Patent Application
20110146252
The present disclosure is directed to an aftertreatment module and, more particularly, to a canister-type aftertreatment module.
Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
In order to comply with the regulation of NOX, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is a process where a reductant, most commonly urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and absorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOX in the exhaust gas to form water (H2O) and diatomic nitrogen (N2).
In some applications, the substrate used for SCR purposes may need to be very large to help ensure it has enough surface area or effective volume to absorb appropriate amounts of the ammonia required for sufficient reduction of NOX. These large substrates can be expensive and require significant amounts of space within the exhaust system. In addition, the substrate must be placed far enough downstream of the injection location for the urea solution to have time to decompose into the ammonia gas and to evenly distribute within the exhaust flow for the efficient reduction of NOX. This spacing may further increase packaging difficulties of the exhaust system.
An exemplary SCR-equipped system for use with a combustion engine is disclosed in JP Patent Publication No. 2008/274,851 (the '851 publication) of Makoto published on Nov. 13, 2008. This system includes an exhaust gas purification device having a gas accumulation canister, a separate dispersion canister, and a mixing pipe connected between edges of the gas accumulation and gas dispersion canisters. A particulate filter and an oxidation catalyst are disposed in the gas accumulation canister, while an SCR catalyst and ammonia reduction catalyst are disposed within the gas dispersion canister. A urea injector is located in the mixing pipe, upstream of the SCR catalyst.
Although compact in size, the exhaust system of the '851 patent may still be problematic. In particular, the multiple canisters used in the '851 system may increase component cost, packaging complexity, and an overall size of the system. In addition, the single SCR catalyst may be large and drive up the cost of the system.
The aftertreatment module of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.
One aspect of the present disclosure is directed to an aftertreatment module. The aftertreatment module may include a canister, and a wall disposed within the canister and axially-dividing the canister into a first portion and a second portion. The aftertreatment module may also include a first treatment device disposed within the first portion, an inlet connected to the first portion, a second treatment device disposed within the second portion, an outlet connected to the second portion, and an external tube extending from the first portion to the second portion.
A second aspect of the present disclosure is directed to another aftertreatment module. This aftertreatment module may include a canister, a first treatment device located in the canister at a first end portion of the canister, and a second treatment device located in the canister at an opposing second end portion of the canister. The aftertreatment module may also include an inlet physically-located between the first and second treatment devices and upstream of both the first and second treatment devices, and an outlet physically-located between the first and second treatment devices and downstream of both the first and second treatment devices.
A third aspect of the present disclosure is directed to yet another aftertreatment module. This aftertreatment module may include a canister having an inlet at a first end and an outlet at a second opposing end. The aftertreatment module may also include an external tube connected to the inlet and having a serpentine shape with a total flow length multiple times a flow length of the canister. The external tube may be contained within an axial length dimension of the canister. The aftertreatment module may further include a first treatment device disposed within the external tube, and a second treatment device disposed within the canister.
An exemplary aftertreatment module 10 is shown in
An external tube 24 may fluidly communicate first portion 20 with second portion 22. In one embodiment, external tube 24 may be axially-parallel with canister 12, and connect to a cylindrical side surface of canister 12 at opposing ends by way of flexible couplings 26. Flexible couplings 26 may embody cobra-head type couplings that are capable of bending through an angle of about 90 degrees and have an elliptical opening at canister 12 and a circular opening at tube 24. Other types of couplings may be utilized, if desired.
Aftertreatment module 10 may also include one or more treatment devices located within a first end of first portion 20, and one or more treatment devices located within a second opposing end of second portion 22. For example, an oxidation catalyst 28 may be disposed within first portion 20, while a combined diesel particulate filter/SCR (CDS) catalyst 30 may be disposed within second portion 22. In one embodiment, an additional catalyst 32 may also be located within second portion 22, downstream of CDS catalyst 30. Catalyst 32 may include an upstream region 32A that functions as an SCR catalyst, and a downstream region 32B that functions as a cleanup catalyst, for example an ammonia reduction catalyst. In an alternative embodiment, catalyst 32 may be a dedicated cleanup catalyst (e.g., catalyst 32 may not provide SCR functionality). It is contemplated that, although requiring additional space within canister 12, CDS catalyst 30 may alternatively be replaced with a separate and dedicated particulate filter and SCR catalyst, if desired. A space 34 may be maintained at the opposing ends of canister 12, axially-outward of all treatment devices disposed therein, to act as manifolds that facilitate substantially equal distribution of exhaust across faces of the respective treatment devices to and from couplings 26 of external tube 24.
In the configuration described above, inlet 14 and outlet 16 may both be located physically-between the treatment devices within first and second portions 20, 22. Inlet 14 may be located upstream of all treatment devices. Outlet 16 may be located downstream of all treatment devices. Inlet 14 may be extend from canister 12 in a direction about opposite to an extension direction of outlet 16.
Oxidation catalyst 28 may be, for example, a diesel oxidation catalyst (DOC). As a DOC, oxidation catalyst 28 may include a porous ceramic honeycomb structure, a metal mesh, a metal or ceramic foam, or another suitable substrate coated with or otherwise containing a catalyzing material, for example a precious metal, that catalyzes a chemical reaction to alter a composition of exhaust passing through oxidation catalyst 28. In one embodiment, oxidation catalyst 28 may include palladium, platinum, vanadium, or a mixture thereof that facilitates a conversion of NO to NO2. In another embodiment, oxidation catalyst 28 may alternatively or additionally perform particulate trapping functions (i.e., oxidation catalyst 28 may be a catalyzed particulate trap such as a CRT or CCRT), hydro-carbon reduction functions, carbon-monoxide reduction functions, and/or other functions known in the art.
As described above, CDS catalyst 30 may be configured to perform particulate trapping functions. In particular, CDS catalyst 30 may include filtration media configured to remove particulate matter from an exhaust flow. In one embodiment, the filtration media of CDS catalyst 30 may embody a generally cylindrical deep-bed type of filtration media configured to accumulate particulate matter throughout a thickness thereof in a substantially homogenous manner. The filtration media may include a low density material having a flow entrance side and a flow exit side and be formed through a sintering process from metallic or ceramic particles. It is contemplated that the filtration media may alternatively embody a surface type of filtration media fabricated from ceramic foam, a wire mesh, or any other suitable material.
CDS catalyst 30 may also be configured to perform SCR functions. Specifically, the filtration media of CDS catalyst 30 may be fabricated from or otherwise coated with a ceramic material such as titanium oxide; a base metal oxide such as vanadium and tungsten; zeolites; and/or a precious metal. With this composition, decomposed reductant entrained within an exhaust flow passing through CDS catalyst 30 may be absorbed onto the surface and/or within of the filtration media, where the reductant may react with NOx (NO and NO2) in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). It is contemplated that CDS catalyst 30 may perform both particulate trapping and SCR functions throughout the media of CDS catalyst 30 or, alternatively, in serial stages, as desired.
As described above, catalyst 32 may comprise an upstream region 32A and a downstream region 32B. In particular, a single substrate brick of catalyst 32 may include a region (32A) located generally upstream that, similar to CDS catalyst 30, is fabricated from or otherwise coated with a material that absorbs onto a surface or otherwise internalizes reductant for reaction with NOx (NO and NO2) in the exhaust gas passing therethrough to form water (H2O) and diatomic nitrogen (N2). At the same time, the substrate brick of catalyst 32 may include a region (32B) located generally downstream that is coated with or otherwise contains a different catalyst that oxidizes residual reductant in the exhaust.
A reductant injector 36 may be located at or near an upstream end of tube 24 (e.g., within an upstream end of tube 24, within coupling 26, or within space 34) and configured to inject a reductant into the exhaust flowing through tube 24. A gaseous or liquid reductant, most commonly a water/urea solution, ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, an ammine salt, or a hydrocarbon such as diesel fuel, may be sprayed or otherwise advanced by reductant injector 36 into the exhaust passing through tube 24. Reductant injector 36 may be located a distance upstream of CDS catalyst 30 to allow the injected reductant sufficient time to mix with exhaust and to sufficiently decompose before entering CDS catalyst 30. That is, an even distribution of sufficiently decomposed reductant within the exhaust passing through CDS catalyst 30 may enhance NOX reduction therein. The distance between reductant injector 36 and CDS catalyst 30 (i.e., the length of tube 24) may be based on a flow rate of exhaust passing through aftertreatment module 10 and/or on a cross-sectional area of tube 24. In the example depicted
To enhance incorporation of the reductant with exhaust, a mixer 38 may be located within tube 24. In one embodiment, mixer 38 may include vanes or blades inclined to generate a swirling motion of the exhaust as it flows through tube 24. In another embodiment, mixer 38 may include a ring extending from internal walls of tube 24 radially inward a distance toward a longitudinal axis of tube 24, the ring being configured to promote exhaust flow turbulence within tube 24. In either embodiment, mixer 38 may be located upstream or downstream (shown in
One or more probes may be situated to monitor parameters of aftertreatment module 10. For example, a first probe 40 may be situated within space 34 of second portion 22 (e.g., axially-outward from CDS catalyst 30 relative to a center of canister 12), while a second probe 42 may be situated within second portion 22 at outlet 16 (e.g., axially-between oxidation catalyst 28 and catalysts 30 and 32). In one embodiment, first probe 40 may be a temperature probe configured to generate a first signal indicative of a temperature of the exhaust entering CDS catalyst 30. The first signal may be utilized to determine, among other things, an operating temperature and predicted efficiency of CDS catalyst 30. Second probe 42 may be utilized to detect a constituent of the exhaust exiting catalyst 32, for example a concentration of NOx or residual reductant. Second probe 42 may generate a second signal indicative of this constituent, the second signal being utilized to determine, among other things, an actual effectiveness of CDS catalyst 30 and/or catalyst 32. It is contemplated that first and/or second probes 40, 42 may be configured to monitor other parameters and be utilized for other purposes, if desired.
It is contemplated that access to the treatment devices of aftertreatment module 10 may be helpful in some situations. Thus, in one embodiment, the end-portions of canister 12 enclosing spaces 34 at each opposing end of aftertreatment module 10 may be removably connected to a center portion of canister 12 that encloses oxidation catalyst 28, CDS 30, and catalyst 32. For example, the end-portions could be bolted or latched to the center portion, if desired. With this configuration, the end-portions may be selectively removed for inspection and/or replacement of the various catalysts.
The aftertreatment modules of the present disclosure may be applicable to the exhaust system of any engine configuration requiring constituent conditioning, where component packaging is an important issue. The disclosed aftertreatment modules may improve packaging by utilizing a single canister to house treatment devices, and yet still provide sufficient reductant mixing and decomposition through the use of an external tube. Exhaust flow through aftertreatment module will now be described.
Referring to
After passing through oxidation catalysts 28, the exhaust may flow into space 34 in first portion 20 of canister 12, through tube 24, and into space 34 in second portion 22 of canister 12. At this time, reductant may be injected into the exhaust flow upstream of mixer 38, such that the swirl and/or turbulence of the exhaust promoted by mixer 38 may be utilized to entrain and distribute reductant within the exhaust flow. As the swirling and/or turbulent flow of exhaust and reductant passes along the length of tube 24, the mixture may continue to homogenize and the reductant may begin to decompose. By the time the mixture reaches CDS catalyst 30, the bulk of the reductant should be decomposed for NOx reduction purposes within CDS catalyst 30 and catalyst 32.
As the exhaust passes through CDS catalyst 30, particulate matter may be removed from the exhaust and NOx may react with the reductant to be reduced to water and diatomic nitrogen. The exhaust may then exit CDS catalyst 30 and enter catalyst 32, where additional reduction of NOx may occur and residual reductant may be absorbed. After treatment within catalyst 32, the exhaust may be redirected by wall 18 for discharge to the atmosphere (or other downstream exhaust system components) via outlet 16.
Referring to
As the exhaust passes through CDS catalyst 30′, particulate matter may be removed from the exhaust and NOx may react with the reductant to be reduced to water and diatomic nitrogen. The exhaust may then exit CDS catalyst 30′ and enter catalyst 32′, where additional reduction of NOx may occur and residual reductant may be absorbed. After treatment within catalyst 32′, the exhaust may be redirected for discharge to the atmosphere (or other downstream exhaust system components) via outlet 16′.
Aftertreatment modules 10 and 10′ may promote even exhaust distribution and sufficient reductant decomposition. In particular, the locations of inlets 14, 14′ and outlets 16, 16′, in combination with the inclination of wall 18 may promote even distribution across the treatment devices within canisters 12 and 12′, while the length and location of tubes 24, 24′ together with mixers 38, 38′ may promote reductant decomposition. Spaces 34, 34′, together with the configuration and location of couplings 26, 26′, may also promote distribution and reductant decomposition.
Aftertreatment modules 10 and 10′ may be simple, compact, and relatively inexpensive. Aftertreatment modules 10, 10′ may be simple and compact because they may utilize only a single canister and catalysts that provide multiple functions. For example, CDS catalysts 30, 30′ may provide both particulate trapping and NOx reduction functionality, while catalysts 32, 32′ may provide both NOx reduction and reductant absorbing functionality. The simplicity of aftertreatment modules 10 and 10′ may result in a lower cost solution to exhaust aftertreatment.
It will be apparent to those skilled in the art that various modifications and variations can be made to the aftertreatment module of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the aftertreatment module disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalent.
