. At relatively low temperatures, however, such as, for example, during engine start-up or during a prolonged idling period, the catalyst materials may not be capable of oxidizing the particulate matter. As a result, the amount of pollutants emitted by the system may exceed the maximum emissions limits set forth by the Environmental Protection Agency when the catalyst materials are at relatively low temperatures. Such operating conditions may be characterized by an increase in the amount of whitesmoke exiting the system as well as an increase in the intensity and amount of unpleasant odors given off.

As shown in U.S. Patent No. 6,427,436 ("the '436 patent"), a filter system can be used to remove particulate matter from a flow of engine exhaust gas before a portion of the gas is fed back to an intake air stream of the engine. Specifically, the '436 patent discloses an engine exhaust filter containing a catalyst and a filter element. A portion of the filtered exhaust is extracted downstream of the filter and is directed to an intake of the engine through a recirculation loop.

Although the filter system of the '436 patent may protect the engine from harmful particulate matter, the system may not be configured to improve the effectiveness of catalyst materials located in the system by actively increasing the temperature of the catalyst materials to a predetermined temperature within their peak conversion efficiency range.

The disclosed exhaust treatment system is directed to overcoming one or more of the problems set forth above.

Summary of the Invention

In one embodiment of the present disclosure, a method of controlling an exhaust treatment system includes sensing a temperature representative of a catalyst material temperature at start-up of a power source and comparing the sensed temperature to a threshold temperature. The method also includes igniting a regeneration device of the exhaust treatment system in response to the comparing. The regeneration device is disposed upstream of the catalyst material. The method further includes operating the regeneration device at a target temperature. In another embodiment of the present disclosure, a method of reducing the emissions of an internal combustion engine includes igniting a regeneration device fluidly connected to the internal combustion engine and increasing the temperature of a catalyst material to a target temperature during a low exhaust temperature operation of the internal combustion engine. The method also includes maintaining the temperature of the catalyst material at the target temperature for a predetermined period of time.

In yet another embodiment of the present disclosure, an exhaust treatment system of a power source includes a catalyst material and a regeneration device disposed upstream of the catalyst material. The regeneration device is configured to increase a temperature of the catalyst material to a target temperature at start-up of the power source and in response to a sensed parameter of the exhaust treatment system. The system further includes a particulate filter configured to extract components from an exhaust flow of the power source.

Brief Description of the Drawings

Fig. 1 is a diagrammatic illustration of an engine having an exhaust treatment system according to an exemplary embodiment of the present disclosure.

Fig. 2 is a diagrammatic illustration of an engine having an exhaust treatment system according to another exemplary embodiment of the present disclosure.

Fig. 3 is a flow chart of a control strategy according to an exemplary embodiment of the present disclosure.

Detailed Description Fig. 1 illustrates a power source 12 having an exemplary exhaust treatment system 10. The power source 12 may include an engine, such as, for example, a diesel engine, a gasoline engine, a natural gas engine, or any other engine apparent to one skilled in the art. The power source 12 may, alternately, include another source of power, such as a furnace or any other source of power known in the art.

The exhaust treatment system 10 may be configured to direct exhaust gases out of the power source 12, treat the gases, and introduce a portion of the treated gases into an inlet 21 of the power source 12. The exhaust treatment system 10 may include an energy extraction assembly 22 and a treatment element 19. The treatment element 19 may include, for example, a regeneration device 20, a filter 16, and/or a catalyst 18. The exhaust treatment system 10 may further include a recirculation line 24 fluidly connected between the filter 16 and the catalyst 18, and a flow cooler 26. The exhaust treatment system 10 may still further include a flow sensor 28, a mixing valve 30, a compression assembly 32, and an aftercooler 34.

A flow of exhaust produced by the power source 12 may be directed from the power source 12 to components of the exhaust treatment system 10 by flow lines 15. It is understood that the power source 12 may include one or more combustion chambers (not shown) fluidly connected to an exhaust manifold. In such an exemplary embodiment, the flow lines 15 may be configured to transmit a flow of exhaust from the combustion chambers to the components of the exhaust treatment system 10 via the exhaust manifold. The flow lines 15 may include pipes, tubing, and/or other exhaust flow carrying means known in the art. The flow lines 15 may be made of alloys of steel, aluminum, and/or other materials known in the art. The flow lines 15 may be rigid or flexible, and may be capable of safely carrying high temperature exhaust flows, such as flows having temperatures in excess of 700 degrees Celsius (approximately 1,292 degrees Fahrenheit).

The energy extraction assembly 22 may be configured to extract energy from, and reduce the pressure of, the exhaust gases produced by the power source 12. The energy extraction assembly 22 may be fluidly connected to the power source 12 by one or more flow lines 15 and may reduce the pressure of the exhaust gases to any desired pressure. The energy extraction assembly 22 may include one or more turbines 14, diffusers, or other energy extraction devices known in the art. In an exemplary embodiment wherein the energy extraction assembly 22 includes more than one turbine 14, the multiple turbines 14 may be disposed in parallel or in series relationship. It is also understood that in an embodiment of the present disclosure, the energy extraction assembly 22 may, alternately, be omitted. In such an embodiment, the power source 12 may include, for example, a naturally aspirated engine. As will be described in greater detail below, a component of the energy extraction assembly 22 may be configured in certain embodiments to drive a component of the compression assembly 32.

In an exemplary embodiment, the regeneration device 20 of the treatment element 19 may be fluidly connected to the energy extraction assembly 22 via flow line 15 and may be configured to increase the temperature of an entire flow of exhaust produced by the power source 12 to a desired temperature. The desired temperature may be, for example, a regeneration temperature of the filter 16. Accordingly, the regeneration device 20 may be configured to assist in actively regenerating the filter 16. Alternatively, the desired temperature may be, for example, a threshold temperature corresponding to the minimum passive regeneration or light-off temperature of catalyst materials disposed downstream of the regeneration device 20. The desired temperature may also be a target temperature corresponding to, for example, a peak conversion efficiency range of the catalyst materials. This peak conversion efficiency range of the materials may occur in the range of approximately 300 degrees Celsius to approximately 450 degrees Celsius, and in an exemplary embodiment, the target temperature may be between approximately 300 degrees Celsius and approximately 350 degrees Celsius. The target temperature may also correspond to a minimum temperature setting of the regeneration device 20. As will be discussed below, such catalyst materials may be disposed within a catalyst 18 of the exhaust treatment system 10. Alternatively, such catalyst materials may be disposed within a filter 36 (FIG. 2) of the present disclosure. In another exemplary embodiment, the regeneration device 20 may be configured to increase the temperature of only a portion of the entire flow of exhaust produced by the power source 12.

The regeneration device 20 may include, for example, a fuel injector and an ignitor (not shown), heat coils (not shown), and/or other heat sources known in the art. Such heat sources may be disposed within the regeneration device 20 and may be configured to assist in increasing the temperature of the flow of exhaust through convection, combustion, and/or other methods. In an exemplary embodiment in which the regeneration device 20 includes a fuel injector and an ignitor, it is understood that the regeneration device 20 may receive a supply of a combustible substance and a supply of oxygen to facilitate combustion within the regeneration device 20. The combustible substance may be, for example, gasoline, diesel fuel, reformate, and/or any other combustible substance known in the art. The supply of oxygen may be provided in addition to the relatively low pressure flow of exhaust gas directed to the regeneration device 20 through flow line 15. In an exemplary embodiment, the supply of oxygen may be carried by a flow of gas directed to the regeneration device 20 from downstream of the compression assembly 32 via a supply line 40. In such an embodiment, the flow of gas may include, for example, recirculated exhaust gas and ambient air. It is understood that, in an exemplary embodiment of the present disclosure, the supply line 40 may be fluidly connected to an outlet of the compression assembly 32. In an exemplary embodiment, the regeneration device 20 may be dimensioned and/or otherwise configured to be housed within an engine compartment or other compartment of a work machine (not shown) to which the power source 12 is attached. In such an embodiment, the regeneration device 20 may be desirably calibrated in conjunction with, for example, the filter 16, the energy extraction assembly 22, the catalyst 18, and/or the power source 12. Calibration of the regeneration device 20 may include, for example, among other things, adjusting the rate, angle, and/or atomization at which fuel is injected into the regeneration device 20, adjusting the flow rate of the oxygen supplied, adjusting the intensity and/or firing pattern of the ignitor, and adjusting the length, diameter, mounting angle, and/or other configurations of a housing of the regeneration device 20. Such calibration may reduce the time required to regenerate the filter 16 and the amount of fuel or other combustible substances needed for regeneration. Either of these results may improve the overall efficiency of the exhaust treatment system 10. It is understood that the efficiency of the exhaust treatment systems 10, 100 described herein may be measured by a variety of factors, including, among other things, the amount of fuel used for regeneration, the length of the regeneration period, and the amount (parts per million) of pollutants released to the atmosphere.

As shown in FIG. 1, the filter 16 of the treatment element 19 may be connected downstream of the regeneration device 20. The filter 16 may have a housing 25 including an inlet 23 and an outlet 31. In an exemplary embodiment, the regeneration device 20 may be disposed outside of the housing 25 and may be fluidly connected to the inlet 23 of the housing 25. In another exemplary embodiment, the regeneration device 20 may be disposed within the housing 25 of the filter 16. The filter 16 may be any type of filter known in the art capable of extracting matter from a flow of gas. In an embodiment of the present disclosure, the filter 16 may be, for example, a particulate matter filter positioned to extract particulate matter from an exhaust flow of the power source 12. The filter 16 may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art. These materials may form, for example, a honeycomb structure within the housing 25 of the filter 16 to facilitate the removal of particulate matter. As discussed above, the particulate matter may include, for example, soluble organic fraction, unburned hydrocarbons, and/or soot.

In an exemplary embodiment of the present disclosure, a portion of the exhaust produced by the combustion process may leak past piston seal rings within a crankcase (not shown) of the power source 12. This portion of the exhaust, often called "blow-by gases" or simply "blow-by," may contain one or more of the exhaust gas components discussed above. In addition, because the crankcase is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor. The blow-by gases may build up within the crankcase over time, thereby increasing the pressure within the crankcase. In such an embodiment, a ventilation line 42 may be fluidly connected to the crankcase of the power source 12. The ventilation line 42 may also be fluidly connected to, for example, a port 46 disposed upstream of the filter 16 and/or the regeneration device 20. The ventilation line 42 may comprise piping, tubing, and/or other exhaust flow carrying means known in the art and may be structurally similar to the flow lines 15 described above. The ventilation line 42 may include, for example, a check valve 44 and/or any other valve assembly known in the art. The check valve 44 may be configured to assist in controllably regulating a flow of fluid through the ventilation line 42. In an exemplary embodiment, the check valve 44 may be configured to assist in releasing built-up blow-by gases from the crankcase.

The catalyst 18 of the exhaust treatment system 10 may be disposed downstream of the filter 16. The catalyst 18 may contain catalyst materials useful in collecting, absorbing, adsorbing, and/or storing hydrocarbons, oxides of sulfur, and/or oxides of nitrogen contained in a flow. Such catalyst materials may include, for example, aluminum, platinum, palladium, rhodium, barium, cerium, and/or alkali metals, alkaline-earth metals, rare-earth metals, or combinations thereof. The catalyst materials may be situated within the catalyst 18 so as to maximize the surface area available for the collection of, for example, hydrocarbons. The catalyst 18 may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art, and the catalyst materials may be located on, for example, a substrate of the catalyst 18.

As illustrated in FIG. 2, in an additional exemplary embodiment of the present disclosure, the filter 36 of the exhaust treatment system 100 may include catalyst materials useful in collecting, absorbing, adsorbing, and/or storing hydrocarbons, oxides of sulfur, and/or oxides of nitrogen contained in a flow. In such an embodiment, the catalyst 18 (FIG. 1) may be omitted. The catalyst materials may include, for example, any of the catalyst materials discussed above with respect to the catalyst 18 (FIG. 1). The catalyst materials may be situated within the filter 36 so as to maximize the surface area available for absorption, adsorption, and or storage. The catalyst materials may be located on a substrate of the filter 36. The catalyst materials may be added to the filter 36 by any conventional means, such as, for example, coating or spraying, and the substrate of the filter 36 may be partially or completely coated with the materials. It is understood that the presence of catalyst materials, such as, for example, platinum and/or palladium, upstream of the recirculation line 24 may result in the formation of sulfate in the exhaust treatment system 100. Accordingly, to minimize the amount of sulfate formed in the exemplary embodiment of FIG. 2, only minimal amounts of catalyst materials may be incorporated into the filter 36.

It is also understood that the catalyst materials described above with respect to FIGS. 1 and 2 may be capable of oxidizing one or more components of an exhaust flow, such as, for example, particulate matter, hydrocarbons, and/or carbon monoxide. Thus, in the embodiment shown in FIG. 1, a portion of the particulate matter, hydrocarbons, and/or carbon monoxide contained within the exhaust flow may be permitted to travel back to the power source 12 without being oxidized by the catalyst materials. Although the catalyst materials discussed above may assist in the formation of sulfate, the presence of these catalyst materials, either on a substrate of the filter 36 (FIG. 2) or in the catalyst 18 (FIG. 1), may improve the overall emissions characteristics of the exhaust treatment systems 10, 100 by, for example, removing hydrocarbons from the treated exhaust flow.

It is further understood that in the embodiment shown in FIG. 2, the catalyst materials disposed on the substrate of the filter 36 may assist in passively regenerating the filter 36 during power source operation. As the power source 12 operates, particulates and other components of the power source exhaust may be trapped by the filter substrate. The exhaust flow may reach temperatures in excess of, for example, 250 degrees Celsius during normal operation of the power source 12 (i.e., without operating the power source 12 in a manner so as to increase the temperature of the exhaust by, for example, wastegating or other conventional methods), and the exhaust gas may increase the temperature of at least a portion of the filter substrate through convective heat transfer. At such temperatures, the components of the power source exhaust trapped by the substrate of the filter 36 may begin to react with the catalyst material located on the substrate. In particular, the catalyst material may passively regenerate a portion of the filter 36 by oxidizing particulate matter trapped by the filter substrate as well as carbon monoxide and/or hydrocarbons contained in the exhaust flow. Oxidation may occur at the passive regeneration or light-off temperature of the filter 36 in which the catalyst material is hot enough to react with the components of the exhaust flow without additional heat being provided by, for example, the regeneration device 20. Such light-off temperatures may be below the regeneration temperature of the filter 36. In an exemplary embodiment, a light-off temperature of the filter 36 may be between approximately 250 degrees Celsius and approximately 350 degrees Celsius.

Although at least a portion of the particulate matter contained within the filter 36 may be oxidized and/or removed therefrom through passive regeneration, it is understood that, as shown in FIG. 2, an exemplary exhaust treatment system 100 of the present disclosure may, nonetheless, include a regeneration device 20. Utilizing a catalyzed filter 36 in conjunction with a regeneration device 20 may assist in increasing the interval between active regenerations. Increasing this interval may reduce the amount of, for example, fuel burned during operation of the power source 12 and may, thus, reduce the cost of operating the machine to which the power source 12 is connected. An exhaust treatment system 100 including both a catalyzed filter 36 and a regeneration device 20 may also enable filter manufacturers to include less catalyst material (such as, for example, precious metals) in the filter 36, thereby reducing the cost of the filter 36 and the overall cost of the system 100. Referring again to FIG. 1 , the exhaust treatment system 10 may further include a recirculation line 24 fluidly connected downstream of the filter 16. The recirculation line 24 may be disposed between the filter 16 and the catalyst 18, and may be configured to assist in directing a portion of the exhaust flow from the filter 16 to the inlet 21 of the power source 12. The recirculation line 24 may comprise piping, tubing, and/or other exhaust flow carrying means known in the art, and may be structurally similar to the flow lines 15 described above. In an embodiment in which the exhaust treatment system 100 (FIG. 2) includes a filter 36 containing catalyst materials, the recirculation line 24 may be disposed downstream of the filter 36 and upstream of an exhaust system outlet 17.

The flow cooler 26 may be fluidly connected to the filter 16 via the recirculation line 24 and may be configured to cool the portion of the exhaust flow passing through the recirculation line 24. The flow cooler 26 may include a liquid-to-air heat exchanger, an air-to-air heat exchanger, or any other type of heat exchanger known in the art for cooling an exhaust flow. In an alternative exemplary embodiment of the present disclosure, the flow cooler 26 may be omitted.

The mixing valve 30 may be fluidly connected to the flow cooler 26 via the recirculation line 24 and may be configured to assist in regulating the flow of exhaust through the recirculation line 24. It is understood that in an exemplary embodiment, a check valve (not shown) may be fluidly connected upstream of the flow cooler 26 to further assist in regulating the flow of exhaust through the recirculation line 24. The mixing valve 30 may be a spool valve, a shutter valve, a butterfly valve, a check valve, a diaphragm valve, a gate valve, a shuttle valve, a ball valve, a globe valve, or any other valve known in the art. The mixing valve 30 may be actuated manually, electrically, hydraulically, pneumatically, or in any other manner known in the art. The mixing valve 30 may be in communication with a controller (not shown) and may be selectively actuated in response to one or more predetermined conditions.

The mixing valve 30 may also be fluidly connected to an ambient air intake 29 of the exhaust treatment system 10. Thus, the mixing valve 30 may be configured to control the amount of exhaust flow entering a flow line 27 relative to the amount of ambient air flow entering the flow line 27. For example, as the amount of exhaust flow passing through the mixing valve 30 is desirably increased, the amount of ambient air flow passing through the mixing valve 30 may be proportionally decreased and vice versa. As shown in FIG. 1, the flow sensor 28 may be fluidly connected to the recirculation line 24 downstream of the flow cooler 26. The flow sensor 28 may be any type of mass air flow sensor, such as, for example, a hot wire anemometer or a venturi-type sensor. The flow sensor 28 may be configured to sense the amount of exhaust flow passing through the recirculation line 24. It is understood that the flow cooler 26 may assist in reducing fluctuations in the temperature of the portion of the exhaust flow passing through the recirculation line 24. Reducing temperature fluctuations may also assist in reducing fluctuations in the volume occupied by a flow of exhaust gas since a high temperature mass of gas occupies a greater volume than the same mass of gas at a low temperature. Thus, sensing the amount of exhaust flow through the recirculation line 24 at positions downstream of the flow cooler 26 (i.e., at a relatively controlled temperature) may result in more accurate flow measurements than measurements taken upstream of the flow cooler 26. It is further understood that the flow sensor 28 may also include, for example, a thermocouple (not shown) or other device configured to sense the temperature of the exhaust flow.

The flow line 27 downstream of the mixing valve 30 may direct the ambient air/exhaust flow mixture to the compression assembly 32. The compression assembly 32 may include a compressor 13 configured to increase the pressure of a flow of gas at a desired pressure. The compressor 13 may include a fixed geometry-type compressor, a variable geometry-type compressor, or any other type of compressor known in the art. In the exemplary embodiment shown in FIG. 1, the compression assembly 32 may include more than one compressor 13, and the multiple compressors 13 may be disposed in parallel or in series relationship. A compressor 13 of the compression assembly 32 may be connected to a turbine 14 of the energy extraction assembly 22, and the turbine 14 may be configured to drive the compressor 13. In particular, as hot exhaust gases exit the power source 12 and expand against the blades (not shown) of the turbine 14, components of the turbine 14 may rotate and drive the connected compressor 13. Alternatively, in an embodiment in which the turbine 14 is omitted, the compressor 13 may be driven by, for example, the power source 12, or by any other drive known in the art. It is also understood that in a nonpressurized air induction system, the compression assembly 32 may be omitted.

The aftercooler 34 may be fluidly connected to the power source 12 via the flow line 27 and may be configured to cool a flow of gas passing through the flow line 27. In an exemplary embodiment, this flow of gas may be the ambient air/exhaust flow mixture discussed above. The aftercooler 34 may include a liquid-to-air heat exchanger, an air-to-air heat exchanger, or any other type of flow cooler or heat exchanger known in the art. In an exemplary embodiment of the present disclosure, the aftercooler 34 may be omitted, if desired.

The exhaust treatment system 10 may further include a condensate drain 38 fluidly connected to the aftercooler 34. The condensate drain 38 may be configured to collect a fluid, such as, for example, water or other condensate formed at the aftercooler 34. It is understood that such fluids may consist of, for example, condensed water vapor contained in recycled exhaust gas and/or ambient air. In such an exemplary embodiment, the condensate drain 38 may include a removably attachable fluid tank (not shown) capable of safely storing the condensed fluid. The fluid tank may be configured to be removed, safely emptied, and reconnected to the condensate drain 38. In another exemplary embodiment, the condensate drain 38 may be configured to direct the condensed fluid to a fluid container (not shown) and/or other component or location on the work machine. Alternatively, the condensate drain 38 may be configured to direct the fluid to the atmosphere or to the surface by which the work machine is supported.

Industrial Applicability The exhaust treatment systems 10, 100 of the present disclosure may be used with any combustion-type device, such as, for example, an engine, a furnace, or any other device known in the art where the recirculation of reduced- particulate exhaust into an inlet of the device is desired. The exhaust treatment systems 10, 100 may be useful in reducing the amount of harmful exhaust emissions discharged to the environment. The exhaust treatment systems 10, 100 may also be capable of purging the portions of the exhaust gas captured by components of the system through a regeneration process.

As discussed above, the combustion process may produce a complex mixture of air pollutants. These pollutants may exist in solid, liquid, and/or gaseous form. In general, the solid and liquid pollutants may fall into the three categories of soot, soluble organic fraction, and unburned hydrocarbons. The soot produced during combustion may include carbonaceous materials, and the soluble organic fraction may include unburned hydrocarbons that are deposited on or otherwise chemically combined with the soot. Due to increasing concerns about the health of the environment, the Environmental Protection Agency has mandated that, for 2007, hydrocarbon emissions for on-highway vehicles must be less than or equal to 0.14 grams/horsepower hour. Various exhaust treatment strategies are required in order to meet these stringent emissions requirements at substantially all power source operating conditions. For example, as will be discussed below, components of the exhaust treatment systems 10, 100 such as, for example, the catalyst materials, may be heated when the vehicle is operated at low exhaust temperature conditions. Such conditions may exist, for example, upon start-up of the power source 12 and during a prolonged period of time in which the power source 12 operates at or near idle. In such conditions, the catalyst materials may be below their light-off temperature, and heating the catalyst materials may assist in increasing their conversion efficiency. The operation of the exhaust treatment systems 10, 100 will now be explained in detail. Unless otherwise noted, the exhaust treatment system 100 of FIG. 2 and the control strategy 50 illustrated in FIG. 3 will be referred to for the duration of the disclosure.

At start-up (step 52), sensors of the exhaust treatment system 100 may sense parameters of the power source 12 and/or the exhaust treatment system 100. Such parameters may include, for example, engine speed, engine temperature, exhaust flow temperature, exhaust flow pressure, and/or particulate matter content. The sensors may also be electrically connected to a controller (not shown) and may be configured to send signals containing sensed information to the controller. For example, a temperature sensor 48 may be disposed proximate the outlet 31 of the filter 36 and may be configured to sense the temperature of the exhaust flow exiting the filter 36. Alternatively, the temperature sensor 48 may be disposed proximate an outlet of the catalyst 18 (FIG. 1). Accordingly, the temperature sensor 48 may be configured to sense a temperature representative of catalyst material temperature (step 54) and may also be configured to send signals indicative of the sensed temperature to the controller on a substantially continuous basis. The sensed temperature may be representative of the temperature of the catalyst materials at start-up of the power source 12 and/or during a prolonged low exhaust temperature operation of the power source 12. Upon receiving, for example, temperature information sent by the temperature sensor 48, the controller may store the information for further use. The controller may also manipulate the information in any conventional mathematical and/or statistical way, such as, for example, by entering the information into one or more preset algorithms used to control one or more components of the exhaust treatment system 100. For example, the controller may compare the sensed temperature to a predetermined threshold temperature (step 56). The threshold temperature may correspond, for example, to the light- off temperature of the catalyst materials disposed within the filter 36, and in an exemplary embodiment, the threshold temperature may be approximately 250 degrees Celsius. If the sensed temperature is above the predetermined threshold temperature, the exhaust treatment system 100 may continue to operate according to a steady state control strategy (step 58) stored within the controller. The steady state control strategy may apply to situations where, for example, the temperature of the catalyst materials within the filter 36 is above the light-off temperature of the catalyst materials. If, on the other hand, the sensed temperature is below the predetermined threshold temperature, the controller may ignite the regeneration device 20 (step 60).

Igniting the regeneration device 20 may include a number of system verification processes, such as, for example, sensing the pressure and/or flow rate of the combustible substance and supply of oxygen being directed to the regeneration device 20 for combustion, and substantially blocking a flow of recirculated exhaust gas from entering the mixing valve 30 (and, thus, from entering the inlet 21 of the power source 12). Igniting the regeneration device 20 may also include, for example, energizing the ignitor, injecting the combustible substance, and regulating the supply of oxygen passing to the regeneration device 20.

Once the regeneration device 20 has been ignited, the regeneration device 20 may be controlled to operate at a target temperature (step 62). The target temperature may correspond to the minimum temperature setting of the regeneration device 20 and may be within a peak conversion efficiency range of the catalyst materials. For example, in an embodiment of the present disclosure, the target temperature may be between approximately 300 degrees Celsius and approximately 350 degrees Celsius. Operating the regeneration device 20 in this way may heat the exhaust gas flowing therethrough to the target temperature and may begin to increase the temperature of the catalyst materials of the filter 36 through convection and/or conduction. Accordingly, a temperature of the exhaust flow measured by a temperature sensor 49 disposed upstream of the catalyst materials should be equal to the target temperature.

The controller may also modify one or more control parameters of the exhaust treatment system 100 (step 64), and such modifications may approximate the control parameters utilized during regeneration of the filter 36. For example, the controller may modify the position and/or other settings of the mixing valve 30. Such modified settings may allow a flow of recirculated exhaust gas to once again enter the mixing valve 30, but may result in a relative decrease in the amount of recirculated exhaust gas being supplied to the inlet 21 of the power source 12 compared to the steady state control strategy discussed above. In an exemplary embodiment, the amount of recirculated exhaust gas being supplied to the inlet 21 may be reduced by as much as approximately 50 percent under these modified settings. The controller may also modify the timing of one or more intake valves (not shown) associated with the inlet 21 and may alter the boost level of the energy extraction assembly 22.

The temperature sensors 48, 49 may then be used to sense a temperature upstream and downstream of the catalyst materials (step 66). As discussed above, the temperature of the exhaust flow upstream of the catalyst materials may be raised to the target temperature by way of the regeneration device 20. Thus, the temperature sensed by temperature sensor 49 may be approximately equal to the target temperature. The temperature sensed by temperature sensor 48, on the other hand, may approximate the temperature of the catalyst materials and/or the filter 36, and may initially be less than a temperature sensed upstream thereof. The temperature sensors 48, 49 may send signals containing this sensed temperature information to the controller, and the controller may determine whether the temperature sensed downstream of the catalyst materials is greater than or equal to the target temperature (step 68).

If the temperature sensed downstream of the catalyst materials is less than the target temperature, the regeneration device 20 may be controlled to continue heating the exhaust gas to the target temperature, and the temperature sensors 48, 49 may continue to sense temperatures upstream and downstream of the catalyst materials (step 66). If, on the other hand, the temperature sensed downstream of the catalyst materials is greater than or equal to the target temperature, the controller may command the regeneration device 20 to continue burning at the target temperature for a predetermined period of time (step 70). The predetermined period of time may be any desirable length of time useful in ensuring that the entire substrate, mesh, and/or other structure on which the catalyst materials are disposed has substantially uniformly reached the target temperature. Holding the regeneration device 20 at the target temperature for the predetermined period of time may also substantially mitigate any errors in the sensed temperature values. In an exemplary embodiment of the present disclosure, the predetermined period of time may be 90 seconds. Once the predetermined period of time has expired, the regeneration device 20 may be turned off (step 72) and the control parameters of the exhaust treatment system 100 that were modified in step 62 may be reset to the values, positions, and/or settings that were operative at start-up (step 74). The values, positions, and/or settings of the control parameters selected in step 74 may be substantially the same as those utilized by the steady state control strategy of step 58.

Controlling the components of the exhaust treatment system 100 in this way may assist in reducing, for example, the particulate matter emissions of the power source 12. In particular, rapidly increasing the temperature of the catalyst materials disposed within the exhaust treatment system 100 to at least their light-off temperature may assist in reducing hydrocarbon emissions of the power source 12 at start-up. As discussed above, once the catalyst materials reach their light-off temperature, the catalyst materials may oxidize substantially all of the hydrocarbon present in an exhaust flow of the power source 12, thereby reducing the amount of harmful pollutants released to the environment and minimizing the levels of whitesmoke and undesirable odors emitted by the exhaust treatment system 100. Other embodiments of the disclosed exhaust treatment systems 10,

100 will be apparent to those skilled in the art from consideration of the specification. For example, the systems 10, 100 may include additional filters, such as, for example, a sulfur trap disposed upstream of the filter 36. The sulfur trap may be useful in capturing sulfur molecules carried by the exhaust flow. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.

Claims

1. A method of controlling an exhaust treatment system (10, 100), comprising: sensing a temperature representative of a catalyst material temperature at start-up of a power source (12); comparing the sensed temperature to a threshold temperature; igniting a regeneration device (20) of the exhaust treatment system (10, 100) in response to the comparing, the regeneration device (20) being disposed upstream of the catalyst material; and operating the regeneration device (20) at a target temperature.

2. The method of claim 1, further including modifying a control parameter of the exhaust treatment system (10, 100) in response to the comparing.

3. The method of clam 2, wherein modifying the control parameter includes modifying at least one of a position of a mixing valve (30), a timing of an intake valve associated with the power source (12), and a boost level of an energy extraction assembly (22).

4. The method of claim 1, further including sensing a first temperature at a location upstream of the catalyst material and a second temperature at a location downstream of the catalyst material.

5. The method of claim 4, further including comparing the first temperature to the second temperature and operating the regeneration device (20) at the target temperature for a predetermined period of time in response to the comparison between the first and second temperature.

6. The method of claim 1, further including turning off the regeneration device (20) and modifying a control parameter of the exhaust treatment system (10, 100).

7. The method of claim 1, wherein the threshold temperature is a light-off temperature of the catalyst material.

8. An exhaust treatment system (10, 100) of a power source (12), comprising: a catalyst material; a regeneration device (20) disposed upstream of the catalyst material and configured to increase a temperature of the catalyst material to a target temperature at start-up of the power source (12) and in response to a sensed parameter of the exhaust treatment system (10, 100); and a particulate filter (16, 36) configured to extract components from an exhaust flow of the power source (12).

9. The system of claim 8, wherein the sensed parameter of the exhaust treatment system (10, 100) is a temperature representative of the catalyst material at start-up of the power source (12).

10. The system of claim 8, the target temperature is between approximately 300 degrees Celsius and approximately 350 degrees Celsius.