Dosing and mixing arrangement for use in exhaust aftertreatment

A method for causing exhaust gas flow to flow at least 270 degrees in a first direction about a perforated tube using a baffle plate having a main body with a plurality of flow-through openings and a plurality of louvers positioned adjacent to the flow-through openings. The method includes deflecting a first portion of the exhaust gas flow with the main body of the baffle plate. The method also includes allowing a second portion of the exhaust gas flow to flow through the flow-through openings of the baffle plate. The method also deflects the second portion of the exhaust gas flow at a downstream side of the main body with the louvers hereby causing the second portion of the exhaust gas flow to flow in the first direction about the perforated tube.

BACKGROUND

Vehicles equipped with internal combustion engines (e.g., diesel engines) typically include exhaust systems that have aftertreatment components such as selective catalytic reduction (SCR) catalyst devices, lean NOx catalyst devices, or lean NOx trap devices to reduce the amount of undesirable gases, such as nitrogen oxides (NOx) in the exhaust. In order for these types of aftertreatment devices to work properly, a doser injects reactants, such as urea, ammonia, or hydrocarbons, into the exhaust gas. As the exhaust gas and reactants flow through the aftertreatment device, the exhaust gas and reactants convert the undesirable gases, such as NOx, into more acceptable gases, such as nitrogen and water. However, the efficiency of the aftertreatment system depends upon how evenly the reactants are mixed with the exhaust gases. Therefore, there is a need for a flow device that provides a uniform mixture of exhaust gases and reactants.

SCR exhaust treatment devices focus on the reduction of nitrogen oxides. In SCR systems, a reductant (e.g., aqueous urea solution) is dosed into the exhaust stream. The reductant reacts with nitrogen oxides while passing through an SCR substrate to reduce the nitrogen oxides to nitrogen and water. When aqueous urea is used as a reductant, the aqueous urea is converted to ammonia which in turn reacts with the nitrogen oxides to covert the nitrogen oxides to nitrogen and water. Dosing, mixing and evaporation of aqueous urea solution can be challenging because the urea and by-products from the reaction of urea to ammonia can form deposits on the surfaces of the aftertreatment devices. Such deposits can accumulate over time and partially block or otherwise disturb effective exhaust flow through the aftertreatment device.

SUMMARY

An aspect of the present disclosure relates to a method for dosing and mixing exhaust gas in exhaust aftertreatment. Another aspect of the present disclosure relates to a dosing and mixing unit for use in exhaust aftertreatment. More specifically, the present disclosure relates to a dosing and mixing unit including a baffle plate configured to direct exhaust gas flow to flow around a perforated mixing tube to effectively mix and dose exhaust gas within a relatively small area.

An aspect of the disclosure includes a method for causing exhaust gas flow to flow at least 270 degrees in a first direction about a perforated tube using a baffle plate. The baffle plate has a main body that defines a plurality of flow-through openings. The baffle plate also includes a plurality of louvers positioned adjacent to the flow-through openings. The main body of the baffle plate has an upstream side and a downstream side. The louvers are positioned at the downstream side of the main body of the baffle plate. The downstream side of the main body of the baffle faces toward the perforated tube. The method includes deflecting a first portion of the exhaust gas flow with the upstream side of the main body of the baffle plate thereby causing the first portion of the exhaust flow to flow around an end of the main body of the baffle plate and around the perforated tube in the first direction. The method also includes allowing a second portion of the exhaust gas flow to flow through the flow-through openings of the baffle plate from the upstream side of the main body to the downstream side of the main body. The method also involves deflecting the second portion of the exhaust gas flow at the downstream side of the main body with the louvers thereby causing the second portion of the exhaust gas flow to flow in the first direction about the perforated tube.

A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based.

DETAILED DESCRIPTION

FIGS. 1-5show a dosing and mixing unit10in accordance with the principles of the present disclosure. The dosing and mixing unit10includes a housing12having a housing body30, an inlet18, and an outlet20. An exhaust treatment substrate50, a perforated tube40, and a baffle52are disposed within the housing12(FIG. 2). Exhaust gas G flows from the inlet18, through the treatment substrate50, through the baffle52, and into the tube40(seeFIG. 4). The baffle52is configured to direct the exhaust gas G to flow in a direction d (seeFIG. 3) about the perforated tube40to enhance swirling within the tube40. The tube40defines the outlet20of the unit10.

As shown inFIG. 3, the housing body30defines a central housing axis32between a first end34and a second opposite end36. A length L of the main housing body30extends along the central housing axis32between the first and the second ends34,36of the main housing body30(FIG. 3). The inlet18is adjacent the first end34of the main housing body30and the outlet20is adjacent the second end36of the main housing body30. The exhaust treatment substrate50is positioned within the main housing body30between the inlet18and the perforated tube40. The main housing body30defines an interior volume V (seeFIG. 3) that extends between an exhaust treatment substrate50and the perforated tube40. The interior volume V defines a transverse cross-sectional area A that is transverse relative to the central housing axis32(seeFIG. 9).

The perforated tube40is disposed towards the second end of the main housing body30. In certain embodiments, the second end36of the main housing body30includes a curved portion46that curves partially around the perforated tube40. As used herein, a “perforated tube” is a conduit having a plurality of side holes. The use of the term “perforated” is not dependent on the method(s) used to make the side holes (i.e., the holes can be made in any way and need not be formed by a stamping/perforation type process). The perforated tube40defines a tube axis42aligned at an angle0relative to the central housing axis32(seeFIG. 5).

The baffle plate52is positioned within the interior volume V between the perforated tube40and the exhaust treatment substrate50. In certain embodiments, the baffle plate52is separate from and not connected to the perforated tube40. As shown inFIGS. 6-8, the baffle plate52includes a main plate body54having an upstream side56that faces toward the exhaust treatment substrate50and a downstream side58that faces toward the perforated tube40(also seeFIG. 3). In certain embodiments, the main body54of the baffle plate52extends only partially around the perforated tube40. In certain embodiments, the main body54of the baffle plate52extends along less than fifty percent of a circumference of the perforated tube40. In certain embodiments, the main body54of the baffle plate52extends along less than one-third of a circumference of the perforated tube40. In certain embodiments, the main body54of the baffle plate52extends along less than one-quarter of a circumference of the perforated tube40.

In certain embodiments, the main body54of the baffle plate52has a curvature defined by an arc having a radius centered on a centerline of the perforated tube40. In some embodiments, the upstream side56of the main body54has a convex curvature and the downstream side58of the main body54has a concave curvature (seeFIG. 8). In some of these embodiments, the convex and concave curvatures curve partially around the perforated tube40(seeFIG. 3).

The main plate body54defines a plurality of flow-through openings60that extend through the main plate body54between the upstream and downstream sides56,58of the main plate body54. The openings60enable treated exhaust gas G to flow through the baffle52towards the tube40(seeFIGS. 4 and 5). In certain embodiments, the perforated tube40defines circular openings45and the baffle plate52defines rectangular openings60. In certain embodiments, the openings45of the perforated tube40are smaller in area than the openings60in the baffle plate52.

In accordance with some aspects of the disclosure, the baffle plate52also includes one or more louvers62positioned adjacent to the flow-through openings60of the main plate body54. In some implementations, the louvers62are disposed at the downstream side58of the plate body54. In other implementations, one or more louvers62can be positioned at the upstream side56or at both the upstream and downstream sides56,58of the plate body54. In certain embodiments, the louvers62have base ends63that are integral/unitary with the main body54of the baffle plate52. Free ends65of the louvers62extend laterally away from the main plate body54. The louvers62direct the gas G passing through the openings60in a flow direction d (FIG. 3) around the tube40. The flow direction d generated by the louvers62encourages the swirling exhaust gas G to remain within the perforated tube40once the exhaust gas G has entered the perforated tube40. Treated gas G also flows beneath the free edge66of the baffle52towards the curved portion46of the housing body30, which further directs the gas G around the tube40in the flow direction d (seeFIGS. 4 and 5).

In certain embodiments, an exhaust flow path extends 360 degrees about the circumference of the perforated tube40, and the baffle plate52coincides with only a portion the flow path. In certain embodiments an exhaust flow path extends 360 degrees about the circumference of the perforated tube40, and the baffle plate52coincides with less than one-third or less than one-quarter of the flow path. In certain embodiments, the main body54of the baffle plate52curves around only a portion of the circumference of the perforated tube40. In certain embodiments, an exhaust flow path extends 360 degrees about the circumference of the perforated tube40, the exhaust flow travels in a single rotational direction about the perforated tube40along the exhaust flow path, the baffle plate52coincides with only a first portion the exhaust flow path, and the louvers62encourage the flow in the single rotational direction within the first portion of the exhaust flow path and assist in preventing exhaust from exiting the perforated tube40along the first portion of the exhaust flow path. In certain embodiments, an exhaust flow path extends 360 degrees about the circumference of the perforated tube40, the exhaust flow travels in a single rotational direction about the perforated tube40along the exhaust flow path, the baffle plate52coincides with only a first portion the exhaust flow path, the louvers62of the baffle plate52function as first swirl structures that encourage the flow in the single rotational direction within the first portion of the exhaust flow path, and a curved portion46of an outer housing30that curves along a portion of the perforated tube40and coincides with a second portion of the exhaust flow path functions as a second swirl structure that encourages the flow in the single rotational direction within the second portion of the exhaust flow path.

As shown inFIGS. 4 and 5, a first portion80of the exhaust gas G flowing through the housing12is directed though the open flow area A1and then in the first rotational direction d around the perforated tube40(seeFIGS. 4 and 5). The dosing and mixing unit10also is configured such that also a second portion82of the exhaust gas flow passes through the flow-through openings60and is deflected in the first rotation direction d about the perforated tube40by the louvers62. In some implementations, the second portion82proceeds at least 180° in the first rotational direction d around the tube40before entering the tube40through the perforations. In certain implementations, the second portion82proceeds at least 270° in the first rotational direction d around the tube40before entering the tube40through the perforations. In one example embodiment, second portion82proceeds at least 360° in the first rotational direction d about the perforated tube40before entering the tube40through the perforations.

The main plate body54has a connected edge64that is connected to an interior of the main housing body30. In some implementations, the main plate body54has a free edge66that extends across the interior volume V of the main housing body30. In such implementations, the main plate body54is sized and shaped to coincide with only a portion of the transverse cross-sectional area A of the interior volume V such that an open flow area A1(seeFIG. 9) is defined between the free edge66and the interior of the main housing body30. In some embodiments, the free edge66is generally parallel to the tube axis42(seeFIG. 9). In other embodiments, the free edge66and the tube axis42can be angled relative to one another.

In some implementations, a portion of the perforated tube40extends below the free edge66of the baffle plate52and overlaps the open flow area A1(seeFIG. 9). In some implementations, between about 10% of the perforated tube40and about 50% of the perforated tube40overlaps the open flow area A1. In certain implementations, less than 40% of the perforated tube40overlaps the open flow area A1. In certain implementations, less than 33% of the perforated tube40overlaps the open flow area A1. In certain implementations, no less than 20% of the perforated tube40overlaps the open flow area A1. In certain implementations, no less than 25% of the perforated tube40overlaps the open flow area A1.

In other implementations, the main plate body54of the baffle52extends fully across the interior volume V of the main housing body30. In such implementations, the main plate body54defines an aperture separate from the flow-through openings60. The aperture extends over a significant portion of the surface area of the main plate body54to expose at least the portion of the cross-sectional area A located beneath the tube40. In certain implementations, the aperture also may extend across a portion of the tube40. For example, in some implementations, the aperture extends over about 10% to about 60% of the main plate body54. In certain implementations, the aperture extends over about 20% to about 50% of the main plate body54. In certain implementations, the aperture extends over no less than 30% and no more than 55% of the main plate body54.

In still other implementations, first and second apertures can be defined in the main plate body54separate from the flow-through openings60. The first aperture aligns with a portion of the perforated tube40. The second aperture defines the open flow area (similar to open flow area A1ofFIG. 9). In certain implementations, the second aperture does not overlap with the perforated tube40. In certain implementations, the first aperture extends over no more than 20% of the main plate body54and the second aperture extends over no more than 30% of the main plate body54.

In some implementations, the dosing and mixing unit10also can include a reactant dispenser84for dispensing reactant86within an interior of the perforated tube40such that the reactant86is mixed with the exhaust gas flow within the interior of the perforated tube40(seeFIG. 5). Examples of the reactant include, but are not limited to, ammonia, urea, or a hydrocarbon. In other embodiments, the reactant dispenser84may be positioned upstream from the perforated tube40or downstream from the perforated tube40. The dispenser84can be aligned with the center axis42of the perforated tube40so as to generate a spray pattern concentric about the axis42.

In some embodiments, a treatment substrate99is positioned downstream from the perforated tube40(seeFIG. 5). Example treatment substrates99suitable for use with the tube40include, but are not limited to, a lean NOx catalyst substrate, a SCR substrate, a SCRF substrate (i.e., a SCR coating on a particulate filter), and a NOx trap substrate. In some embodiments, the treatment substrate is an SCR substrate for treating NOx and the reactant is selected from the group consisting of ammonia and urea.

A selective catalytic reduction (SCR) catalyst device is typically used in an exhaust system to remove undesirable gases such as nitrogen oxides (NOx) from the vehicle's emissions. SCR's are capable of converting NOx to nitrogen and oxygen in an oxygen rich environment with the assistance of reactants such as urea or ammonia, which are injected into the exhaust stream upstream of the SCR through the doser84. In alternative embodiments, other aftertreatment devices such as lean NOx catalyst devices or lean NOx traps could be used in place of the SCR catalyst device, and other reactants (e.g., hydrocarbons) can be dispensed by the doser.

A lean NOx catalyst device is also capable of converting NOx to nitrogen and oxygen. In contrast to SCR's, lean NOx catalysts use hydrocarbons as reducing agents/reactants for conversion of NOx to nitrogen and oxygen. The hydrocarbon is injected into the exhaust stream upstream of the lean NOx catalyst. At the lean NOx catalyst, the NOx reacts with the injected hydrocarbons with the assistance of a catalyst to reduce the NOx to nitrogen and oxygen. While the exhaust treatment systems400and500will be described as including an SCR, it will be understood that the scope of the present disclosure is not limited to an SCR as there are various catalyst devices that can be used in accordance with the principles of the present disclosure.

The lean NOx traps use a material such as barium oxide to absorb NOx during lean burn operating conditions. During fuel rich operations, the NOx is desorbed and converted to nitrogen and oxygen by reaction with hydrocarbons in the presence of catalysts (precious metals) within the traps.

In other implementations, the dosing and mixing unit10can be used to mix hydrocarbons with the exhaust to reactivate a diesel particulate filter (DPF). In such implementations, the reactant dispenser84injects hydrocarbons into the gas flow within the perforated tube40. The mixed gas leaves the tube40and is directed to a downstream diesel oxidation catalyst (DOC) at which the hydrocarbons ignite to heat the exhaust gas. The heated gas is then directed to the DPF to burn particulate clogging the filter.

As shown inFIGS. 10 and 11, some examples of the dosing and mixing unit10also can include a perforated plate105positioned within the main housing body30of the dosing and mixing unit10. In some embodiments, the perforated plate105is positioned between the inlet18and the exhaust treatment substrate50. In some examples, the perforated plate105includes a flat plate body107having a plurality of apertures109to distribute the exhaust gas G within the main housing body30before the gas reaches the exhaust treatment substrate50(FIG. 12). In other examples, other types of flow distribution devices can be utilized. In still other examples, no devices are positioned between the inlet18and the exhaust treatment substrate50.

In use of the dosing and mixing unit10, exhaust enters the housing12of the dosing and mixing unit10through the inlet18into the main housing body30. From the inlet18, the exhaust flow G moves through the perforated plate105(if utilized), through the substrate50, and into the interior volume V of the housing body30(seeFIG. 4). At the interior volume V, the first portion80of the exhaust gas G flows past the free edge66of the main body54of the baffle plate52and through the open area A1. Upon passing through the open area A1, the first portion80of the exhaust flow G is directed toward the curved portion46of the housing12, which encourages the first portion80of the exhaust flow to flow in the first rotational direction d around a first side41(seeFIG. 3) of the perforated tube40. In certain implementations, some of the gas flow G can initially deflect off the upstream side56of the main body54of the baffle plate52towards the free edge66.

The second portion82of the exhaust gas flow G flows through the flow-through openings60of the baffle plate52from the upstream side56of the main body54to the downstream side58of the main body56. The second portion82of the exhaust gas flow G is deflected at the downstream side58of the main body54with the louvers62. This deflection causes the second portion82of the exhaust gas flow G to flow in the first rotational direction d around a second side43(seeFIG. 3) of the perforated tube40. The first and second sides41,43are opposite sides of the perforated tube40. As shown inFIG. 4, the exhaust gas (the combination of the first and second portions80,82) flows at least 270 degrees (preferably about 360 degrees) in the first direction d about the perforated tube40.

The exhaust gas G swirling about the perforated tube40in the first rotational direction d enters the openings in the perforated tube40and continues to swirl in the first rotational direction d within the perforated tube40. The reactant dispenser84(seeFIG. 5) dispenses reactant86into the swirling exhaust flow within the perforated tube40. The swirling of the exhaust gas causes the reactant86to be mixed with the exhaust gas within the perforated tube40. The exhaust flow then exits the housing12through the outlet18defined by the perforated tube40and proceeds to the downstream exhaust treatment substrate99(seeFIG. 5). Mixing can continue as the exhaust gas flows from the perorated tube40to the substrate99.