Patent Application
20080053071
Combustion chamber 30 may receive intake air from intake passage 44 via intake manifold 42 and may exhaust combustion gases via exhaust passage 48. Intake passage 44 and exhaust passage 48 can selectively communicate with combustion chamber 30 via respective intake valve 52 and exhaust valve 54. In some embodiments, combustion chamber 30 may include two or more intake valves and/or two or more exhaust valves.
Fuel injector 66 is shown coupled directly to combustion chamber 30 for injecting gasoline or diesel fuel directly therein in proportion to the pulse width of signal FPW received from controller 12 via electronic driver 68. In this manner, fuel injector 66 provides what is known as direct injection of fuel into combustion chamber 30. The fuel injector may be mounted in the side of the combustion chamber or in the top of the combustion chamber, for example. Fuel may be delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, a fuel pump, and a fuel rail. In some embodiments, combustion chamber 30 may alternatively or additionally include a fuel injector arranged in intake passage 44 in a configuration that provides what is known as port injection of fuel into the intake port upstream of combustion chamber 30.
Intake manifold 42 may include a throttle 62 having a throttle plate 64. In this particular example, the position of throttle plate 64 may be varied by controller 12 via a signal provided to an electric motor or actuator included with throttle 62, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle 62 may be operated to vary the intake air provided to combustion chamber 30 among other engine cylinders. The position of throttle plate 64 may be provided to controller 12 by throttle position signal TP. Intake manifold 42 may include a mass air flow sensor 120 and a manifold air pressure sensor 122 for providing respective signals MAF and MAP to controller 12.
Ignition system 88 can provide an ignition spark to combustion chamber 30 via spark plug 92 in response to spark advance signal SA from controller 12, under select operating modes. Though spark ignition is shown in
Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstream of emission control device 70. Sensor 126 may be any suitable sensor for providing an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor.
Aftertreatment device 70 is shown arranged along exhaust passage 48 downstream of exhaust gas sensor 126 where in aftertreatment device 70 may be a three way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof as to be detailed further in
Controller 12 is shown in
Controller 12 may determine various conditions of aftertreatment device 70 and SCR catalytic converter 74 in any suitable manner. For example, the temperature Tatd of aftertreatment device 70 may be provided by a temperature sensor 72 and the temperature Tcat of SCR catalytic converter 74 may be provided by a temperature sensor 76. In addition, sensor 110 provides an indication of both the oxygen concentration in the exhaust gas as well as NOx concentration. Signal 112 provides controller 12 a voltage indicative of the O2 concentration while signal 114 provides a voltage indicative of NOx concentration. Under some conditions, controller 12 may be configured to provide a rich exhaust stream based on various conditions, such as NOx concentration downstream of SCR catalytic converter 74.
As described above,
The aftertreatment device and the SCR catalytic converter may be arranged in various configurations. In the embodiment described herein, the SCR catalytic converter may be arranged downstream from the aftertreatment device. By doing this, NH3 that may be generated by the aftertreatment device under some conditions may be used as the reductant in the SCR catalytic converter for the selective and catalytic reduction of NOx leaving the aftertreatment device.
Referring back to
The aftertreatment device may facilitate the storage of NOx and the reduction of stored NOx to N2 or NH3 or some combination thereof. In the embodiment described herein, it may be desirable to substantially convert stored NOx to NH3 such that NH3 leaving the aftertreatment device may be adsorbed in the SCR catalytic converter wherein the adsorbed NH3 may reduce NOx exiting the aftertreatment device.
The aftertreatment device may include a first catalyst region 210 and a second catalyst region 220 wherein the first catalyst region may be upstream of the second catalyst region. The catalyst regions may include one or more components dispersed on a support wherein a catalyst region may be disposed on a substrate, such as a ceramic or metal honeycomb monolith.
The components and support may further include one or more elements or compounds or some combination thereof. For example, a precious metal component may include the element Pt, a NOx sorbent component may include the compound barium oxide (BaO), and a support may include the compound alumina (Al2O3).
Further, a component as well as the support may exhibit various properties under some conditions. For example, a property of a precious metal component, such as Pt, may be to catalyze the oxidation and storage of NOx. A property of a NOx sorbent component, such as BaO, may be NOx storage when catalyzed at high temperature ranges. A property of a refractory metal oxide support, such as Al2O3, may also be NOx storage but when catalyzed at low temperature ranges. Another property of a precious metal component, such as Pt, may be to catalyze the preferential conversion of stored NOx to NH3 during rich excursions.
Accordingly, one exemplary embodiment of the catalyst regions for the components and support described herein (e.g., Pt, BaO, and Al2O3) may include a precious metal component (e.g., Pt) and a support (e.g., Al2O3) for the first catalyst region 210 and a precious metal component (e.g., Pt), a NOx sorbent component (e.g., BaO), and a support (e.g., Al2O3) for the second catalyst region 220, wherein the precious metal component may include at least one precious metal element (e.g., Pt), the NOx sorbent component may include at least one suitable alkali or alkaline earth compound (e.g., BaO), and the support may include at least one suitable refractory metal oxide (e.g., Al2O3).
The properties of the catalyst regions may relate to the properties of the components and the support included therein. However, the components and the support in the catalyst region may interact such that the aggregate properties of the components and the support included therein may be distinct for the properties of the catalyst region. In particular, the properties of the components and the support included in the catalyst region may be diluted by various other components included therein.
For example, the first catalyst region having a precious metal component may have no constituents of a NOx sorbent component (e.g., it may be substantially pure of NOx sorbent components, for example the precious metal component may be Pt), and may exhibit properties that may include catalyzing the oxidation and storage of NOx on the Al2O3 support at low temperatures. However, the precious metal component may be at least partially deactivated by the presence, or an increased amount, of a NOx sorbent component, such as BaO. As such, the contaminated precious metal component may less able to abate NOx at low temperatures.
For the aftertreatment device described herein, the catalyst regions may include a precious metal component and a NOx sorbent component wherein the ratio of the precious metal component to the NOx sorbent component may be greater in one catalyst region than the ratio in another catalyst region from which it is physically segregated, where the region with a higher ratio may be located upstream of the region with a lower ratio. Likewise, the catalyst regions may include a precious metal component and a NOx sorbent component wherein the amount or weight of the NOx sorbent component may be greater in one catalyst region than in another catalyst region from which it is physically segregated, where the region with a higher amount of NOx sorbent may be located downstream of the region with a lower amount (or substantially no) NOx sorbent.
In one particular embodiment, it may be advantageous to distribute the components such that the components may be disposed in the aftertreatment device such that the ratio of the precious metal component to the NOx sorbent component may be greater in the first catalyst region than the ratio in the downstream second catalyst region from which it is physically segregated. By doing this, the first catalyst region including a relatively higher percent of the precious metal may be exposed to the exhaust when the concentration of NOx may be the greatest (e.g. as the exhaust from the engine enters the emission treatment system). As such, the amount of NOx stored and subsequently converted to NH3 for the SCR catalytic converter may be increased. Conversely, the components may be disposed in the aftertreatment device such that the ratio of the precious metal component to the NOx sorbent component may be less in the first catalyst region than said ratio in the upstream second catalyst region for various other reasons.
Referring back to the embodiment illustrated in
The area of separation may employ various approaches or structures to segregate the catalyst regions. For example, the area of separation may include a divider wherein the divider may include suitable materials capable of at least partially segregating the catalyst regions while facilitating suitable exhaust flow. In another example, the area of separation may be a void wherein a void of some distance segregates the catalyst regions. In another embodiment of the aftertreatment device segregated washcoat may be used to configure the catalyst regions. Further, the area of separation may be configured perpendicular or parallel or to various other degrees relative to the exhaust flow.
As noted herein, the aftertreatment device may store NOx and reduce stored NOx into N2 or NH3. In the embodiment described herein, it may be desirable to substantially convert NOx to NH3 such that NH3 leaving the aftertreatment device may be adsorbed in the SCR catalytic converter wherein the adsorbed NH3 may reduce NOx exiting the aftertreatment device. Conversely, in another approach, a NOx abatement device may include catalyst regions wherein the components of the catalyst may not form relatively high amounts of NH3 or at least one component of the catalyst may hinder NH3 generation, although some NH3 may be generated. For example, some NOx abatement devices may include an oxygen storage component (OSC) such as ceria (CeO2) wherein the CeO2 component may limit the formation of NH3. The CeO2 component may be used for various other reasons, such as improving low temperature NOx conversion, and also the intermittent storage of oxygen.
Referring back to graph 300, the exclusion of the CeO2 component in the catalyst region may convert a higher percentage of NOx to NH3 at a wider temperature range relative to the catalyst that includes a CeO2 component. As such, it may be beneficial under some conditions to exclude the CeO2 component from one or more catalyst regions, such as region 210, 220, or both. By doing this, the aftertreatment device may generate sufficient NH3 such that a liquid urea tank or ammonia storage vessel may be excluded from the emission treatment system described herein. However, the liquid tank may also be included, if desired.
The inclusion of the CeO2 component in the Pt—BaO catalyst composition may convert at least partially higher percentage of NOx to NH3 at lower temperatures, although the percentage of NOx converted to NH3 may still not be sufficient for low temperature ranges. As such, it may be desirable to include at least a component such as Pt—BaO substantially or at least partially free of CeO2 so as to generate higher NH3 amounts over a wider temperature range and at least another component that may facilitate at least sufficient NH3 generation at a lower temperature range.
The NOx that may not react to form NH3 may be converted by various other mechanisms or may not be stored or converted and exit the aftertreatment device. The percentage of the NOx that may react to form NH3 or other products by various mechanisms or some combination thereof may be referred to cumulatively as the percentage of total NOx conversion. Specifically, the percentage of total NOx conversion may include the intermittent conversion of NOx in a catalyst region for storage or the reduction of NOx to N2 or the formation of NH3 from NOx or a variety of other mechanisms of NOx conversion or some combination thereof.
While it may be advantageous to convert a substantial percentage of NOx to NH3 to use as a reductant in the SCR catalytic converter, the emission system described herein may further benefit by converting the residual NOx not used to generate NH3. By doing this, a more modest amount of NH3 may be suitable to substantially reduce the NOx in the SCR catalytic converter. Even further, the NOx that may be stored in a catalyst region in the aftertreatment device may be utilized to generate additional NH3 under some conditions, such as the exhaust composition. As such, a high percentage of total NOx conversion may be advantageous to facilitate the optimization of NOx abatement, as will be described further with regard to
While the inclusion of CeO2 in the catalyst compositions may convert a higher percentage of total NOx, NH3 generation may still be insufficient for the emission treatment system described herein. As such, it may be desirable to include a precious metal component and a NOx sorbent component such as Pt—BaO in one catalyst region so as to facilitate NH3 generation and NOx conversion over a relatively wider higher temperature range (
While the exclusion or reduction of a NOx sorbent component such as BaO in an upstream region, such as 210, may facilitate low temperature NOx conversion, NOx conversion at higher temperature ranges may be substantially reduced. As such, it may be desirable to combine the properties of a catalyst region that that may exhibit the NOx conversion properties a precious metal and NOx sorbent catalyst region (e.g., NH3 generation and total NOx conversion over a relatively wider higher temperature range) such as Pt—BaO and the properties of a catalyst region that may exhibit properties of a region with precious metals having less NOx sorbent materials (e.g., low temperature NOx conversion) such as Pt—Rh as demonstrated by
The combination of a Pt—Rh catalyst region (substantially free of CeO2) physically segregated and upstream of a Pt—BaO catalyst region (also substantially free of CeO2) is one exemplary embodiment of a combination that may be included in the aftertreatment device. Various other suitable ceria and non-ceria combinations of components may be used. In general, the catalyst regions may include at least a first precious metal component wherein a precious metal component may include one or more precious metals (e.g. Pt, Pd, Rh, Ir, Ru, Os, Re, Ag, and Au) wherein precious metals include PGMs (e.g., Pt, Pd, Rh) with a first amount of a NOx sorbent (which may be zero) and at least a second precious metal component with a second amount of the NOx sorbent component, where the second amount is greater than the first amount and where a NOx sorbent component may include one or more NOx sorbents, such as an oxide or carbonate of an alkali metal (e.g. Li, Na, K, Rb, Cs) or an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba,), or some combination thereof. The above components may be dispersed on a high surface area metal oxide support (e.g., alumina, titania, zirconia, zeolites, etc), such that the first support is a metal oxide that may store NOx (e.g., alumina or zeolite). The components and their support typically are disposed on a monolithic flow-through substrate, wall flow filter substrate, honeycomb structures, layered materials, or spun fibers, among other configurations.
In one approach, the first precious metal component may be blended with the second precious metal component and the NOx sorbent component wherein the blend may be housed in at least one catalyst region. However, the function of some components may be reduced or deactivated in the presence of other components. For example, the NOx sorbent component may reduce the activity of precious metal components such that higher temperatures may be required to achieve suitable levels of NOx conversion. Said another way, the first precious metal component may convert substantially less NOx at lower temperatures in the presence of the NOx sorbent component.
In the embodiment described herein, the first precious metal component may be physically segregated from the NOx sorbent component to address the deactivation of the precious metal component by the NOx sorbent component. In particular, the first precious metal component may be disposed in one catalyst region and the second precious metal component with the NOx sorbent may be disposed in another catalyst region wherein the catalyst regions may be segregated by various modes as described herein.
Generally, the physical segregation of the catalyst regions within the aftertreatment device may facilitate various mechanisms wherein at least one catalyst region may promote the formation of NH3 from NOx (e.g., adsorbed NOx or NOx in the exhaust) or the reduction of stored NOx to N2 or some combination thereof during rich excursions and one catalyst region may promote the storage of NOx during lean operation.
Referring back to
In the embodiment described herein, rich excursions may include a condition wherein a reducing agent (e.g. hydrocarbons from fuel not combusted in the engine, injected fuel, etc.) may be present in the exhaust and relatively low concentrations of NOx may be detected, while lean operation may include a condition wherein NOx and excess oxygen may be abundant in the exhaust.
The flowcharts are a conceptual representation that may be simplified for clarity.
Referring specifically to
At 630, NOx may be reduced to NH3 or reduced to N2 or some combination thereof in the aftertreatment device. The aftertreatment device as described herein may promote the conversion of a relatively high percentage of NOx to NH3, although some NOx may be reduced to N2 wherein the reducing agent may include HC in the exhaust. The NOx may be adsorbed in the aftertreatment device during lean operation or may enter with the exhaust or some combination thereof. The NH3 generated at the aftertreatment device may proceed to a downstream SCR catalytic converter accordingly. Continuing with the figure of 6A, the NH3 entering the SCR catalytic converter may substantially adsorb the NH3 at 640.
Referring now to
The emission control system may be regulated by the controller to follow the above approaches. In particular, the controller may facilitate the release of NOx and/or NH3 from the aftertreatment device to the SCR catalytic device during various conditions by adjusting fuel injection, engine airflow, or combinations thereof. For example, it may be advantageous to end a rich excursion and initiate lean operation when the SCR catalytic converter may be approaching the threshold capacity of NH3 adsorption. At this condition, the controller may prompt lean operation in response to a signal from a sensor (e.g., oxygen sensor, NOx sensor, NH3 sensor, etc.), for example, at the SCR catalytic converter. By doing this, NOx abundant in the exhaust during lean operation may be reduced by the NH3 saturated in the SCR catalytic converter.
Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The specific routines described herein may represent one or more of any number of methoding strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps, operations, or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of methoding is not necessarily required to achieve the features and advantages of the example embodiments described herein, but are provided for ease of illustration and description. One or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. Further, the described steps may graphically represent code to be programmed into the computer readable storage medium in the engine control system.
It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
