WO2011110885A1 - Mixing system for an exhaust gas after-treatment arrangement - Google Patents

Mixing system for an exhaust gas after-treatment arrangement Download PDF

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Publication number
WO2011110885A1
WO2011110885A1 PCT/IB2010/000757 IB2010000757W WO2011110885A1 WO 2011110885 A1 WO2011110885 A1 WO 2011110885A1 IB 2010000757 W IB2010000757 W IB 2010000757W WO 2011110885 A1 WO2011110885 A1 WO 2011110885A1
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WO
WIPO (PCT)
Prior art keywords
mixing chamber
mixing
mixing system
distribution device
exhaust gases
Prior art date
Application number
PCT/IB2010/000757
Other languages
French (fr)
Inventor
Daniel Staskowiak
Solinne Moretti
Karine Chandes
Original Assignee
Renault Trucks
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Renault Trucks filed Critical Renault Trucks
Priority to PCT/IB2010/000757 priority Critical patent/WO2011110885A1/en
Publication of WO2011110885A1 publication Critical patent/WO2011110885A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/08—Other arrangements or adaptations of exhaust conduits
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F23/00—Mixing according to the phases to be mixed, e.g. dispersing or emulsifying
    • B01F23/20—Mixing gases with liquids
    • B01F23/21—Mixing gases with liquids by introducing liquids into gaseous media
    • B01F23/213—Mixing gases with liquids by introducing liquids into gaseous media by spraying or atomising of the liquids
    • B01F23/2132—Mixing gases with liquids by introducing liquids into gaseous media by spraying or atomising of the liquids using nozzles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/10—Mixing by creating a vortex flow, e.g. by tangential introduction of flow components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F25/30—Injector mixers
    • B01F25/31—Injector mixers in conduits or tubes through which the main component flows
    • B01F25/313—Injector mixers in conduits or tubes through which the main component flows wherein additional components are introduced in the centre of the conduit
    • B01F25/3131—Injector mixers in conduits or tubes through which the main component flows wherein additional components are introduced in the centre of the conduit with additional mixing means other than injector mixers, e.g. screens, baffles or rotating elements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2892—Exhaust flow directors or the like, e.g. upstream of catalytic device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/04—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using kinetic energy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
    • B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
    • B01F2025/93—Arrangements, nature or configuration of flow guiding elements
    • B01F2025/931—Flow guiding elements surrounding feed openings, e.g. jet nozzles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/20—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a flow director or deflector
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2470/00—Structure or shape of gas passages, pipes or tubes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/08—Adding substances to exhaust gases with prior mixing of the substances with a gas, e.g. air
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to a mixing system for an exhaust gases after-treatment arrangement, comprising a mixing chamber.
  • Said system is especially designed to improve the mixing of a fluid with the exhaust gases of a thermal engine, while also preventing the solid deposits of said fluid on the mixing chamber wall.
  • the present invention can be used for example in an exhaust pipe of a diesel engine wherein an aqueous solution of urea is injected in view of an after-treatment of the exhaust gases.
  • Exhaust gases formed in the combustion of fuel in an internal combustion engine may contain a proportion of undesirable substances such as nitrogen oxides (NOx), carbon monoxide (CO), un-burnt hydrocarbons (HC), soot, etc...
  • NOx nitrogen oxides
  • CO carbon monoxide
  • HC un-burnt hydrocarbons
  • soot soot
  • a common exhaust gases after-treatment system is a so called selective catalytic reduction (SCR) system.
  • SCR selective catalytic reduction
  • Exhaust gases wherein ammonia is added as a reducer is treated in a specific catalytic converter where nitrogen oxides are converted into water and nitrogen which are both non toxic substances.
  • Ammonia is introduced in the form of urea in an aqueous solution from which ammonia is obtained through hydrolysis.
  • Urea is usually nebulised in the exhaust gas upstream of the catalytic converter.
  • a urea injection nozzle is fitted on the exhaust line upstream from the catalytic converter.
  • One conventional device generally referred to as a "swirl box"
  • a mixing chamber which is inserted in the exhaust pipe, in which the exhaust gases can flow and in which urea is injected.
  • urea can crystallize.
  • the aqueous solution of urea which is sprayed through the nozzle inside the mixing chamber tends to form a solid deposit on the mixing chamber wall.
  • a solid deposit can be formed opposite of the injection point.
  • such a deposit is likely to be formed on other parts of the mixing chamber wall since the aqueous solution of urea can wet said mixing chamber wall not only opposite of the injection point. The consequence is that the cross section of the exhaust pipe is progressively reduced, which makes the engine efficiency decrease and which can seriously impair the engine operation in the long term.
  • the invention concerns a mixing system for an exhaust gases after-treatment arrangement, said mixing system comprising:
  • a mixing chamber having a longitudinal axis and a peripheral wall, in which exhaust gases can flow towards an outlet of said mixing chamber;
  • nozzle designed to inject a fluid inside the mixing chamber from an injection inlet arranged in a wall of the mixing system, along a main injection direction;
  • the mixing system further comprises a distribution device coupled to the mixing chamber upstream from said mixing chamber, said distribution device having an inlet from which a flow of exhaust gases can enter the distribution device and comprising deflecting means arranged to divide the flow of exhaust gases into N subflows, each subflow entering the mixing chamber substantially tangentially through a corresponding peripheral inlet, the N peripheral inlets being substantially regularly angularly spaced around the longitudinal axis of said mixing chamber.
  • the invention provides multiple passageways towards the mixing chamber, through multiple tangential inlets angularly spaced around the longitudinal axis.
  • the N subflows which enter the mixing chamber all around from the injection inlet, surround the spray of the injected fluid, generate turbulence, and preferably create a peripheral swirl inside the mixing chamber around said spray.
  • the N subflows prevent the fluid from wetting the mixing chamber wall, or at least greatly reduces this wetting effect.
  • solid deposits are avoided or highly limited.
  • the N subflows help promoting the mixing between the fluid (or the gases obtained by the decomposition of said fluid) and the exhaust gases and, in case the fluid is an aqueous solution of urea, improves the decomposition of liquid urea into gases.
  • the mixing system according to the invention is much more effective than prior art systems in terms of evaporation, decomposition and mixing, and makes it possible to greatly reduce the solid deposits on the mixing chamber inside surface.
  • the invention provides a mixing system of reduced size.
  • the distribution device comprises:
  • annulus member arranged upstream and around the mixing chamber, said annulus member having an open inner face allowing the fluid communication with the mixing chamber;
  • an inlet manifold capable of collecting exhaust gases from the distribution device inlet and carrying them towards the annulus member
  • the inlet manifold can comprise a duct which is wound around the annulus member along a winding portion covering at least part of the periphery of said annulus member, substantially the whole surface area of said winding portion being open in order to allow the fluid communication between said duct and said annulus member.
  • the exhaust gases collected by the inlet manifold are given a rotating effect before they enter the annulus member, where they are further rotated.
  • the exhaust gases thus enter the mixing chamber with a quite high kinetic energy, which improves the screening effect between the fluid spray and the mixing chamber wall, and which also promotes the mixing between the exhaust gases and the injected fluid.
  • the winding portion covers between 40% and 60% of the periphery of said annulus member.
  • At least one deflecting means comprises an outer portion capable of diverting part of the exhaust gases flowing in the distribution device towards the mixing chamber, and an inner portion capable of generating a swirl inside said mixing chamber.
  • a deflecting means can therefore be shaped as a curved plate forming a vane and can have both functions.
  • the outer portion of the deflecting means can be located in the inlet manifold and/or in the annulus member, and the inner portion of the deflecting means can be located between the mixing chamber longitudinal axis and the open inner face of the annulus member.
  • the distribution device can be rotated around the mixing chamber, around the longitudinal axis of said mixing chamber.
  • deflecting means having the shape of vanes fastened to the mixing chamber, this arrangement where the distribution device can be rotated like a cap makes it possible to vary the peripheral inlets surface area and to give the expected efficiency to the swirl.
  • the injection inlet can be arranged in the distribution device, slightly upstream from the N peripheral inlets, although downstream locations can also be envisaged.
  • the angle between the injection direction and the mixing chamber longitudinal axis can be between 0° and 30°, for example around 0° (i.e. the fluid is injected substantially axially).
  • the inlet of the distribution device and the outlet of the mixing chamber may be substantially parallel, and may even have substantially the same axis.
  • a specific application of the invention is the treatment of NOx in exhaust gases.
  • said mixing system is inserted in an exhaust pipe of a diesel engine and the fluid can comprise a reducing agent for nitrogen oxides (NOx), such as ammonia, or a precursor of ammonia such as an aqueous solution of urea.
  • NOx nitrogen oxides
  • the injection inlet may be arranged in a wall substantially opposite the mixing chamber outlet.
  • the subflows are of substantially equal flow rate.
  • the invention makes it possible to obtain a satisfactory mixing between exhaust gases and urea and then, further downstream, between NOx and ammonia when urea has broken down. Therefore, it is possible to effectively reduce the NOx compounds and to achieve considerably lower NOx emissions. At the same time, the invention effectively prevents urea that has not broken down into ammonia yet from making a deposit on the mixing chamber wall, in particular opposite its injection inlet, thereby increasing the service life of said mixing chamber.
  • Figure 1 is a perspective view of a mixing system according to the invention, comprising a mixing chamber, a nozzle, and a distribution device;
  • Figure 2 is a section of the mixing system of Figure 1 , in a plane comprising the longitudinal axis of the mixing chamber and the injection direction of the nozzle;
  • Figure 3 is a perspective view of the mixing chamber and three deflection means
  • Figure 4 is a perspective view of the distribution device and the three deflection means
  • Figure 5 is a cross section of the distribution device showing three peripheral inlets towards the mixing chamber;
  • Figure 6 is a partially cut perspective front view of the mixing system
  • Figure 7 is a partially cut perspective rear view of the mixing system
  • FIGS 8 to 11 are partially cut perspective views showing the flow and subflows of the exhaust gases.
  • Figure 1 shows a mixing system 1 which, in use, is inserted in an exhaust pipe of an engine arrangement, typically a diesel engine arrangement.
  • the mixing system 1 comprises a mixing chamber 2 having a longitudinal axis 3, a substantially cylindrical peripheral wall 4, and open ends one of which forms the outlet 5 of said mixing chamber 2.
  • the engine exhaust gases carried by the exhaust pipe enter the mixing system 1 according to a flow direction FD, then enter the mixing chamber 2 (as will be explained in the following description) and flow inside it towards the outlet 5, where said gases are directed towards a non depicted catalytic converter before being released into the atmosphere.
  • the mixing chamber 2 Inside the mixing chamber 2 is achieved the mixing between the exhaust gases and an injected flow of fluid.
  • the fluid can comprise and/or a precursor of ammonia such as an aqueous solution of urea.
  • the general flow direction FD of exhaust gases is substantially parallel to the mixing chamber longitudinal axis 3.
  • the words “upstream” and “downstream” are used with respect to said flow direction FD.
  • the word “inner” refers to a part located closer to the axis 3 as opposed to the word “outer”.
  • the mixing system 1 further comprises a distribution device 6 coupled to the mixing chamber 2 upstream of the chamber.
  • the distribution device is at least partially arranged around the mixing chamber.
  • Said distribution device 6 is designed to collect the exhaust gases flowing in the exhaust pipe and to carry them towards the mixing chamber with an appropriate distribution and kinetic effect, in order to promote the mixing between said gases and the injected urea.
  • the distribution device 6 comprises an annulus member 7 arranged upstream and around the mixing chamber 2.
  • the annulus member 7 includes:
  • downstream end wall 9 shaped as a ring, which extends substantially radially and connects the upstream edge of the mixing chamber peripheral wall 4 and the downstream edge of the annulus member peripheral wall 8;
  • an upstream end wall 10 having a central portion 11 which forms substantially a disc orthogonal to the axis 3, and a conical portion 12 which connects said central portion 11 and the upstream edge of the annulus member peripheral wall 8 and which is tapered towards the downstream direction.
  • the annulus member 7 has an open inner face, located in the continuation of the mixing chamber peripheral wall 4, which allows the exhaust gases to flow from the annulus member 7 towards the mixing chamber 2.
  • the central portion 11 of the upstream end wall 10 of the annulus member 7 is provided with an injection inlet 13 preferably arranged on the longitudinal axis 3.
  • a nozzle 14 fitted in said injection inlet 13 is designed to inject an aqueous solution of urea inside the mixing chamber 2, along a main injection direction ID, thereby forming a spray 15.
  • the angle between the main injection direction ID and the longitudinal axis 3, i.e. the flow direction FD, can be in the range of 0° - 30°.
  • the aqueous solution of urea is injected substantially axially inside the mixing chamber 2.
  • the distribution device 6 further comprises an inlet manifold 16 having an upstream portion 17 which is connected to the exhaust gases pipe, on the engine side, and which defines the inlet 18 of the mixing system 1.
  • said upstream portion 17 is substantially straight.
  • the inlet manifold 16 also comprises a downstream portion forming a duct 19 which is wound around the annulus member 7 along a winding portion covering part of the periphery of said annulus member 7, typically between 40% and 60% of the periphery of said annulus member 7.
  • the cross section of the duct 19 decreases from around the cross section of the upstream portion 17 of the inlet manifold 16 to zero, the outer surface of the inlet manifold 16 merging progressively with the peripheral wall 8 of the annulus member 7.
  • the winding portion forms a curved and oblong shape on the peripheral wall 8 of the annulus member 7. Said winding portion is open, in order to allow the exhaust gases to flow from the inlet manifold 16 towards the annulus member 7.
  • the mixing system 1 further comprises deflecting means, here consisting of three substantially identical vanes 20.
  • the vanes 20 are fastened to the mixing chamber 2, upstream from it, as shown on Figure 3, and substantially regularly angularly spaced around the longitudinal axis 3 of said mixing chamber 2.
  • the vanes 20 are located inside the distribution device, as shown on Figures 2 and 4.
  • Each vane 20 is made of a curved plate which extends, from its upstream edge 21 towards its downstream edge 22, from the peripheral wall 8 of the annulus member 7 towards the axis 3 while roughly following an arc of a circle which extends around said axis 3 and comes closer to said axis 3 (see Figure 5).
  • the vane 20 comprises an outer portion 23 (upstream) located in the inlet manifold 16 and/or in the annulus member 7 and capable of diverting part of the exhaust gases flowing in the distribution device 6 towards the mixing chamber 2.
  • the vane 20 also comprises an inner portion 24 (downstream) located between the mixing chamber longitudinal axis 3 and the open inner face of the annulus member 7, said inner portion 24 being capable of generating a swirl inside said mixing chamber 2.
  • the end part of the inner portion 24 forms a backward bend 25.
  • a first vane 20a has its upstream edge 21 located substantially in the vicinity of the upstream end of the duct 19. Then, a second vane 20b has its upstream edge 21 located 120° further downstream, in the downstream portion of the duct 19. Finally, a third vane 20c has its upstream edge 21 located 120° further downstream, downstream from the downstream end of the duct 19.
  • the vanes 20 form three successive passageways for the exhaust gases from the inlet manifold 16 to the annulus member 7 and then towards the mixing chamber 2.
  • Three successive peripheral inlets 26 are thus formed in the open inner face of the annulus member 7, through which the exhaust gases can flow from the annulus member 7 towards the mixing chamber 2.
  • the three peripheral inlets 26 are substantially regularly angularly spaced around the longitudinal axis 3 of the mixing chamber 2.
  • the three peripheral inlets 26 substantially have the same cross section, and they are arranged downstream or essentially at the same level as the injection inlet. Nevertheless, the peripheral inlets 26 could also be located upstream of the injection inlet 13.
  • the vanes 20 and the distribution device 6 are shaped, located and sized up so that the whole flow of exhaust gases entering the distribution device 6 by the inlet 18 is divided into three sub-flows, which are preferably of substantially equal flow rate.
  • Each subflow enters the mixing chamber 2 substantially tangentially through a corresponding peripheral inlet 26 and is then further rotated by means of the inner portion 24 of the vane 20.
  • substantially tangentially it is meant that the sub-flows are not injected along a radial direction, but preferably with a direction which is at least at 45 degrees, and preferably at least 60 degrees from such radial direction when viewed in a plane perpendicular to the axis 3 of the mixing chamber.
  • each subflow is also preferably oriented slightly downwardly, for example with an angle in the range of 10 to 45 degrees, with respect to a plane perpendicular to axis 3, when viewed in a tangential plane.
  • each subflow tends to initiate in the mixing chamber a helical flow path along the peripheral wall of the mixing chamber.
  • the whole flow F of exhaust gases enters the distribution device 6 through the inlet 18 ( Figure 8).
  • the whole flow is divided by the first vane 20a into:
  • the third vane 20 c is designed to direct the whole third subflow F3 towards the third peripheral inlet 26c to make it enter the mixing chamber 2 (see Figure 11).
  • One significant advantage of the invention is that there are formed three subflows F1 , F2, F3 of exhaust gases entering the mixing chamber substantially tangentially, thereby forming a peripheral swirl which surrounds the urea spray 15.
  • the velocity of gases along the peripheral wall 4 of the mixing chamber 2 is quite high, and the injected aqueous solution of urea is prevented from wetting the inner face of the mixing chamber peripheral wall 4.
  • the three subflows draw the injected fluid further downstream while also improving the mixing of said fluid with the exhaust gases and the complete chemical decomposition of urea.
  • the distribution device 6 can be rotated around the mixing chamber 2, around the longitudinal axis 3.
  • the distribution device 6 can be easily put up in an existing mixing system or can be part of a new mixing system.
  • the invention is not restricted to the embodiment described above by way of non-limiting example, but on the contrary it encompasses all embodiments thereof.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

The mixing system (1) comprises: a mixing chamber (2) having a longitudinal axis (3), in which exhaust gases can flow towards an outlet; a nozzle designed to inject a fluid inside the mixing chamber from an injection inlet arranged in a wall of the mixing system, along a main injection direction; a distribution device (6) coupled to the mixing chamber upstream from said mixing chamber, said distribution device having an inlet from which the whole flow of exhaust gases can enter the distribution device and comprising deflecting means (20a, 20b, 20c) arranged to divide the whole flow of exhaust gases into N subflows (F1, F2, F3), each subflow entering the mixing chamber (2) substantially tangentially through a corresponding peripheral inlet (26a, 26b, 26c), the N peripheral inlets being substantially regularly angularly spaced around the longitudinal axis (3) of said mixing chamber (2).

Description

MIXING SYSTEM FOR AN EXHAUST GAS AFTER-TREATMENT
ARRANGEMENT
Field of the invention
The present invention relates to a mixing system for an exhaust gases after-treatment arrangement, comprising a mixing chamber. Said system is especially designed to improve the mixing of a fluid with the exhaust gases of a thermal engine, while also preventing the solid deposits of said fluid on the mixing chamber wall. The present invention can be used for example in an exhaust pipe of a diesel engine wherein an aqueous solution of urea is injected in view of an after-treatment of the exhaust gases.
Technological background
Exhaust gases formed in the combustion of fuel in an internal combustion engine may contain a proportion of undesirable substances such as nitrogen oxides (NOx), carbon monoxide (CO), un-burnt hydrocarbons (HC), soot, etc...
To reduce air pollution, vehicles are therefore equipped with various after-treatment systems that deal with undesirable substances in exhaust gases.
A common exhaust gases after-treatment system is a so called selective catalytic reduction (SCR) system. Exhaust gases wherein ammonia is added as a reducer is treated in a specific catalytic converter where nitrogen oxides are converted into water and nitrogen which are both non toxic substances. Ammonia is introduced in the form of urea in an aqueous solution from which ammonia is obtained through hydrolysis. Urea is usually nebulised in the exhaust gas upstream of the catalytic converter. To this end, a urea injection nozzle is fitted on the exhaust line upstream from the catalytic converter.
One conventional device, generally referred to as a "swirl box", comprises a mixing chamber which is inserted in the exhaust pipe, in which the exhaust gases can flow and in which urea is injected.
A problem with this type of exhaust gases treatment is that, before it has transformed into ammonia, urea can crystallize. In concrete terms, the aqueous solution of urea which is sprayed through the nozzle inside the mixing chamber tends to form a solid deposit on the mixing chamber wall. In particular, when the urea is sprayed according to a direction which is angled with respect to the exhaust gases flow direction, a solid deposit can be formed opposite of the injection point. Moreover, such a deposit is likely to be formed on other parts of the mixing chamber wall since the aqueous solution of urea can wet said mixing chamber wall not only opposite of the injection point. The consequence is that the cross section of the exhaust pipe is progressively reduced, which makes the engine efficiency decrease and which can seriously impair the engine operation in the long term.
Prior art swirl boxes are not fully effective since they do not make it possible to achieve the complete chemical decomposition of liquid urea into gases and/or a satisfactory mixing of urea with exhaust gases and/or cannot prevent effectively solid deposits.
It therefore appears that there is room for improvement in the systems for injecting a fluid in a pipe carrying exhaust gases and for mixing them.
Summary
It is an object of the present invention to provide an improved mixing system which can overcome the drawbacks encountered in conventional mixing systems, and particularly which prevents or at least limits the injected fluid from forming a deposit onto the mixing chamber surface while also promoting a satisfactory mixing between said injected fluid and the exhaust gases.
For this purpose, the invention concerns a mixing system for an exhaust gases after-treatment arrangement, said mixing system comprising:
- a mixing chamber having a longitudinal axis and a peripheral wall, in which exhaust gases can flow towards an outlet of said mixing chamber;
- a nozzle designed to inject a fluid inside the mixing chamber from an injection inlet arranged in a wall of the mixing system, along a main injection direction;
wherein the mixing system further comprises a distribution device coupled to the mixing chamber upstream from said mixing chamber, said distribution device having an inlet from which a flow of exhaust gases can enter the distribution device and comprising deflecting means arranged to divide the flow of exhaust gases into N subflows, each subflow entering the mixing chamber substantially tangentially through a corresponding peripheral inlet, the N peripheral inlets being substantially regularly angularly spaced around the longitudinal axis of said mixing chamber.
Therefore, thanks to the distribution device, the invention provides multiple passageways towards the mixing chamber, through multiple tangential inlets angularly spaced around the longitudinal axis. The N subflows, which enter the mixing chamber all around from the injection inlet, surround the spray of the injected fluid, generate turbulence, and preferably create a peripheral swirl inside the mixing chamber around said spray.
As a consequence, the N subflows prevent the fluid from wetting the mixing chamber wall, or at least greatly reduces this wetting effect. As a result, solid deposits are avoided or highly limited.
Moreover, the N subflows help promoting the mixing between the fluid (or the gases obtained by the decomposition of said fluid) and the exhaust gases and, in case the fluid is an aqueous solution of urea, improves the decomposition of liquid urea into gases.
With this arrangement, the mixing system according to the invention is much more effective than prior art systems in terms of evaporation, decomposition and mixing, and makes it possible to greatly reduce the solid deposits on the mixing chamber inside surface.
Furthermore, by providing N inlets integrated in a single distribution device, the invention provides a mixing system of reduced size.
According to an embodiment of the invention, the distribution device comprises:
- an annulus member arranged upstream and around the mixing chamber, said annulus member having an open inner face allowing the fluid communication with the mixing chamber;
- an inlet manifold capable of collecting exhaust gases from the distribution device inlet and carrying them towards the annulus member;
- N deflecting means being arranged inside the inlet manifold and/or in the annulus member and defining in the annulus member open inner face said N peripheral inlets. Preferably, the inlet manifold can comprise a duct which is wound around the annulus member along a winding portion covering at least part of the periphery of said annulus member, substantially the whole surface area of said winding portion being open in order to allow the fluid communication between said duct and said annulus member.
As a result, the exhaust gases collected by the inlet manifold are given a rotating effect before they enter the annulus member, where they are further rotated. The exhaust gases thus enter the mixing chamber with a quite high kinetic energy, which improves the screening effect between the fluid spray and the mixing chamber wall, and which also promotes the mixing between the exhaust gases and the injected fluid.
For example, the winding portion covers between 40% and 60% of the periphery of said annulus member.
Preferably, at least one deflecting means comprises an outer portion capable of diverting part of the exhaust gases flowing in the distribution device towards the mixing chamber, and an inner portion capable of generating a swirl inside said mixing chamber. Such a deflecting means can therefore be shaped as a curved plate forming a vane and can have both functions.
In concrete terms, the outer portion of the deflecting means can be located in the inlet manifold and/or in the annulus member, and the inner portion of the deflecting means can be located between the mixing chamber longitudinal axis and the open inner face of the annulus member.
In an implementation of the invention, the distribution device can be rotated around the mixing chamber, around the longitudinal axis of said mixing chamber. With deflecting means (having the shape of vanes) fastened to the mixing chamber, this arrangement where the distribution device can be rotated like a cap makes it possible to vary the peripheral inlets surface area and to give the expected efficiency to the swirl.
The injection inlet can be arranged in the distribution device, slightly upstream from the N peripheral inlets, although downstream locations can also be envisaged.
Preferably, N is an odd number, for example N=3.
The angle between the injection direction and the mixing chamber longitudinal axis can be between 0° and 30°, for example around 0° (i.e. the fluid is injected substantially axially). The inlet of the distribution device and the outlet of the mixing chamber may be substantially parallel, and may even have substantially the same axis.
A specific application of the invention is the treatment of NOx in exhaust gases. In that case, said mixing system is inserted in an exhaust pipe of a diesel engine and the fluid can comprise a reducing agent for nitrogen oxides (NOx), such as ammonia, or a precursor of ammonia such as an aqueous solution of urea.
The injection inlet may be arranged in a wall substantially opposite the mixing chamber outlet.
Preferably, the subflows are of substantially equal flow rate.
The invention makes it possible to obtain a satisfactory mixing between exhaust gases and urea and then, further downstream, between NOx and ammonia when urea has broken down. Therefore, it is possible to effectively reduce the NOx compounds and to achieve considerably lower NOx emissions. At the same time, the invention effectively prevents urea that has not broken down into ammonia yet from making a deposit on the mixing chamber wall, in particular opposite its injection inlet, thereby increasing the service life of said mixing chamber.
Other applications of such a mixing device can be envisioned, such as for mixing fuel with exhaust gases upstream of an oxidation catalyst in view of generating heat for cleaning a diesel particulate filter.
These and other features and advantages will become apparent upon reading the following description in view of the drawings attached hereto representing, as non-limiting examples, embodiments of a mixing system according to the invention.
Brief description of the drawings
The following detailed description of several embodiments of the invention is better understood when read in conjunction with the appended drawings being understood, however, that the invention is not limited to the specific embodiments disclosed.
Figure 1 is a perspective view of a mixing system according to the invention, comprising a mixing chamber, a nozzle, and a distribution device; Figure 2 is a section of the mixing system of Figure 1 , in a plane comprising the longitudinal axis of the mixing chamber and the injection direction of the nozzle;
Figure 3 is a perspective view of the mixing chamber and three deflection means;
Figure 4 is a perspective view of the distribution device and the three deflection means;
Figure 5 is a cross section of the distribution device showing three peripheral inlets towards the mixing chamber;
Figure 6 is a partially cut perspective front view of the mixing system;
Figure 7 is a partially cut perspective rear view of the mixing system;
Figures 8 to 11 are partially cut perspective views showing the flow and subflows of the exhaust gases.
Detailed description of an embodiment
Figure 1 shows a mixing system 1 which, in use, is inserted in an exhaust pipe of an engine arrangement, typically a diesel engine arrangement.
The mixing system 1 comprises a mixing chamber 2 having a longitudinal axis 3, a substantially cylindrical peripheral wall 4, and open ends one of which forms the outlet 5 of said mixing chamber 2.
The engine exhaust gases carried by the exhaust pipe enter the mixing system 1 according to a flow direction FD, then enter the mixing chamber 2 (as will be explained in the following description) and flow inside it towards the outlet 5, where said gases are directed towards a non depicted catalytic converter before being released into the atmosphere. Inside the mixing chamber 2 is achieved the mixing between the exhaust gases and an injected flow of fluid. In the case where the mixing device is used for reducing the NOx content of exhaust gases, the fluid can comprise and/or a precursor of ammonia such as an aqueous solution of urea.
Upstream from the mixing system 1 , the general flow direction FD of exhaust gases is substantially parallel to the mixing chamber longitudinal axis 3. The words "upstream" and "downstream" are used with respect to said flow direction FD. The word "inner" refers to a part located closer to the axis 3 as opposed to the word "outer".
The mixing system 1 further comprises a distribution device 6 coupled to the mixing chamber 2 upstream of the chamber. In the shown embodiment, the distribution device is at least partially arranged around the mixing chamber. Said distribution device 6 is designed to collect the exhaust gases flowing in the exhaust pipe and to carry them towards the mixing chamber with an appropriate distribution and kinetic effect, in order to promote the mixing between said gases and the injected urea.
The distribution device 6 comprises an annulus member 7 arranged upstream and around the mixing chamber 2. The annulus member 7 includes:
- a substantially cylindrical peripheral wall 8;
- a downstream end wall 9, shaped as a ring, which extends substantially radially and connects the upstream edge of the mixing chamber peripheral wall 4 and the downstream edge of the annulus member peripheral wall 8;
- an upstream end wall 10 having a central portion 11 which forms substantially a disc orthogonal to the axis 3, and a conical portion 12 which connects said central portion 11 and the upstream edge of the annulus member peripheral wall 8 and which is tapered towards the downstream direction.
The annulus member 7 has an open inner face, located in the continuation of the mixing chamber peripheral wall 4, which allows the exhaust gases to flow from the annulus member 7 towards the mixing chamber 2.
The central portion 11 of the upstream end wall 10 of the annulus member 7 is provided with an injection inlet 13 preferably arranged on the longitudinal axis 3. A nozzle 14 fitted in said injection inlet 13 is designed to inject an aqueous solution of urea inside the mixing chamber 2, along a main injection direction ID, thereby forming a spray 15.
The angle between the main injection direction ID and the longitudinal axis 3, i.e. the flow direction FD, can be in the range of 0° - 30°. For example, it can be envisaged that the aqueous solution of urea is injected substantially axially inside the mixing chamber 2.
The distribution device 6 further comprises an inlet manifold 16 having an upstream portion 17 which is connected to the exhaust gases pipe, on the engine side, and which defines the inlet 18 of the mixing system 1. In the illustrated embodiment, said upstream portion 17 is substantially straight.
The inlet manifold 16 also comprises a downstream portion forming a duct 19 which is wound around the annulus member 7 along a winding portion covering part of the periphery of said annulus member 7, typically between 40% and 60% of the periphery of said annulus member 7. In the downstream direction, the cross section of the duct 19 decreases from around the cross section of the upstream portion 17 of the inlet manifold 16 to zero, the outer surface of the inlet manifold 16 merging progressively with the peripheral wall 8 of the annulus member 7.
The winding portion forms a curved and oblong shape on the peripheral wall 8 of the annulus member 7. Said winding portion is open, in order to allow the exhaust gases to flow from the inlet manifold 16 towards the annulus member 7.
The mixing system 1 further comprises deflecting means, here consisting of three substantially identical vanes 20. The vanes 20 are fastened to the mixing chamber 2, upstream from it, as shown on Figure 3, and substantially regularly angularly spaced around the longitudinal axis 3 of said mixing chamber 2. Moreover, the vanes 20 are located inside the distribution device, as shown on Figures 2 and 4.
Each vane 20 is made of a curved plate which extends, from its upstream edge 21 towards its downstream edge 22, from the peripheral wall 8 of the annulus member 7 towards the axis 3 while roughly following an arc of a circle which extends around said axis 3 and comes closer to said axis 3 (see Figure 5).
The vane 20 comprises an outer portion 23 (upstream) located in the inlet manifold 16 and/or in the annulus member 7 and capable of diverting part of the exhaust gases flowing in the distribution device 6 towards the mixing chamber 2. The vane 20 also comprises an inner portion 24 (downstream) located between the mixing chamber longitudinal axis 3 and the open inner face of the annulus member 7, said inner portion 24 being capable of generating a swirl inside said mixing chamber 2. The end part of the inner portion 24 forms a backward bend 25.
As can be seen from Figure 4, when following the flow of exhaust gases from the inlet 18, a first vane 20a has its upstream edge 21 located substantially in the vicinity of the upstream end of the duct 19. Then, a second vane 20b has its upstream edge 21 located 120° further downstream, in the downstream portion of the duct 19. Finally, a third vane 20c has its upstream edge 21 located 120° further downstream, downstream from the downstream end of the duct 19.
The vanes 20 form three successive passageways for the exhaust gases from the inlet manifold 16 to the annulus member 7 and then towards the mixing chamber 2. Three successive peripheral inlets 26 are thus formed in the open inner face of the annulus member 7, through which the exhaust gases can flow from the annulus member 7 towards the mixing chamber 2. The three peripheral inlets 26 are substantially regularly angularly spaced around the longitudinal axis 3 of the mixing chamber 2. In the shown embodiment, the three peripheral inlets 26 substantially have the same cross section, and they are arranged downstream or essentially at the same level as the injection inlet. Nevertheless, the peripheral inlets 26 could also be located upstream of the injection inlet 13.
The vanes 20 and the distribution device 6 (especially the duct 19 and the annulus member 7) are shaped, located and sized up so that the whole flow of exhaust gases entering the distribution device 6 by the inlet 18 is divided into three sub-flows, which are preferably of substantially equal flow rate. Each subflow enters the mixing chamber 2 substantially tangentially through a corresponding peripheral inlet 26 and is then further rotated by means of the inner portion 24 of the vane 20. By substantially tangentially, it is meant that the sub-flows are not injected along a radial direction, but preferably with a direction which is at least at 45 degrees, and preferably at least 60 degrees from such radial direction when viewed in a plane perpendicular to the axis 3 of the mixing chamber.
The injection direction of each subflow is also preferably oriented slightly downwardly, for example with an angle in the range of 10 to 45 degrees, with respect to a plane perpendicular to axis 3, when viewed in a tangential plane. Thereby, each subflow tends to initiate in the mixing chamber a helical flow path along the peripheral wall of the mixing chamber.
The flow of exhaust gases is now described with reference to Figures 8 to 11.
The whole flow F of exhaust gases enters the distribution device 6 through the inlet 18 (Figure 8). When entering the duct 19 of the inlet manifold 16 (see Figures 4, 5 and 9), the whole flow is divided by the first vane 20a into:
- a first subflow F1 of exhaust gases having a flow rate of substantially one third of the global flow rate, said first subflow F1 passing along the inner face of the first vane 20a, through a first peripheral inlet 26a and then entering the mixing chamber 2;
- and a complementary flow which remains in the duct 19 and flows towards the subsequent vane 20b.
As can be seen from Figures 4, 5 and 10, said complementary flow is divided further downstream by the second vane 20b into:
- a second subflow F2 of exhaust gases having a flow rate of substantially one half of the complementary flow, i.e. substantially one third of the global flow rate, said second subflow F2 passing along the inner face of the second vane 20b, through a second peripheral inlet 26b and then entering the mixing chamber 2;
- and a third subflow F3 of exhaust gases having a flow rate of substantially one third of the global flow rate, said third subflow F3 remaining in the duct 19 and flowing towards the subsequent vane 20c.
The third vane 20 c is designed to direct the whole third subflow F3 towards the third peripheral inlet 26c to make it enter the mixing chamber 2 (see Figure 11).
One significant advantage of the invention is that there are formed three subflows F1 , F2, F3 of exhaust gases entering the mixing chamber substantially tangentially, thereby forming a peripheral swirl which surrounds the urea spray 15. As a consequence, the velocity of gases along the peripheral wall 4 of the mixing chamber 2 is quite high, and the injected aqueous solution of urea is prevented from wetting the inner face of the mixing chamber peripheral wall 4. Moreover, the three subflows draw the injected fluid further downstream while also improving the mixing of said fluid with the exhaust gases and the complete chemical decomposition of urea.
In order to vary the peripheral inlets surface area and to give the expected efficiency to the swirl, the distribution device 6 can be rotated around the mixing chamber 2, around the longitudinal axis 3.
The distribution device 6 can be easily put up in an existing mixing system or can be part of a new mixing system. Of course, the invention is not restricted to the embodiment described above by way of non-limiting example, but on the contrary it encompasses all embodiments thereof.

Claims

1. A mixing system for an exhaust gases after-treatment arrangement, said mixing system (1) comprising:
a mixing chamber (2) having a longitudinal axis (3) and a peripheral wall (4), in which exhaust gases can flow towards an outlet (5) of said mixing chamber (2);
a nozzle (14) designed to inject a fluid inside the mixing chamber (2) from an injection inlet (13) arranged in a wall (11) of the mixing system (1), along a main injection direction (ID);
characterized in that it further comprises a distribution device (6) coupled to the mixing chamber (2) upstream from said mixing chamber (2), said distribution device (6) having an inlet (18) from which a flow of exhaust gases can enter the distribution device (6) and comprising deflecting means (20, 20a, 20b, 20c) arranged to divide the flow of exhaust gases into N subflows (F1 , F2, F3), each subflow entering the mixing chamber (2) substantially tangentially through a corresponding peripheral inlet (26, 26a, 26b, 26c), the N peripheral inlets being substantially regularly angularly spaced around the longitudinal axis (3) of said mixing chamber (2).
2. The mixing system according to claim 1 , characterized in that the distribution device (6) comprises:
an annulus member (7) arranged upstream and around the mixing chamber (2), said annulus member (7) having an open inner face allowing the fluid communication with the mixing chamber (2);
an inlet manifold (16) capable of collecting exhaust gases from the distribution device inlet (18) and carrying them towards the annulus member (7);
- N deflecting means (20, 20a, 20b, 20c) being arranged inside the inlet manifold (16) and/or in the annulus member (7) and defining in the annulus member open inner face said N peripheral inlets (26, 26a, 26b, 26c).
3. The mixing system according to claim 2, characterized in that the inlet manifold (16) comprises a duct (19) which is wound around the annulus member (7) along a winding portion covering at least part of the periphery of said annulus member (7), substantially the whole surface area of said winding portion being open in order to allow the fluid communication between said duct (19) and said annulus member (7).
4. The mixing system according to claim 3, characterized in that the winding portion covers between 40% and 60% of the periphery of said annulus member (7).
5. The mixing system according to any one of claims 1 to 4, characterized in that at least one deflecting means (20) comprises an outer portion (23) capable of diverting part of the exhaust gases flowing in the distribution device (6) towards the mixing chamber (2), and an inner portion (24) capable of generating a swirl inside said mixing chamber (2).
6. The mixing system according to claim 5 in combination with claim 2, characterized in that the outer portion (23) of the deflecting means (20) is located in the inlet manifold (16) and/or in the annulus member (7), and in that the inner portion (24) of the deflecting means (20) is located between the mixing chamber longitudinal axis (3) and the open inner face of the annulus member (7).
7. The mixing system according to any one of claims 1 to 6, characterized in that the distribution device (6) can be rotated around the mixing chamber (2), around the longitudinal axis (3) of said mixing chamber (2).
8. The mixing system according to any one of claims 1 to 7, characterized in that the injection inlet (13) is arranged in the distribution device (6), upstream from the N peripheral inlets (26).
9. The mixing system according to any one of claims 1 to 8, characterized in that N > 3.
10. The mixing system according to any one of claims 1 to 9, characterized in that N is an odd number, for example N=3.
11. The mixing system according to any one of claims 1 to 10, characterized in that the angle between the main injection direction (ID) and the mixing chamber longitudinal axis (3) is between 0° and 30°, for example around 0°.
12. The mixing system according to any one of claims 1 to 11 , characterized in that the inlet (18) of the distribution device (6) and the outlet (5) of the mixing chamber (2) are substantially parallel.
13. The mixing system according to any one of claims 1 to 12, characterized in that it is inserted in an exhaust pipe arrangement of a diesel engine arrangement and in that the fluid comprises a reducing agent for nitrogen oxides (NOx).
14. The mixing system according to any one of claims 1 to 13, characterized in that the injection inlet (13) is arranged in a wall (11) substantially opposite the mixing chamber outlet (5).
15. The mixing system according to any one of claims 1 to 14, characterized in that the subflows (F1 , F2, F3) are of substantially equal flow rate.
PCT/IB2010/000757 2010-03-11 2010-03-11 Mixing system for an exhaust gas after-treatment arrangement WO2011110885A1 (en)

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