GB2514567A

GB2514567A - Aftertreatment system having a combined wall-flow and flow-through substrate

Info

Publication number: GB2514567A
Application number: GB1309536.9A
Authority: GB
Inventors: Michael A Potter; David B Brown
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2013-05-28
Filing date: 2013-05-28
Publication date: 2014-12-03
Also published as: GB201309536D0

Abstract

An exhaust aftertreatment system for a vehicle having an internal combustion engine. The aftertreatment system comprises a single substrate 600 with a plurality of exhaust gas channels. Some channels are open at both ends, and other channels have a porous surface and are plugged at one end. The substrate comprises an outer cone 650 having channels open at both ends, and an inner cone 670 having channels with a porous surfaces and plugged at one end. Exhaust gases are redirected from the outer cone to the inner cone. The outer cone may accommodate a flow-through diesel oxidation catalyst, and the inner cone may accommodate a wall-flow diesel particulate filter. The outer cone may also accommodate a flow-through ammonia clean up catalyst. The inner cone may also accommodate a selective catalytic reduction system.

Description

AFTER TREA TMENT SYSTEM HA V!NG A COMBINED

WALL-FLOW AND FLOW-THROUGH SUBSTRATE

TECHNICAL FIELD

The present disclosure relates to an after treatment system for purifying exhaust gases of an automotive vehicle having an internal combustion engine, the aftertreatment system comprising a combined wall-flow and flow-through substrate.

BACKGROUND

It is known that modern engines are provided with one or more exhaust aftertreatment systems, also called catalytic converters. In general, a catalytic converter consists of a catalyst substrate or core, which is usually a ceramic monolith with a honeycomb structure, carrying the catalytic layer or coating. The aftertreatment systems may be any device configured to change the composition of the exhaust gases. Example of them are a diesel oxidation catalyst (DOC) located in the exhaust line for degrading residual hydrocarbons (HC) and carbon oxides (CO) contained in the exhaust gas; a Lean NO Trap (LNT)I which is provided for trapping nitrogen oxides NO contained in the exhaust ás7and is located in the exhaust line.

Further examples are exhaust gas aftertreatment systems for the emissions reduction and in particular of particulates and oxides of nitrogen (NOr) from the diesel engine exhaust gas. These systems are provided with aftertreatment devices installed along the exhaust line of the engine and typically comprise a diesel particulate filter (DPF) for control of particulates, and selective catalytic reduction (5CR) system for NOx control.

As can be easily imagined, this plurality of aftertreatment devices implies severe packaging and cost issues, which influence the application of a range of engine aftertreatrrient technologies. As a result, there is a general trend to look for ways to merge aftertreatment components and functions into a lower number of devices.

Currently, aftertreatment systems which commonly need both flow-through devices (DQC1 LNT, SCR, etc) as well as wall-flow, filter (DPF), always need to provided individual components for each of these two types of flow paths. This has a negative impact on system cost and may prevent some packaging solutions since vehicle integration can be difficult. Thi traditional arrangement also drives significant system mass and surface area, which inhibits system warm up and cycle conversion efficiency.

Some attempts have been done in reducing the number of aftertreatment devices. The two-way selective catalytic reduction system comprising a diesel particulate filter (SCR/DPF or SCRE) is one example of a technology that is being applied in this view: in the same component, the selective catalytic reduction system and the particulate filter are merged. . -Further attempts can be found, for example, as disclosed in the patent application DE112007002155A: an exhaust treatment packaging apparatus includes an elongate exhaust gas passage comprising an inlet for the entrance of flowing exhaust gases and an outlet for the exit of the gases, A catalytic device comprising an inlet and an outlet completely or partially overlaps the passage to reduce the length required for the system.

The passage outlet is disposed adjacent the catalytic device inlet, and a flow connector connects the passage outlet to the catalytic device inlet. A particulate filter or other treatment device may be substituted for or added to the catalytic device.

Another example is disclosed in the patent application DE10155086A, where an automotive exhaust gas system has an outer mantle around a cylindrical catalytic body containing an inner cylindrical filter core. The mantle has an exhaust gas inlet and an outlet. Incoming gas passes first through the catalytic body before reversing direction via deflection baffles to pass through the filter core to the outlet. The cylindrical catalyst is separated from the inner filter core by a temperature compensation layer. The catalytic section and filter section have the same length and are constructed in one piece by welding or soldering.

Indeed, these known ideas realize a good packaging solution just assembling different bricks, normally ceramic bricks one inside the other. Unfortunately, the sealing between each other is very difficult: the inner brick will result in compression, while the outer brick in traction and the temperature compensation layer, normally made of steel, cannot ensure a proper sealing. Moreover, as known, ceramic materials have a tensile strength which is one order of magnitude lower than the compression strength. Therefore, from a structural point of view, the ceramic brick which is in traction cannot assure a proper mechanical resistance.

Document US 2003/0190269A1 describes an exhaust aftertreatment combined filter and catalytic converter comprising a plurality of flow channels each having both: a) a flow-through channel catalytically reacting with said exhaust; and b) a wall-flow channel trapping particulate. This disclosure, even if describes a combined filter and catalytic converter, made of a single substrate, does not teach how to solve all issues related to the multiple functions an aftertreatment system should deal with.

Therefore a need exists for a new layout of the aftertreatment system which can be advantageous in terms of packaging and cost, without showing mechanical drawbacks in terms of resistance and sealing and being very flexible in accomplishing all requirements of a modern aftertreatment system.

An object of this invention is to provide an aftertreatment system comprising a substrate suitable to perform all functions required by a whatever complex aftertreatment system.

These objects are achieved by an aftertreatment system and by an internal combustion engine.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An embodiment of the disclosure provides an aftertreatment system for purifying exhaust gases of an automotive vehicle having an internal combustion engine, the aftertreatment system comprising a single substrate with a plurality of exhaust gas channels, wherein some exhaust channels are open at both ends and other channels have a porous surfaces and are plugged at one end, characterized in that the substrate comprises an outer cone, configured to accommodate exhaust channels open at both ends, an inner cone, configured to accommodate exhaust channels having a porous surface and plugged at one end, and a portion through which the exhaust gases are redirected from the outer cone to the inner cone.

An advantage of this embodiment is that a single substrate can provide all the different functions which are required by an aftertreatment system (e.g. catalytic oxidations, filtering, cleaning): in fact, its outer cone accommodates exhaust channels open at both ends, that is to say, channels where exhaust gases can flow through and the catalytic reactions (oxidations, reductions) can take place, while its inner cone accommodates exhaust channels having a porous surface and plugged at one end, that is to say.

channels where filtering processes can take place. Moreover, a suitable layout to redirect exhaust gases from the outer cone (flow-through part of the substrate) to the inner cone is also provided inside the single substrate.

According to another embodiment of the invention, said outer cone accommodates a flow-through diesel oxidation catalyst and said inner cone accommodates a wall-flow diesel particulate filter.

The most used aftertreatment system, at least for engine applications according to the Euro 4 emission standard (and inferiors) is the sequence diesel oxidation catalyst plus diesel particulate filter. Thanks to this embodiment, this layout is provided by a single substrate.

According to an aspect of this embodiment, said outer cone comprises an inlet pipe, through which the exhaust gases enter the substrate and said inner cone comprises an outlet pipe, through which the exhaust gases exit the substrate.

An advantage of this aspect is that the substrate internal layout allows the exhaust gases to be directed in the different portions of the combined substrate and cannings and cones can be arranged to direct the flow as necessary.

According to a further aspect, both inlet pipe and outlet pipe of the substrate are coaxial with the substrate itself.

An advantage of this aspect is that the substrate layout allows alternative arrangements which can also facilitate a more conventional In One End and Out the Other" arrangement.

According to a further embodiment, said outer cone accommodates a flow-through diesel oxidation catalyst and said inner cane accommodates a wall-flow selective catalytic reduction system comprising a diesel particulate filter.

As mentioned, the two-way selective catalytic reduction system comprising a diesel particulate filter is a component where the selective catalytic reduction system and the particulate filter are merged. An advantage of this embpdiment is that it allows to implement more complex aftertreatment functions (DOC + SCRF) always in a single substrate.

According to an aspect of this embodiment, said outer cone comprises an inlet pipe, through which the exhaust gases enter the substrate, said inner cone comprises an outlet pipe, through which the exhaust gases exit the substrate, being both inlet pipe and outlet pipe coaxial with the substrate, and said portion, through which the exhaust gases are redirected from the outer cone to the inner cone, is provided with an urea injector and a mixing device, -According to this embodiment, in the substrate portion, redirecting the gases from the outer cone to the inner cone, other components can be added to implement more complex aftertreatment functions.

According to a further embodiment, said outer cone accommodates a flow-through diesel oxidation catalyst and a flow-through ammonia clean up catalyst and said inner cone accommodates a wall-flow selective catalytic reduction system comprising a diesel particulate filter.

An advantage of this embodiment is that it allows to group wall-flow and flow-through channels in a more complex way, to optimize the behavior for particular aftertreatment functions.

According to another embodiment, the disclosure provides an internal combustion engine equipped with an aftertreatment system according to any of the previous embodiments:

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an after-treatment system according to state of the art Figure 2 is a) a scheme of a flow-through catalyst and b) a wall-flow filter Figure 3 is a scheme of an aftertreatment system according to an embodiment of the present inventiort Figure 4 is a schematic view of another embodiment of the present invention.

Figure 5 is a schematic view of a further embodiment of the present invention.

Figure 6 is a schematic view of a still further embodiment of the present invention.

Figure 7 is a schematic view of still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an internal combustion engine (ICE) 110, as schematized in Fig. 1, comprising an exhaust system 270. The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment systems 280.

The aftertreatment systems may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment systems 280 include1 but are not limited to, catalytic converters (two and three way), oxidation catalysts (DCC) 261, lean NOx traps (LNT) 282, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems 283, particulate filters (DPF) 284 or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF).

Considering the fluid-dynamic the known aftertreatment systems can be divided into two main groups. At the first group belong the flow-through devices 285 (see Fig. 2a), so called since the chemical reactions (CO oxidation, NOx reduction, etc.) take place when the exhaust gas flow-through channels of the catalyst substrate. This is the case, for example, of DOC, LNT, and SCR devices. At the second group (see Fig. 2b) belong the wall-flow filters 286 (typically the DPF), since their action, the trap of soot, happens when the exhaust gases pass through the porous wall of the filter surface.

Fig. 3 shows how to reduce the number of substrates in an aftertreatment system, ideally up to only one, being the single substrate able to perform all functions required by a whatever complex aftertreatment system. A ceramic substrate 500 can be configured as both a wall-flow filter and a flow-through catalyst, by selectively plugging the exhaust gas channels 511, 521, 522 within the substrate. This is done by selectively installing and arranging the channel ends 523, 524 end with plugs 530 so that a part of the exhaust channels 521, 522, wall-flow portion 520, divert the exhaust gas through the substrate wall (having porous surfaces 525) as in a filter device, like the DPF. Within the same substrate 500, in another portion, flow-through portion 510, a second part of the exhaust channels 511 is left open on both ends 512, 513, thus maintaining a flow1hrough path in parallel to the wall-flow channels. In other words the substrate 500 comprises a plurality of exhaust gas channels 511, 521, 522, wherein some exhaust channels 511 are open at both ends 512, 513, thus creating at least a flow-through portion 510, 610, 710, 810, 910 of the substrate, and other channels 521, 522 have a porous surface 525 and are plugged at one end 523, 524, thus creating at least a wall-flow portion 520, 620, 720, 820, 920 of the substrate.

The system would be configured as follows. Exhaust gases would enter the flow-through channels 511 of the flow-through portion 510 at one end of the substrate 500. Upon exiting the opposite end on the substrate, the gas would be redirected into the inlet channels of the wall-flow portion 520 of the substrate. Within this portion of the device, the exhaust gases would pass through the substrate wall and into the outlet channels, leading to the end of the substrate. Mixing of the filtered and unfiltered gas stream would be preventing by walls separating the flow-through channels from the wall-flow channels at the inlet end of the substrate. By combining (in whatever possible combination) flow-through portions and wall-flow portions, all kind of aftertreatment systems and related functions can be obtained into the single substrate. This is realized by a substrate 500, 600, 700, 800, 900 comprising an outer cone 650, 750, 850, 910, configured to accommodate exhaust channels 511 open at both ends 512, 513, an inner cone 670! 770, 870, 920, configured to accommodate exhaust channels 521, 522 having a porous surfaces 525 and plugged at one end 523, 524, and a portion 660, 760, 860 through which the exhaust gases are redirected from the outer cone to the inner cone.

Therefore the single substrate can provide all the different functions which are required by an aftertreatment system (e.g. catalytic oxidations, filtering, cleaning): in fact, its outer cone accommodates exhaust channels open at both ends, that is to say, channels where exhaust gases can flow-through and the catalytic reactions (oxidations, reductions) can take place, while its inner cone accommodate exhaust channels having a porous surface and plugged at one end, that is to say, channels where filtering processes can take place. Moreover, a suitable layout to redirect exhaust gases from the outer cone (flow through part of the substrate) to the inner cone (wall-flow part of the substrate) is also provided inside the single substrate.

Some possible and exemplifying embodiments of the invention are now described. In fig. 4 a first embodiment is shown and is a DOC!DPF system, which is, at least for engine applications according to the Euro 4 emission standard (and inferiors) the most used aftertreatment system. The substrate 600 comprises an outer cone 650, accommodating a flow-through diesel oxidation catalyst and an inner cone 670, accommodating a wall-flow diesel particulate filter. The outer cone 650 comprises an inlet pipe 640, through which the exhaust gases enter the substrate 600, while the inner cone 670 comprises an outlet pipe 680, through which the exhaust gases exit the substrate 600. The substrate also comprises a portion 660, in between the flow-through portion 610 and the wall-flow portion 620, through which the exhaust gases are redirected from the outer cone to the inner cone. Therefore, according to this embodiment, the exhaust gases enter 640 the substrate 600 through an outer cone 650. They are directed to the DOG annular ring, i.e. the flow-through portion 610 of the substrate 600. Then, the gases are redirected 660 from the DOC outlet to the inlet of the wall-flow portion 620 of the substrate, the inner cone 670, which is arranged as a DPF. Finally, the gas exits 680 the catalyst substrate 600 through the inner cone 670.

Alternative arrangements can be devise to facilitate a more conventional arrangement: Fig. 5 shows a second embodiment of the invention, which is another DOC/DPF example and is very similar to the previous one. In fact, also in this example, the exhaust gases enter the substrate 700, by means of an inlet pipe 740 and flow-through an outer cone 750. They are directed to the DCC annular ring, i.e. the flow-through portion 710 of the substrate 700. Then1 in a portion 760 of the substrate 700, the gases are redirected from the DOC outlet to the inlet of the wall-flow portion 720 of the substrate, the inner cone 770, which is arranged as a DPF. Finally the gas exits the substrate 700 through an outlet pipe 780. The difference with respect to the previous embodiment is the fact that both inlet pipe 740 and outlet pipe 780 of the substrate 700 are coaxial with the longitudinal axis of the substrate. In this way, a more conventional "In One End and Out the Other" arrangement can be obtained.

Other components can be added to implement more complex aftertreatment functions, like the one shown in Fig. 6. In this example, the substrate 800 comprises an outer cone 850, accommodating a flow-through diesel oxidation catalyst and an inner cone 870 accommodating a wall-flow selective catalytic reduction system comprising a diesel particulate filter. The outer cone 850 comprises an inlet pipe 840 and the inner cone 870 comprises an outlet pipe 880, being both inlet pipe 840 and outlet pipe 880 coaxial with the longitudinal axis of the substrate 800. The substrate 800 also comprises a further portion 860, through which the exhaust gases are redirected from the outer cone to the inner cone, said portion 860 being provided with an urea injector 890 and a mixing device 895. Therefore, according to this embodiment, the exhaust gases enter the substrate 800 through the inner pipe 840 and flow-through the outer cone 850, i.e. the flow-through portion 810 of the substrate 800, which is arranged as a DOC. Then, in the substrate portion 860, the gases are redirected from the DOC outlet to the inlet of the wall-flow portion 820 of the substrate, the inner cone 670, which is arranged as a DPF/SCR. Before the gases entering the wall-flow section, an urea injector 890 provides the needed urea for the reaction in the SCR and gases and urea are mixed by a known mixing device 895. Finally, the exhaust gases exit the substrate 800 through the outlet pipe cone 880.

A further example is shown in Fig. 7: the substrate 900 has an outer cone 910, accommodating a flow-through diesel oxidation catalyst 930 and a flow-through ammonia clean up catalyst 940 and an inner cone 920 accommodating a wall-flow selective catalytic reduction system comprising a diesel particulate filter.

Various shape substrates could be considered: round, oval, rectangular. Wall-flow and flow-through channels could be grouped in various ways to optimize the behavior for a particular aftertreatment function. The substrate could provide for multiple passes rather than simply two. For example, one section of the substrate could serve as a DOG, a second section could be a flow-through SCR, the third section could be a wall-flow DPF, while a fourth section could be a flow-through ammonia clean up catalyst.

Gatalyst washcoats on the various portions of the device can be optimized for regional emission requirements. For instance1 EU5 could be mt with a DOC and DPF washcoat.

EU6 might use an LNT and DPF washcoat. North American emissions could use DOG and SCR on wall-flow combined with urea injection. Variations on these themes are possible in order to arrive at cost and performance optimized solutions.

Summarizing, the disclosed aftertreatment system shows remarkable advantages: reduces the number of substrates, as well as the number of devices, canning and matting. This implies mass and cost reduction. The resulting configurations would share heat between portions rather than passing the heat to the metal canning, thus facilitating retention of vital heat within the aftertreatment components. Finally, it provides additional opportunity for improved packaging configurations which, in turn, can facilitate more effective aftertreatment options.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

internal combustion engine 270 exhaust system 275 exhaust pipe 280 aftertreatment systems 281 diesel oxidation catalyst (DOC) 282 lean NOx trap (LNT) 283 selective catalytic reduction (SCR) system 284 particulate filters (DPF) 285 flow-through device 286 wall-flow filter 500 substrate 510 flow4hrough portion of the substrate 511 flow-throughchannel (open ends) 512 inlet end of flow-through channel 513 outlet end of flow-through channel 514 coating of flow-through channel 520 wall-flow portion of the substrate 521 wall-flow channel (plugged inlet end) 522 wall-flow channel (plugged outlet end) 523 plugged inlet end of wall-flow channel 524 plugged outlet end of wall-flow channel 525 porous surface of wall-flow channel 530 channel plug 600 substrate 610 flow-through portion of the substrate 620 waIl-flow portion of the substrate 640 outer cone inlet 650 outer cone 660 gas redirection path 670 innercone 680 inner cone outlet 700 substrate 710 flow-through portion of the substrate 720 wall-flow portion of the substrate 740 outer cone inlet 750 autercone 760 gas redirection path 770 inner cone 780 inner cone outlet 800 substrate 810 flow-through portion of the substrate 820 wall-flow portion of the substrate 840 outer cone inlet 850 outer cone 860 gas, redirection path 870 inner cone 880 inner cone outlet 890 urea injector 895 mixing device 900 substrate 910 outer cone of the substrate 920 inner cone of the substrate 930 flow-through portion of the outer cone 940 NH3 clean up portion of the outer cone

Claims

CLAIMS1. Aftertreatrnent system (280) for purifying exhaust gases of an automotive vehicle having an internal combustion engine, the aftertreatment system comprising a single substrate (500, 600, 700, 800, 900) with a plurality of exhaust gas channels (511, 521, 522), wherein some exhaust channels (511) are open at both ends (512, 513) and other channels (521, 522) have a porous surface (525) and are plugged at one end (523, 524), characterized in that the substrate (500, 600, 700, 800, 900) comprises an outer cone (650, 750, 850, 910), configured to accommodate exhaust channels (511) open at both ends (512, 513), an inner cone (670, 770, 870, 920), configured to accommodate exhaust channels (521, 522) having a porous surfaces (525) and plugged at one end (523, 524), and a portion (660, 760, 860) through which the exhaust gases are redirected from the cuter cone to the inner cone.
2. Aftertreatment system (280) according to claim 1, wherein said outer cone (650, 750) accommodates a flow-through diesel oxidation catalyst and said inner cone (670, 770) accommodates a wall-flow diesel particulate filter.
3. Aftertreatment system (280) according to claim 2 wherein said outer cone (650, 750) comprises an inlet pipe (640, 740), through which the exhaust gases enter the substrate (600, 700) and said inner cone (670, 770) comprises an outlet pipe (680, 780), through which the exhaust gases exit the substrate (600, 700).
4. Aftertreatment system (280) according to claim 3 wherein both inlet pipe (740) and outlet pipe (780) of the substrate (700) are coaxial with the substrate itself.
5. Aftertreatment system (280) according to claim 1, wherein said outer cone (850) accommodates a flow-through diesel oxidation catalyst and said inner cone (870) accommodates a wall-flow selective catalytic reduction system comprising a diesel particulate filter
6. Aftertreatment system (280) according to claim 5, wherein said outer cone (850) comprises an inlet pipe (840), through which the exhaust gases enter the substrate (800), said inner cone (870) comprises an outlet pipe (880), through which the exhaust gases exit the substrate (800), being bath inlet pipe (840) and outlet pipe (880) coaxial with the substrate (800), and said portion (860), through which the exhaust gases are redirected from the outer cone to the inner cone, is provided with an urea injector (890) and a mixing device (895).
7. Aftertreatment system (280) according to claim 1, wherein said outer cone (910) accommodates a flow-through diesel oxidation catalyst (930) and a flow-through ammonia clean up catalyst (940) and said inner cone (920) accommodates a wall-flow selective catalytic reduction system comprising a diesel particulate filter.
8. Internal combustion engine (110) equipped with an aftertreatrnent system (280) according to any of the preceding claims.