Patent Application
20200003103
The present disclosure relates to an exhaust aftertreatment system for an engine. More particularly, the present disclosure relates to an exhaust aftertreatment system for an engine that is configured to operate under a range of stoichiometric and sub-stoichiometric air-fuel ratios (0.92<λ≤1).
An aftertreatment system may be provided for reducing an amount of undesired emissions, for example, Carbon monoxide (CO), Nitric oxides (NOx), or excess Ammonia (NH3) that could be present in an exhaust of an internal combustion engine. Use of the aftertreatment system can therefore help render the exhaust innocuous from one or more obnoxious constituents, that would otherwise negatively impact the atmosphere besides being detrimental to plant and animal life.
However, many limitations in the performance of these aftertreatment systems may arise owing, at least in part, due to system design. In many cases, it has been seen that when two or more catalysts, for instance, a Three-Way Catalyst (TWC), a Diesel Oxidation Catalyst (DOC), and/or an Ammonia Slip Catalyst are to be included in an aftertreatment system, the catalysts received the exhaust serially, however these catalysts were typically positioned in line with one another, or stated differently, one behind the other.
With such inter-relative positioning of these catalysts, the aftertreatment system would be rendered bulky and consequently entail a large packaging space. This would also pose challenges during installation of the aftertreatment system when tight space constraints are encountered. Moreover, by positioning these catalysts one behind the other, it is also envisioned that the individual catalysts may suffer from successive drops in temperature as the gas is flown past each of these catalysts and consequently, one or more of these catalysts may require a longer time to ‘light-off’.
U.S. Pat. No. 6,837,336 (hereinafter referred to as ‘the '336 patent’) discloses an apparatus that includes a plurality of gas treating compartments. In each of these compartments, a tubular body member containing a treatment element may be present. Although not disclosed by the '336 patent, it can be believed that the tubular shape of the body members and the inter-relative positioning of these body members disclosed in the '336 patent could hold promise in overcoming the afore-mentioned drawbacks.
Nevertheless, ever stringent emission regulations have also been driving manufacturers of aftertreatment devices to continually direct their efforts towards improving a conversion efficiency of the aftertreatment devices. Hence, there is a need for an exhaust aftertreatment system that provides an improved conversion efficiency for reducing the negative impact that may be caused to the atmosphere, plant life, or animal life from combustion of fuels.
In an embodiment of the present invention, an exhaust aftertreatment system for an engine operating within a range of stoichiometric and sub-stoichiometric air-fuel ratios (0.92<λ≤1) includes an exhaust passageway, and a first catalytic module that has an inlet disposed in fluid communication with the exhaust passageway for receiving exhaust from the exhaust passageway. The exhaust aftertreatment system also includes a first device for introducing an oxidant into the exhaust of the first catalytic module, and a second device for mixing the introduced oxidant with the exhaust of the first catalytic module. The exhaust aftertreatment system also includes a second catalytic module concentric with the first catalytic module such that heat transfer is facilitated between the first and second catalytic modules while exhaust is prevented from flowing radially between the first and second catalytic modules, and a means for diverting the exhaust from an outlet of the first catalytic module to an inlet of the second catalytic module.
In an embodiment of the present invention, the inlet of the first catalytic module may be coupled to an outlet of a conduit defining the exhaust passageway. In one embodiment, the inlet of the first catalytic module is joined with the outlet of the conduit by an adhesive. In an alternative embodiment of the present invention, the inlet of the first catalytic module may be joined with the outlet of the conduit using a compressible fiber mat. Additionally, or optionally, a compression seal could be positioned between the inlet of the first catalytic module and the outlet of the conduit.
In an embodiment of the present invention, the inlet of the first catalytic module may be positioned proximal to an outlet of a conduit defining the exhaust passageway. For instance, the inlet of the first catalytic module could be positioned within a range of 3 to 10 millimeters from the outlet of the conduit. Also, a diameter of the inlet of the first catalytic module could be equal to or greater than a diameter associated with the outlet of the conduit.
In an embodiment of the present invention, the first catalytic module may be formed from a first substrate and the second catalytic module may be formed from a second substrate. Further, an impermeable member could be positioned between the first and second substrates for preventing the exhaust from flowing radially between the first and second catalytic modules. Furthermore, a co-efficient of thermal expansion associated with the impermeable member could be selected to lie within a predetermined range of, or be similar to, a co-efficient of thermal expansion associated with at least one of the first and second substrates.
In an alternative embodiment of the present invention, the first and second catalytic modules may be formed from a monolithic substrate defining a plurality of channels therethrough. The first and second catalytic modules may be separated by an impermeable zone defined in an annular region of the monolithic substrate.
Further, in one embodiment of the present invention, the impermeable zone could be formed integrally with the monolithic substrate by rendering the annular region of the monolithic substrate between the first and second catalytic modules with zero porosity. In an alternative embodiment of the present invention, the impermeable zone may be formed by plugging ends of channels in the annular region of the monolithic substrate with an inert non-catalytic solid. In yet another alternative embodiment, the impermeable zone could be defined by filling channels in the annular region of the monolithic substrate with an inert non-porous medium.
In an embodiment of the present invention, the exhaust aftertreatment system may include a housing. The housing may have a first end and a second end that is distally located from the first end. The first catalytic module could be positioned within the housing such that the inlet of the first catalytic module is disposed proximal to the first end of the housing. In one further embodiment, the means for diverting the exhaust from the outlet of the first catalytic module to the inlet of the second catalytic module may be the second end of the housing. Also, the second device may be positioned at, or adjacent to the second end of the housing so that the exhaust is mixed with introduced oxidant prior to the oxidant enriched exhaust entering the second catalytic module.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.
This disclosure relates to an exhaust aftertreatment system for an engine. More particularly, the present disclosure relates to an exhaust aftertreatment system for an engine that is configured to operate under a range of stoichiometric and sub-stoichiometric air-fuel ratios (0.92<λ≤1).
Referring to
The engine 102 may be, for example, a spark-ignited (SI) engine, or a compression ignited (CI) engine. The engine 102 may be a single cylinder engine, or a multi-cylinder engine. Where the engine 102 is of a spark-ignited type, fuel that would be associated with the engine 102 may include, but is not limited to, Gasoline (Petrol), Compressed Natural Gas (CNG), Autogas (Liquified Petroleum Gas (LPG)), methanol, ethanol, bioethanol, hydrogen, or other spark-ignited fuels known to persons skilled in the art. Where the engine 102 is of a compression ignited type, a type of fuel may include, for example, diesel.
Although some examples of engines may be disclosed herein, it may be noted that such examples are not limiting of a configuration, or a fuel-type associated therewith. Rather, it will be appreciated that aspects of the present disclosure may be adapted to suit different engine and exhaust aftertreatment system configurations depending on specific requirements of an application. In fact, aspects of the present disclosure are directed towards improving a conversion efficiency of an aftertreatment system that is provided for treating exhaust that is produced under stoichiometric and sub-stoichiometric engine operation i.e., where λ is between 0.92 and 1 but not exceeding 1.
As shown, the engine 102 is provided with an exhaust aftertreatment system 104. In the illustrated embodiment of
As shown, the exhaust aftertreatment system 104 further includes an exhaust passageway 112. The exhaust passageway 112 is defined by a conduit 114 that may form part of the engine 102, or the exhaust aftertreatment system 104. The exhaust aftertreatment system 104 also includes a first catalytic module 116. The first catalytic module 116 may be, for example, a three-way catalytic converter (TWC). The first catalytic module 116 is positioned within the housing 106, and has an inlet 118 that, as shown in the illustrated embodiment of
The inlet 118 of the first catalytic module 116 is also disposed in fluid communication with the exhaust passageway 112 for receiving exhaust of the engine 102 from the exhaust passageway 112. As shown in the illustrated embodiment of
As shown in the illustrated embodiment of
Additionally, or optionally, a compression seal 124 could be positioned between the outlet 120 of the conduit 114 and the inlet 118 of the first catalytic module 116. The compression seal 124 would be configured to prevent a loss of fluid communication between the outlet 120 of the conduit 114 and the inlet 118 of the first catalytic module 116.
Further, as shown, the exhaust aftertreatment system 104 also includes a first device 126 for introducing an oxidant 128 into the exhaust of the first catalytic module 116. In certain embodiments, the first device 126 may be a passively operational device, for example, an opening 130 that is in fluid communication with a portion of the housing 106 adjacent the second end 110 of the housing 106 as shown in the illustrated embodiment of
Furthermore, the exhaust aftertreatment system 104 also includes a second device 132 for mixing the introduced oxidant with the exhaust of the first catalytic module 116. The second device 132 may be a gas mixer, preferably, of a configuration that can be accommodated and secured within the housing 106.
In embodiments herein, although it is disclosed that the exhaust aftertreatment system 104 includes the first device 126 and the second device 132 as separate devices for performing specific functions, it other embodiments of the present invention, it can be contemplated to incorporate a single device that provides the functionality disclosed in conjunction with respective ones of the first device 126 and second device 132. Such modifications are to be understood as falling within the scope of the present invention.
The exhaust aftertreatment system 104 also includes a second catalytic module 134. The second catalytic module 134 may include one or more of, for example, a Diesel Oxidation Catalyst (DOC), an Ammonia Slip Catalyst (ASC), a Diesel Particulate Filter (DPF) or other types of catalysts known to persons skilled in the art. The second catalytic module 134 is concentric with the first catalytic module 116 such that heat transfer is facilitated between the first and second catalytic modules 116, 134 while exhaust is prevented from flowing radially between the first and second catalytic modules 116, 134.
With continued reference to
In a further embodiment, the second device 132 may be positioned at, or adjacent to the second end 110 of the housing 106 so that the exhaust is mixed with introduced oxidant prior to the oxidant enriched exhaust entering the inlet 140 of the second catalytic module 134.
In one embodiment as shown in
In an embodiment as shown by way of the diagrammatic sectional representation in
Also, it is hereby contemplated that a type of material used to form the impermeable member 146 may be, preferably, non-catalytic in nature to respective ones of the reactions occurring in each of the first and second catalytic modules 116, 134. In one example, the impermeable member 146 could be embodied as a can or a shell made from Stainless Steel (SS), or other suitable alloys of steel having a grade that would meet specific requirements of the aftertreatment application.
Furthermore, a co-efficient of thermal expansion associated with the impermeable member 146 could be selected to lie within a predetermined range, for example, within 10 percent tolerance, from a co-efficient of thermal expansion associated with at least one of the first and second substrates 142, 144. It is envisioned that with little or no difference between the co-efficient of thermal expansions of respective ones of the first substrate 142, the second substrate 144, and the impermeable member 146, uniform expansion may be experienced to minimize a possibility of the exhaust aftertreatment system's structural integrity from being compromised, for example, by cracking under the effect of non-uniform expansion during operation.
In another embodiment as shown in
In an alternative embodiment as shown in
In one embodiment as shown in
Various embodiments disclosed herein are to be taken in the illustrative and explanatory sense and should in no way be construed as limiting of the present disclosure. All joinder references (e.g., attached, joined, coupled, connected, and the like) are only used to aid the reader's understanding of the present disclosure, and may not create limitations, particularly as to the position, orientation, or use of the systems disclosed herein. Therefore, joinder references, if any, are to be construed broadly. Moreover, such joinder references do not necessarily infer that two elements are directly connected to each other.
Additionally, all numerical terms, such as, but not limited to, “first”, “second” or any other ordinary and/or numerical terms, should also be taken only as identifiers, to assist the reader's understanding of the various elements of the present disclosure, and may not create any limitations, particularly as to the order, or preference, of any element relative to, or over, another element.
It is to be understood that individual features shown or described for one embodiment may be combined with individual features shown or described for another embodiment. The above described implementation does not in any way limit the scope of the present disclosure. Therefore, it is to be understood although some features are shown or described to illustrate the use of the present disclosure in the context of functional devices, such features may be omitted without limiting the scope of the present disclosure as defined by the appended claims.
The terms ‘fuel dithering’, describe an oscillation of an engine charge composition relating to different Lambda (λ i.e., normalized air-fuel ratio) values over time. Fuel dithering, when implemented, by dynamically operating engine fuel supply systems, can create consecutive patterns of rich/lean fueling conditions in the engine that, in turn, can lead to dynamically oscillating catalyst surface conditions in an exhaust aftertreatment system to achieve an optimum conversion efficiency.
Although many fuel dithering techniques are known to persons skilled in the art, aspects of the present disclosure have been discussed independent of such fuel dithering techniques. As aspects of the present disclosure are also directed at improving a conversion efficiency of an aftertreatment system, it will be appreciated that aspects of the present disclosure can be implemented to realize an improved conversion efficiency in conjunction with, or without the implementation of a fuel dithering technique.
With use of embodiments disclosed herein, manufacturers can render exhaust aftertreatment systems with a compact configuration and an improved conversion efficiency. In embodiments herein, by positioning the first and second catalytic modules 116, 134 concentrically, an axial length of the housing 106 may decrease, and this decrease in the axial length of the housing 106 may help render a compact configuration to the exhaust aftertreatment device 104. As the compact configuration of the exhaust aftertreatment system 104 also serves to reduce an overall space claim, packaging requirements for the exhaust aftertreatment system 104 of the present invention may be minimized and the exhaust aftertreatment system 104 can be installed in locations that have tight space constraints.
Moreover, as the first and second catalytic modules 116, 134 are placed concentrically, the exhaust would be required to pass through the first catalytic module 116, mix with the oxidant 128, cause to be reversed in its direction of flow, and thereafter be treated as an oxidant enriched mixture at the second catalytic module 134 before exiting the housing 106. It may be noted that if the first catalytic module 116 embodies, for instance, a three-way catalyst (TWC), then the first catalytic module 116 could abate most of the undesired constituents in the exhaust stream i.e., reduce Nitrogen oxides (NOx) to Nitrogen (N2), oxidize Carbon monoxide (CO) to Carbon dioxide (CO2), and oxidize unburnt hydrocarbons (HC) to Carbon dioxide (CO2) and water (H2O).
Also, it is hereby contemplated that in some cases, a third device (not shown) could also be provided with the exhaust aftertreatment system 104 of the present invention to dose a reductant, for example, Urea typically in the form of an aqueous Ammonia (NH3) solution. It is hereby envisioned that this Ammonia (NH3), if present in excess quantities, and if traces of the undesired constituents (NOx, CO, and/or unburnt hydrocarbons) continue to remain, then by introducing the oxidant 128, preferably, under pressure, and subsequently mixing the exhaust of the first catalytic module 116 with the oxidant 128, a concomitant abatement of remnant Nitrogen oxides (NO), Carbon monoxide (CO), unburnt hydrocarbons (HC), and any excess Ammonia (NH3) could be easily achieved.
Moreover, it is hereby also envisioned that by reversing the flow of the oxidant enriched exhaust towards the second catalytic module 134, an increased amount of residence time would be available for the exhaust of the first catalytic module 116 in the housing of the exhaust aftertreatment system 104 so that the exhaust can be abated of its undesired constituents. Due to this, a reduction in the amount of the undesired constituents would be enhanced as compared to that accomplished with use of previously known aftertreatment systems. Therefore, with use of embodiments herein, a conversion efficiency of the aftertreatment system disclosed herein may be greater than that typically associated with use of previously known aftertreatment systems resulting in an improved abatement of the undesired emissions in the exhaust, and lesser detrimental effects to the atmosphere.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems, methods and processes without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
