Patent Description:
<CIT> discloses a device for introducing a fluid into a gas stream, in which an elbow is formed into an exhaust pipe. Urea liquid is injected via the elbow in the direction of the exhaust pipe through a first intermediate cone structure. The output of the intermediate cone is directed to a second intermediate cone arrangement or protective sleeve. Exhaust gas is directed into both intermediate cone structures. A partitioning is formed such that some of the exhaust gas is directed to a stem part of the first intermediate cone structure. Remainder of the exhaust gas further divided through the second intermediate cone structure and through a gap between the second intermediate cone structure and the exhaust pipe. Swirl structures are also disclosed between the protective sleeve and the exhaust pipe as well as at a gap surrounding a metering tip.

Exhaust gas after-treatment has limited room both in terms of physical space allowed and in terms of counter pressure that may be formed. <CIT> requires a length of the exhaust pipe that is roughly <NUM> times the diameter of the exhaust pipe at the protective sleeve. Moreover, the more turbulence is formed, the better the reactant generally evaporates, but the higher the pressure drop is required. <CIT> induces plenty of turbulence and pressure loss on entry of exhaust gas into first intermediate cone in particular, and the gap between the protective sleeve and the exhaust pipe is long and shallow. Sheer number of materials in the mixer of <CIT> further adds weight and heating time required before the mixer can efficiently start evaporating liquid urea. Increased counter pressure of exhaust gas may also adversely inhibit emptying of engine cylinders of exhaust gas.

<CIT> discloses a device for introducing a fluid into a gas stream. <CIT> discloses an exhaust system with mixer. <CIT> discloses an exhaust aftertreatment system having mixer assembly. <CIT> discloses a dual-swirl inclined cylindrical type urea mixer and application in exhaust after-treatment device thereof. <CIT> discloses a whirl blade and integrated mixing arrangement of clam shell.

An object of the invention is to allow reducing counter pressure of exhaust gas mixing with reactant with compact structures. Another object of the invention is to provide a new technical alternative to existing techniques and/or to address any of the known problems of the prior art.

According to a first example aspect there is provided a flow device for exhaust gas aftertreatment as defined by appended claim <NUM>.

The flow device may be a mixer for mixing reactant with exhaust gas.

Advantageously, by mixing tube being obliquely supported to and extending through the peripheral wall of the mixing chamber, the reactant doser mount can be made suitable for air-free reactant dosers that deliver the reactant without a gaseous carrier. Reactant dosers with pneumatic carrier are notoriously well suited for dosing at any desired point into the exhaust flow, whereas air-free reactant dosers require significantly more space at reactant output. It is particularly advantageous to use an air-free doser in application where pressurised air is not otherwise required for pneumatic breaks, for instance. Tractors, forest machines, and various other machines may particularly benefit of the flow device of the first example aspect, especially though not exclusively where power transfer is performed solely by mechanical, hydraulic, and electric transmission.

The mixing tube may comprise a first end that extends through the peripheral wall of the mixing chamber. The first end may be closed. The closing of the first end may refer to blocking entry and exit of exhaust gas, while reactant may still be dosed through the first end with a doser.

The exhaust gas may be allowed to freely flow along a portion of an outer surface of the mixing tube that resides inside the mixing chamber.

The mixing tube may comprise a vestibule defined by the closed first end and a flange spaced apart of the first end. The mixing tube may comprise a first cylindrical or conical guide attached to the first end. The mixing tube may comprise a second cylindrical or conical guide attached to the flange. The first cylindrical or conical guide may be laterally aligned with the second cylindrical or conical guide. The first cylindrical or conical guide may be spaced apart of the second cylindrical or conical guide such that a gap is formed therebetween. The first cylindrical or conical guide may comprise peripheral apertures for receiving exhaust gas from the vestibule. The second cylindrical or conical guide may be peripherally closed. The gap and the peripheral exhaust gas entry of the mixing tube may be aligned in the flow direction of the reactant.

Advantageously, the flange may direct some of the exhaust gas entering through the peripheral exhaust gas entry to form an escort flow for the output of the reactant doser. The first cylindrical or conical guide may facilitate the forming or guiding of the escort flow. The second cylindrical or conical guide may facilitate the forming or guiding of the escort flow. The second cylindrical or conical guide may facilitate the forming or guiding of the escort flow by partly obstructing flow out of the vestibule onwards along the mixing tube.

Advantageously, the method may provide a convenient escort flow that is relatively insensitive to prevailing flow rate of the exhaust gas.

The mixing tube may comprise one or more peripheral apertures downstream from the peripheral exhaust gas entry of the mixing tube. The mixing tube may comprise one or more peripheral apertures downstream from the flange.

The mixing tube may have an angle or turn dividing the mixing tube into an entry section and an exit section. The exit section may be parallel with a longitudinal axis of the mixing chamber or at least within <NUM> degrees from the parallel with the longitudinal axis of the mixing chamber. A centreline length of the exit section may be at most <NUM> % or <NUM> % of that of the entry section. The centreline length may be measured along the centreline of the entry or exit section.

The entry section may have a circular cross-section. The entry section may be cylindrical. The entry section may be conical.

The exit section may have a circular cross-section. The exit section may be cylindrical. The exit section may be conical.

The swirl arrangement may be configured to at least locally bridge a gap between an inner wall of the mixing chamber and an outer wall of the mixing tube. The bridging of the gap may refer to closing at least <NUM> % of the distance between the inner wall of the mixing chamber and the outer wall of the mixing tube.

The swirl arrangement may comprise two or more guides extending along at least <NUM> degrees around the inner wall of the mixing chamber. The two or more guides may extend by at least <NUM>; <NUM>; <NUM>; or <NUM> % in a longitudinal direction of the mixing chamber downstream to a leading edge of the peripheral exhaust gas entry.

The mixing tube may have a round cross-section. The mixing tube may have a circular cross-section. The mixing tube may have an elliptic cross-section.

The mixing chamber may have a round cross-section. The mixing chamber may have a circular cross-section. The mixing chamber may have an elliptic cross-section.

The mixing chamber may have a mixing chamber input and a mixing chamber output at opposite ends of the mixing chamber. The mixing chamber may have a longitudinal axis extending through the mixing chamber input and the mixing chamber output. The mixing chamber may have a longitudinal axis coaxially with the mixing chamber input and the output of the mixing chamber. The exit section may be coaxial with the longitudinal axis of the mixing chamber.

The exhaust gas may be configured to flow through the mixing tube free of rotation, while the exhaust gas flowing around the mixing tube is rotated at least at an exit of the mixing tube. Advantageously, shear forces may be induced into any remaining drops or droplets of reactant arriving from the mixing tube to a rotating edge flow about the end of the mixing tube. The shear forces may help evaporation of liquid reactant and/or accelerate reactions such as hydrolysis and / or thermolysis of the reactant.

The reactant doser mount may be configured to enable mounting the reactant doser in at least two different angles with relation to the longitudinal axis.

According to a second example embodiment there is provided a system comprising the flow device of the first example aspect.

The system may further comprise a turbocharger connector for receiving exhaust gas from a turbocharger and transferring the exhaust gas to the flow device so that the exhaust gas arrives to the mixing chamber with a residual swirl from the turbocharger. The swirl arrangement may be configured to enforce the residual swirl.

The system may comprise a pre-rotation arrangement configured to induce a swirl in the exhaust gas arriving in the mixing chamber. The pre-rotation arrangement may comprise a turbocharger. Additionally, or alternatively, the pre-rotation arrangement may comprise one or more dedicated, optionally static, swirl elements.

The system may comprise a diesel oxidation catalyst, DOC. The system may comprise a diesel particulate filter, DPF. The system may comprise a selective catalytic reduction, SCR, catalyst.

The system may comprise an intermediate connector pipe between an exit of the mixing chamber and subsequent catalytic or filtration treatment.

The intermediate connector pipe may be insulated to reduce heat loss. The mixing chamber may be insulated.

The system may comprise two reactant mixing device. One or more of the reactant mixing devices may be the flow device of the first example aspect. In downstream direction, a latter reactant mixing device may comprise a pre-swirl arrangement configured to form a swirl in the exhaust gas upstream from the mixing tube.

The latter reactant mixing device may comprise one or more blades partly surrounding a mixing pipe of the latter reactant mixing device and forming a rotating and circulating flow about the mixing pipe. The latter mixing device may guide exhaust gas into the mixing pipe through peripheral apertures and / or an end gap of the mixing pipe. The latter mixing device may be configured to form a rotating and advancing gas flow along the mixing pipe both inside and outside the mixing pipe.

The latter reactant mixing device may be a Proventia SuperTornado™. The latter reactant mixing device may be an apparatus for aftertreatment of exhaust gas comprising an inline housing as disclosed in <CIT>.

According to a third example aspect there is provided a method of guiding a flow of exhaust gas for aftertreatment as defined by appended claim <NUM>.

The method may further comprise allowing the exhaust gas to freely flow along a portion of an outer surface of the mixing tube that resides inside the mixing chamber.

The method may further comprise defining in the mixing tube a vestibule by a closed first end of the mixing tube and a flange in the mixing tube, which flange is spaced apart of the first end. The method may further comprise guiding exhaust gas and reactant flows in the vestibule by an entry guide structure in the vestibule, around and extending from the reactant doser mount deeper into the mixing tube.

The method may further comprise guiding the exhaust gas to flow through the mixing tube without a rotation, while guiding the exhaust gas flowing around the mixing tube to rotate at least at an exit of the mixing tube.

The method may further comprise receiving by a turbocharger connector the exhaust gas from a turbocharger to the mixing chamber with some residual swirl from the turbocharger. The swirl arrangement may be configured to enforce the residual swirl.

The method may further comprise inducing a swirl in the exhaust gas arriving in the mixing chamber by a pre-rotation arrangement.

The method may further comprise conducting the exhaust gas to the flow device or from the flow device to subsequent catalytic or filtration treatment by an intermediate connector pipe. The method may further comprise insulating the intermediate connector pipe to reduce heat loss. The method may further comprise insulating the mixing chamber. The intermediate connector pipe may be at least <NUM> long. The intermediate connector pipe may be at least <NUM> long. The intermediate connector pipe may be at least <NUM> long. The intermediate connector pipe may be at least <NUM> long. The intermediate connector pipe may at most <NUM> long. The intermediate connector pipe may at most <NUM> long. The intermediate connector pipe may at most <NUM> long.

The method may further comprise performing after-treatment by at least two reactant mixing devices.

<FIG> shows an exhaust gas after-treatment system of an example embodiment, comprising a first mixer <NUM>; an intermediate connector pipe <NUM>; a first selective catalytic reduction, SCR, catalyst <NUM>; a diesel oxidation catalyst, DOC <NUM>; a diesel particulate filter, DPF <NUM>; a second mixer <NUM>; a second SCR <NUM>; an output pipe <NUM>; and a sampling port <NUM>.

<FIG> shows a cross-section of the system of <FIG>. In this embodiment, the second mixer <NUM> has one or more blades partly surrounding a mixing pipe of the latter reactant mixing device and forming a rotating and circulating flow about the mixing pipe. In an example embodiment, the second mixer <NUM> is configured to guide exhaust gas into the mixing pipe through peripheral apertures and / or an end gap of the mixing pipe. In an example embodiment, the second mixer <NUM> is configured to form a rotating and advancing gas flow along the mixing pipe both inside and outside the mixing pipe.

<FIG> show detailed views of the mixer <NUM> of <FIG>.

<FIG> shows a section view of the mixer <NUM> of <FIG> (sectioned along line A-A of <FIG>). <FIG> illustrates a mixing chamber <NUM> that comprises a mixing chamber input <NUM>; swirl flow guides <NUM>; and a mixing chamber output <NUM>. The mixer <NUM> further comprises a mixing tube <NUM> and a doser <NUM>. The mixing tube <NUM> comprises an entry section <NUM>; an exit section <NUM>; and a mixing tube output <NUM>. The swirl flow guides <NUM> contribute to forming, collectively with other parts such as inner walls of the mixing chamber and external walls of the mixing tube <NUM>, a swirl arrangement. The swirl arrangement produces a swirl about at least the mixing tube output <NUM>.

The exhaust gas entry comprises one or more apertures <NUM> in the mixing tube, on a side facing towards incoming exhaust gas and residing peripherally in a sector of at most <NUM> degrees about a longitudinal axis of the mixing tube at the exhaust gas entry.

<FIG> shows a section view of the mixer <NUM> of <FIG> without a doser. <FIG> further illustrates a reactant doser mount <NUM> for mounting the doser <NUM>. The mixing tube <NUM> has a first end <NUM> that closes the mixing tube <NUM> around the doser mount <NUM>. Inside the mixing tube <NUM>, there is a cylindrical or conical guide <NUM> connected to the first end <NUM>. A flange <NUM> positioned in the entry section defines a vestibule <NUM>. A second cylindrical or conical guide <NUM> is attached to the flange, for directing exhaust gas from the vestibule <NUM> forward along the first section <NUM> of the mixing tube <NUM>. In <FIG>, the first cylindrical or conical guide is laterally aligned with the second cylindrical or conical guide <NUM>. The first cylindrical or conical guide <NUM> is drawn spaced apart of the second cylindrical or conical guide <NUM> such that a gap is formed therebetween. While in another example embodiment the first cylindrical or conical guide is closed, the one in <FIG> has peripheral apertures <NUM> for receiving exhaust gas from the vestibule. Likewise, or alternatively, the second cylindrical or conical guide <NUM> may be peripherally closed as in <FIG>. Alternatively, there may be some apertures in the second cylindrical or conical guide <NUM>.

Further down the first section and / or in the second section, there may be further apertures. <FIG> shows a plurality of peripheral apertures <NUM> downstream after the vestibule <NUM> and a further aperture <NUM>. An entry opening with integral guide may also be formed as shown with reference sign <NUM>. The integral guide may guide exhaust gas into the mixing tube and / or contribute into forming a swirl about the mixing tube output <NUM>.

<FIG> show a mixer of an alternative example embodiment. In this embodiment, the doser <NUM> is mounted at a different angle. This is implemented by a different reactant doser mount <NUM>' that is not obliquely connected to the first end of the mixing tube. Additionally, here the doser mount <NUM>' is directly connected to the first end without a mounting pipe part.

<FIG> shows an exhaust gas after-treatment system <NUM>' of an alternative example embodiment. This embodiment differs from that of <FIG> in that there is a pre-swirl arrangement <NUM> configured to form a swirly upstream from the mixer <NUM>. The system of <FIG> is convenient, for example, when mounted downstream a turbocharger such that residual swirl resides in the exhaust gas entering the mixing chamber of the mixer <NUM>.

<FIG> schematically shows a portion of system of <FIG> with a turbocharger <NUM>. Here, the system has a turbocharger connector, such as the mixing chamber input <NUM>, for receiving exhaust gas from the turbocharger <NUM> and for transferring the received exhaust gas to the mixer <NUM> so that the exhaust gas arrives to the mixing chamber with a residual swirl from the turbocharger.

<FIG> shows a flow chart of an exhaust gas after-treatment process of an example embodiment. <FIG> illustrates a method of guiding a flow of exhaust gas for aftertreatment comprising various possible steps including some optional steps while also further steps can be included and/or some of the steps can be performed more than once:.

Various embodiments have been presented. It should be appreciated that in this document, words comprise; include; and contain are each used as open-ended expressions with no intended exclusivity.

Claim 1:
A flow device (<NUM>) for exhaust gas aftertreatment, comprising
a mixing chamber (<NUM>);
a mixing tube (<NUM>) that resides mostly in the mixing chamber (<NUM>) and is obliquely supported to and extending through a peripheral wall of the mixing chamber (<NUM>);
a reactant doser mount (<NUM>) for a reactant doser (<NUM>) to dose reactant to the mixing tube (<NUM>); characterised in that
the mixing tube (<NUM>) has a peripheral exhaust gas entry (<NUM>) configured to receive exhaust gas at reactant stream arriving from the doser (<NUM>), and a mixing tube output (<NUM>);
the peripheral exhaust gas entry comprises one or more apertures (<NUM>) in the mixing tube on a side facing towards incoming exhaust gas, the one or more apertures residing peripherally in a sector of at most <NUM> degrees about a longitudinal axis of the mixing tube; and
the flow device (<NUM>) has a swirl arrangement around the mixing tube (<NUM>), configured to form a rotating flow around the mixing tube output (<NUM>) and to enhance exhaust gas flow through the mixing tube (<NUM>) by forming some pressure around the mixing tube (<NUM>) downstream from the peripheral exhaust gas entry (<NUM>).